Abstracts of the Annual Meeting of 

Planetary Geologic Mappers, 

Nampa, Idaho 2006 

Edited By Tracy K.P. Gregg,1 Kenneth L. Tanaka,2 and R. Stephen Saunders3

Open-File Report 2006-1263 

2006 

Any use of trade, firm, or product names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

1

 The State University of New York at Buffalo, Department of Geology, 710 Natural 

Sciences Complex, Buffalo, NY 14260-3050. 

2

 U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001. 

3

 NASA Headquarters, Office of Space Science, 300 E. Street SW, Washington, DC 20546. 
Report of the Annual Mappers Meeting 

Northwest Nazarene University 

Nampa, Idaho 

June 30 – July 2, 2006 

Approximately 18 people attended this year’s mappers meeting, and many more 

submitted abstracts and maps in absentia. The meeting was held on the campus of 

Northwest Nazarene University (NNU), and was graciously hosted by NNU’s School of 

Health and Science. Planetary mapper Dr. Jim Zimbelman is an alumnus of NNU, and he 

was pivotal in organizing the meeting at this location. Oral and poster presentations were 

given on Friday, June 30. Drs. Bill Bonnichsen and Marty Godchaux led field excursions 

on July 1 and 2. 

USGS Astrogeology Team Chief Scientist Lisa Gaddis led the meeting with a brief 

discussion of the status of the planetary mapping program at USGS, and a more detailed 

description of the Lunar Mapping Program. She indicated that there is now a functioning 

website (http://astrogeology.usgs.gov/Projects/PlanetaryMapping/Lunar/) which shows 

which lunar quadrangles are available to be mapped. Like other USGS-published maps, 

proposals to complete a lunar geologic map must be submitted to the regular Planetary 

Geology & Geophysics (PGG) program for peer review. Jim Skinner (USGS) later 

presented the progress of the 1:2.5M-scale map of the lunar Copernicus quadrangle, and 

demonstrated the wide range of data that are available to support these maps. Gaddis and 

Skinner encouraged the community to submit proposals for generating lunar geologic 

maps, and reminded us that, as for all planetary maps, the project must be science-driven. 

Venus mapper Jim Zimbelman of the Smithsonian Institution (SI) presented the progress 

for his V-15 and V-16 quadrangles; Vicki Hansen (University of Minnesota Duluth) 

showed her preliminary work on V-45. Zimbelman addressed an issue that has been 

plaguing the community: “delinquent Venus mappers.” In short, there were a number of 

Venus maps funded in the early 1990s under the Venus Data Analysis Program (VDAP). 

Unfortunately, funding for this program was cut before many Venus maps could be 

completed, resulting in about 10 Venus maps that were initially assigned but have shown 

little or no progress in many years. Zimbelman announced that he was not going to be 

able to complete quadrangle V-27 that he was assigned under VDAP, and was therefore 

returning that quadrangle to the community; he invited people to propose to PGG to map 

this quadrangle. 

Dave Williams of Arizona State University (ASU) reported on the progress of his global 

Io map. His mapping team recently received the completed, controlled global mosaic 

(using Voyager and Galileo images) from the USGS; this will be the basemap for their 

geologic mapping. Furthermore, the three team members (Laszlo Keszthelyi, David 

Crown and Dave Williams) have calibrated their individual mapping techniques by each 

mapping the same region for comparison. Thomas Doggett (ASU) showed progress on 

the global Europa map that was awarded to Ron Greeley. There was some consternation 

expressed on the methodology for determining relative ages of the lineaments; it was 

suggested that Vicki Hansen contact Patricio Figueredo (Exxon) directly, because 

Figueredo is the one who has been developing the lineament mapping techniques. 
Mars remains the most popular planet to map. Kevin Williams (SI) and Corey Fortezzo 

(SI) presented progress on their 1:500K maps in the Margaritifer Terra region of Mars. 

Jim Zimbelman described his 1:1M Medusae Fossae map, which is nearing completion. 

Peter Mouginis-Mark (University of Hawai’i) reported progress on his 1:200K maps of 

Tooting crater and of the Olympus Mons summit caldera. Jim Skinner discussed the 

progress of his and Ken Herkenhoff’s (USGS) map (1:500K) on the Olympia Cavi region 

of Mars’ north pole, and Eric Kolb (USGS) presented work that he and Ken Tanaka 

(USGS) are completing on the Martian south pole. David Crown of the Planetary 

Science Institute (PSI) reported on numerous 1:500K and 1:1M maps in the Hellas and 

Hesperia regions of Mars. Frank Chuang (PSI) discussed progress on mapping the 

Deuteronilus Mensae region of Mars with David Crown. Finally, Tracy Gregg 

(University at Buffalo) presented preliminary results of a 1:2M Hesperia Planum 

mapping project with David Crown. 

During discussion, it was concluded that we will attempt to hold the next mappers 

meeting in Tucson, at the Planetary Science Institute, during the 2nd or 3rd week in June. 

David Crown volunteered to coordinate that effort. At Lisa Gaddis’ suggestion, we may 

try to coordinate this with a 1-day digital mapping workshop, sponsored by the USGS. 
CONTENTS 

Venus 

Geologic Mapping of V-11 Shimti Tessera and V-12 Vellamo Planitia, Venus 

J.C. Aubele 

Geologic Mapping of the Beta Regio Quadrangle (V-17), Venus: Constraints on Beta 

Rise Evolution 

A.T. Basilevsky 

Preliminary Report on Geologic Mapping of Isabella Quadrangle (V-50) and Helen 

Planitia, Venus 

L.F. Bleamaster 

Geologic Mapping of the Guinevere Planitia Quadrangle of Venus 

D.A. Crown and E.R. Stofan 

Mapping in the Fredegonde (V-57) Quadrangle, Venus: Preliminary Results 

M.A. Ivanov and J.W. Head 

Geologic History of the Lavinia Planitia/Lada Terra Region, Venus: Results of the 

Mapping in the V-55, V-61, and V-56 Quadrangles 

M.A. Ivanov and J.W. Head 

Mapping of the V-7 Quadrangle: Sequence of Events During Formation of Lakshmi 

Planum, Venus 

M.A. Ivanov and J.W. Head 

Geology of the Juno Chasma Quadrangle (V-47), Venus 

D.A. Senske 

Geology of the Phoebe Regio Quadrangle (V-41), Venus 

D.A. Senske 

Geology of the Tellus Tessera Quadrangle (V-10), Venus 

D.A. Senske 

Mapping of Quadrangle V-53: Themis Regio 

E.R. Stofan and A.W. Brian 

Galilean Satellites 

Global Geologic Map of Europa 

T. Doggett, P. Figueredo, R. Greeley, T. Hare, E. Kolb, K. Mullins, D. Senske, 

K. Tanaka, and S. Weiser 

A Global Geologic Map of Ganymede at 1:15M 
G.W. Patterson, J.W. Head, G.C. Collins, R.T. Pappalardo, L.M. Proctor, and 

 B.K. Lucchitta 

Global Geologic Mapping of Io: First Steps 

D.A. Williams, L. Keszthelyi, P. Geissler, W. Jaeger, and T. Becker 

Moon

The Lunar Geologic Mapping Program: Summer 2006 Status 

L.R. Gaddis, J.A. Skinner, Jr., T. Hare, K. Tanaka, B.R. Hawke, P. Spudis, B. 

Bussey, C. Pieters, and D. Lawrence 

The Comparison and Origin of Copernicus Rays: Implications for the CopernicanEratosthenian Boundary 

B.R. Hawke, T.A. Giguere, L.R. Gaddis, B.A. Campbell, D.T. Blewett, J.M. Boyce, 

J.J. Gillis-Davis, P.G. Lucey, C.A. Peterson, M.S. Robinson, and G.A. Smith 

Progress on Mapping the Copernicus 1:2,500,000-Scale Quadrangle on the Moon: Impact 

Crater Facies and Mineralogies 

J.A. Skinner, Jr., L.R. Gaddis, and K.L. Tanaka 

Mars

Geologic Mapping of the Highland/Lowland Boundary Zones: Eastern Hellas Planitia 

and Deuteronilus Mensae, Mars 

D.A. Crown, L.F. Bleamaster, and F.C. Chuang 

Mapping Margaritifer Terra: MTMS -15017, -20002, -20007, -20017, -20022, -25002, 

-25007 

C.M. Fortezzo, K.K. Williams and J.A. Grant 

Geologic Mapping of Olympus Mons Caldera, Mars, at 1:200K 

Peter J. Mouginis-Mark 

1:200K Geologic Mapping of the Martian Impact Crater Tooting 

Peter J. Mouginis-Mark 

Geologic Mapping Results of the Olympia Cavi Region of Mars (MTM 85200): Units 

and History 

J.A. Skinner, Jr., and K. Herkenhoff 

Geologic Mapping and Stratigraphy of North Polar Deposits on Mars: Preliminary 

Results 

K.L. Tanaka, K.F. Mullins, J.A. Skinner, Jr., J.A.P. Rodriguez, and C.M. Fortezzo 

Geologic Mapping of the Medusae Fossae Formation on Mars and the Northern Lowland 

Plains of Venus 

J.R. Zimbelman 
GEOLOGIC MAPPING OF V-11 SHIMTI TESSERA AND V-12 VELLAMO PLANITIA, VENUS 

 J.C. Aubele, New Mexico Museum of Natural History & Science, Albuquerque, NM jayne.aubele@ state.nm.us 

Plains terrain covers ~80% of the surface of 

Venus[1]; however, the mechanism(s) of formation and 

age(s) represented by the plains continue to be debated. 

While the plains are assumed to be volcanic in origin, 

with subsequent modification by tectonism, impact 

cratering, and aeolian processes [2], there is a paucity of 

large volcanic centers occurring within the lowland 

plains [1,3]. The volcanic edifices that do commonly 

occur are small, predominantly shield-type, volcanoes. 

These small volcanoes were first examined in 

detail using Venera 15/16 data by this author and 

colleagues [4]. Magellan data enabled this author and 

colleagues to classify their morphology, to recognize that 

they frequently occurred in clusters [5], and to first name 

these clusters “shield fields” [6]. Shield fields were 

interpreted to be similar to terrestrial volcanic fields, 

with associated material covering an area beyond the 

edifices. In many cases the stratigraphic relationships of 

these fields are uncertain, but some clearly post-date and 

some pre-date surrounding regional plains. 

Questions of plains formation can be tested by 

detailed mapping using Magellan SAR images and other 

Magellan data sets [7]. V-11 and V-12 were originally 

proposed for mapping under VDAP, in order to analyze 

the relationship of small volcanoes and lowland plains. 

Four possible stratigraphic models were anticipated to be 

tested: (1) small volcanoes are the source of local flows 

that form or resurface the plains; (2) small volcanoes and 

the plains formed simultaneously, which implies that the 

edifices are localized point sources within a larger 

extrusive mechanism; (3) small volcanoes predate most 

of the plains terrain, which implies an early small edifice 

building stage and subsequent change in eruption style; 

or (4) small volcanoes postdate most of the plains 

terrain, which implies a change in eruption style to late 

localized centers or regions of volcanism. 

Quadrangle V-12 was mapped (Fig.1), and 

reports were presented in the mid-late 1990s [8]. The 

reports included the description and interpretation of a 

new unit in V-12, the “shield plains” or “Akkruva shield 

plains,” designated as Psh in the preliminary map. The 

type example of this unit is located at Akkruva Colles, 

43N, 131.5E, and consists of an average density of small 

volcanoes numbering 4500/106

km2. Unit Psh exhibits 

consistent characteristics and stratigraphic relationships 

within V-12. It was interpreted as a distinctive plains 

unit erupted by, or in association with, small volcanoes, 

and a useful local to regional stratigraphic marker. 

Preliminary mapping of V-11 tested the significance and 

extent of the unit; it has been mapped over an area of 

2.3X106

km2 in V-11and V-12. 

Following the initial reports of the Akkruva 

shield plains, authors of other Venus quadrangles also 

identified and mapped similar shield plains or shield 

terrain [9] units. Some of these units have similar 

stratigraphic relationships to the Akkruva unit, for 

example in V-3, 4, 13, 23, 24, 54, 55, and 56 [10]; other 

mappers have found different stratigraphic relationships, 

for example in V-8 and V-20 [11]. A shield plains unit is 

included in the proposed global stratigraphy of Venus 

[12] and has been suggested to be a globally widespread 

unit [13]. It has also been described as a thin, 

discontinuous, mechanically coherent layer (shield 

paint), with map relations that are inconsistent with a 

global stratigraphy but, instead, provide evidence for a 

new model of plains resurfacing [9,14]. Others have 

described the small volcanoes as responsible for a large 

component of local-scale resurfacing throughout Venus 

geologic history [15]. 

V-11 and V-12 provided the original definition 

and type example of this unit, and although a decade has 

passed since the initial mapping (due to the abrupt end of 

the VDAP program and a change in job), it is clearly 

useful to provide a reviewed and published map interpretation of this unit. While it may not provide the final, 

definitive answer, it is anticipated that geologic maps of 

V-11 and V-12 will provide additional data to better 

understand (1) differences and similarities of shield 

fields and shield plains, (2) stratigraphic relationships 

and regional extent of the Akkruva shield plains, and (3) 

possible significance of the Akkruva shield plains for 

style of volcanism and resurfacing. The steps needed for 

completion are: (1) complete detailed mapping of V-11; 

(2) revise V-12 geologic map as needed based on contact 

relationships with V-11 and with adjoining published 

maps; (3) finalize description of units and accompanying 

text for both maps; and (4) submit both maps for review 

by the end of the 2006 calendar year. 

[1] Guest et al (1992) JGR 97. [2] Squyres et al (1992) JGR 97; Arvidson 

et al (1992) JGR 97; Greeley et al (1992) JGR 97; Campbell et al (1992) 

JGR 97. [3] Head et al (1992) JGR 97, 13153; Crumpler et al (1989) Sci 

246, 273. [4] Aubele&Slyuta (1990) EMP, 50/51, 493; Garvin&Williams 

(1990), GRL17, 9, 1381. [5] Aubele (1993) LPSC24, 47; Crumpler et al 

(1997) in Venus II UofA Press; Crumpler&Aubele (2000) in H. Sigurdsson 

et al Encyl of Volcanology Academic Press. [6] Aubele&Crumpler (1992) 

International Colloquium on Venus, LPI Contrib. 789. [7] Tanaka et al 

(1993) Venus Geol Mappers Handbk, Open-file 93-516; Tanaka et al (1997) 

Venus II. [8] Aubele (1997) GSA Abst. 29, no. 6, A-138; Aubele (1996) 

LPSC 27, 49; Aubele (1995) LPSC 26, 59; Aubele (1994) LPSC 25, 45; 

Aubele (1993) GSA Abst. 25, A-221. [9] Hansen (2005) GSA Bull 117, 

no.5/6. [10] Bridges & Mercer (2002) LPSC 33; Lang&Hansen (2003) 

LPSC 34; Young&Hansen (2003) USGS I-2783; Ivanov&Head (2006) 

LPSC 37; Ivanov&Head (2001) USGS I-2684; Ivanov&Head (2003) USGS 

I-2792; Ivanov&Head (2005) USGS I-2870. [11] Addington (1999) LPSC 

30; McGill (2000) USGS I-2637. [12] Basilevsky&Head (2002) Geology 

30, 1015; Basilevsky&Head (2000) PlanSpSci 48. Basilevsky&Head (1998) 

JGR 103, 8531; Head & Basilevsky (1998) Geology 26, 35. [13] 

Kortz&Head (2002) LPSC 31; Ivanov&Head (2004) JGR 109, E10. [14] 

Hansen (2003) LPSC 34. [15] Stofan et al (2004) LPSC 35. 

GEOLOGIC MAPPING OF THE BETA REGIO QUADRANGLE (V-17), VENUS: CONSTRAINTS ON 

BETA RISE EVOLUTION. Alexander T. Basilevsky, Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 119991 Moscow, Russia and Department of Geological Sciences, Brown University, Providence, RI 02912, USA, atbas@geokhi.ru; Alexander_Basilevsky@Brown.edu. 

Summary: Geologic mapping of the V-17 quadrangle, which includes a significant part of the Beta 

Regio domical topographic rise (considered to be 

driven by mantle plume) and the analysis of the mapping results revealed the sequence of geologic units 

and structures and their relations to the rise. We show 

evidence that the Beta uplift started closely before the 

emplacement of psh/pwr regional plains whose global 

mean age is close to the mean surface age of the planet 

T = 300 m.y. to 1 b.y. [11]. The rise was continuing up 

to the recent time suggesting that the plume was active 

for several hundreds of millions of years and may be 

active now. 

Introduction: This study is based on the results of 

the geologic mapping of the V-17 quadrangle (25-

50o

N, 270-300oE), which includes a significant part of 

Beta Regio and the adjacent areas. This project used 

the traditional methods of geologic unit definition and 

characterization for the Earth [e.g., 1] and planets [e.g., 

13] modified for radar data [12]. Presented here are the 

results of the map revision resubmitted to USGS in 

May 2006. 

The mapped units: In the V-17 quadrangle there 

were mapped 8 geologic material units, dividing two 

of them into subunits, and three tectonic units. Their 

morphology and age sequence are shown in Figure 1. 

Tessera material (tt) is the oldest unit in the quadrangle. It is relatively radar bright, characterized by at 

least two sets of intersecting ridges and grooves resulting from tectonic deformation of some precursor terrain and is embayed by most of the other units. 

Densely fractured plains material (pdf) has rather 

flat surfaces, cut by swarms of subparallel lineaments, 

sometimes resolved as fractures. The general flatness 

of unit outcrops suggests that it was plains, probably 

made of mafic lavas [see e.g., 3]. 

Fractured and ridged plains material (pfr) is medium-bright with a predominantly smooth surface suggesting that it is composed of mafic lavas. The pfr unit 

is commonly deformed by broad ridges, forming ridge 

belts. 

Shield plains material (psh) is of intermediate radar 

brightness and characterized by abundant shields interpreted to be of volcanic origin [e.g., 8]. Typically 

shield plains are embayed by plains with wrinkle 

ridges and are wrinkle ridged, but in a few places, 

separate shields and shield clusters are superposed on 

wrinkle ridges. 

Wrinkle ridged plains material (pwr) is represented 

by plains material of intermediate-low to intermediatehigh radar brightness complicated by narrow wrinkle 

ridges. The volcanic (lava) origin of the pwr plains 

globally and within V-17 is supported by flow-like 

morphology of one of the subunits of this unit and by 

presence of the lava channels [8]. The pwr unit was 

subdivided into four subunits: the age sequence of 

pwr1, pwr2 and pwr3 plus pwru – undivided. Pwr and 

psh plains are often called altogether regional plains. 

Figure 1. Stratigraphic column for the V-17 Beta Regio 

quadrangle. Unit cdp (material of dark parabola craters) was 

not found within the quadrangle but some parts of ps, pl and 

rt units may be contemporaneous to cdp. 

Smooth plains material (ps) is radar dark and morphologically smooth. It is observed in the form of 

fields typically of irregular outlines and tens of kilometers across. Similar fields have been interpreted by 

[8] as flows of very liquid lava. 

Lobate plains material (pl) is mostly radar bright. 

Their prominent flow-like texture and association with 

obvious volcanic constructs prove that unit pl is composed of lavas [8]. 

Impact crater material unit (C). Within the V-17 

quadrangle there are 25 impact craters. They were subdivided into three age subunits: a lower one (C1) – 

pre-regional plains (pwr+psh) craters (crater Aigul); a 

middle one (C2) – post-regional plains craters with 

faint or no associated radar-dark halo (12 craters); and 
an upper one (C3) - post-regional plains craters with 

clear halo (12 craters). 

Within the V-17 quadrangle there were identified 

three tectonic units. The places saturated with young 

post-pwr fractures and graben have been mapped as 

tectonic unit of rifted terrain (rt), mostly in the N-S 

axial zone of the Beta rise. Fractures and graben of the 

rt unit deform all materials including the youngest ps 

and pl units, but locally are flooded by the pl lavas. 

Within V-17 there are linear zones saturated with 

faults distinct from those of rt unit in morphology 

(Figure 1) and in age. They have been mapped as a 

tectonic unit of fracture belts (fb) and are considered as 

close in origin to the rt zones [6, 7]. The fb faults cut 

units tt, pdf and pfr and are embayed by units psh and 

pwr, although some of fb faults cut psh and pwr. 

In several places of the V-17 quadrangle, there are 

areas of terrain resembling tessera in morphology. It is 

formed at the expense of fracturing of the material 

units pfr and pdf. In contrast to units rt and fb, this 

type of terrain typically forms equidimensional areas. 

Following [9] we mapped these areas as a tectonic unit 

of tessera transitional terrain (ttt). 

Spatial distribution of units and structures:

Based on the mapping results, we have analyzed the 

distribution and trends of different units and structures. 

It was found that tt, pdf, pfr and ttt structures show no 

correlation with the Beta rise planimetric geometry but 

next in time sequence, fb unit forming, in particular, 

the Agrona Linea belt and its structures do show the 

alignment. This is considered as the first morphologic 

signature of the initiation of the Beta uplift. Formed 

next in time, pwr plains obviously avoid the Beta rise 

thus confirming that it was already an upland area. 

However, the wrinkle ridge network, formed next, 

does not show a clear alignment with the Beta geometry, probably suggesting that the rise at that time was 

not sufficiently high to form the topographic load 

which could control the wrinkle ridge orientation. 

Dating the Beta activity using the degree of crater dark halo preservation: This was done through 

analysis of age relations of four impact craters with pl 

lavas and rt faults. The craters are: 1) crater Sanger 

(33.8o

N, 288.6oE, D = 84 km), has a clear dark halo 

and its ejecta outflows are cut by faults branching from 

the Devana Chasma rift; 2) crater Raisa (27.5o

N, 

280.3o

E, 13.5 km), has a faint halo (FH) and is partly 

flooded by Theia Mons pl lavas; 3) the FH crater Olga 

(26o

N, 284oE, 15.5 km), superposed on some rt faults 

and cut by others; and 4) FH crater Tako (25o

N, 285oE, 

11 km), superposed on pl lavas associated with a 

branch of Devana Chasma rift. A number of authors 

[2, 5, 6, 10] showed that craters with faint or no associated dark halo formed within the first part of the 

post-regional plains time period T, while craters with 

clear dark halos, within the second part of it, but earlier than 0.1-0.15T ago. So the described relations 

suggest that the Theia Mons pl volcanism and the 

Devana Chasma rt rifting were active at least within 

some period of time between T and 0.5T ago, and that 

the rifting continued, at least, into the time between 

0.5T to 0.1-0.15T ago. 

Beta Regio evolution: Analysis of the mapping 

results permitted the construction of a scenario of Beta 

Regio evolution shown in Figure 2: 

Figure 2. A diagram showing evolution of the Beta Regio 

rise. 

References: [1] American Commission on Stratigraphic Nomenclature, 1961, Amer. Ass. Petrol. Geol. 

Bull., 45, 645-665. [2] Arvidson, et al., 1992, JGR, 

97, 13,303-13,318. [3] Basilevsky & Head, 2000, PSS, 

48, 75-111. [4] Basilevsky & Head, 2000, JGR, 105, 

24,583-24,611. [5] Basilevsky & Head, 2002, JGR, 

107, doi 10.1029/2001JE001584. [6] Basilevsky et al., 

2003, JGR doi:1029.2003GL 017504. [7] Hansen et 

al., 1997, in Venus II, Univ. Arizona Press, p. 797-

844. [8] Head et al., 1992, JGR, 97, 13,153-13,197. [9] 

Ivanov & Head 2001, JGR, 106, p. 17,515-17,566. 

[10] Izenberg et al., 1994, GRL 21, 289-292. [11] 

McKinnon et al., 1997, in Venus II, Univ. Arizona 

Press, p. 969-1014. [12] Tanaka, K.L. (compiler), 

1994, Venus geologic mappers' handbook, second edition: U.S. Geological Survey Open-File Report 94-

438, 50 p. [13] Wilhelms, D.E., 1990, Geologic mapping, in Planetary Mapping: New York, Cambridge 

University Press, p. 208-260. 
PRELIMINARY REPORT ON GEOLOGIC MAPPING OF ISABELLA QUADRANGLE (V-50) AND 

HELEN PLANITIA, VENUS. Leslie F. Bleamaster III, Planetary Science Institute, 3635 Mill Meadow Dr., San 

Antonio, TX 78247, lbleamas@psi.edu. 

Introduction: New funding (start 04.15.06) 

supports geologic mapping efforts of Isabella 

Quadrangle (1:5M) (Figure 1a.) and Helen Planitia 

(1:10M) (Figure 2). Data downloads from the USGS 

are complete for Isabella and continue for Helen 

Planitia (approximately 30 GB in total). The 

remainder of year one will build upon completed 

reconnaissance mapping [1] with the definition and 

description of map units (DOMU) and construction 

of the sequence of map units (SOMU) and geologic 

history. By the end of year two, Isabella Quadrangle 

will be submitted for review and mapping of Helen 

Planitia will begin. Year three will be devoted to 

completing the synthesis map of Helen Planitia. 

1b.

1c.

contractional features

shields

coronae/paterae

quasi-circular feature ,

not impact crater

1a.

Geologic areas and motivation: The Isabella 

Quadrangle (25-50°S, 180-210°E) lies to the south of 

the eastern extent of the Diana-Dali Chasmata system 

and Atla Regio, which contains the volcanoes Sapas, 

Maat and Ozza Montes. Isabella Quadrangle is host 

to numerous coronae and small volcanic centers 

(paterae and shield fields) (Figure 1b.), focused 

(Aditi and Sirona Dorsa) and distributed (penetrative 

north-south trending wrinkle ridges) contractional 

deformation, and radial and linear extensional 

structures (Figure 1c.), all of which contribute 

materials to and/or deform the expansive surrounding 

plains (Nsomeka and Wawalag Planitiae). Specific 

questions posed for geologic mapping of the V-50 

quadrangle include: a) what and where are the source 

locations for the regionally dominant plains materials 

(e.g., coronae, paterae, shield fields, rifts and 

fissures)? b) what is the relationship, if any, between 

focused (deformation belts) and distributed (wrinkle 

ridges) contractional strain and local/regional 

volcanism? c) what role does structural reactivation 

play in deformation belt and wrinkle ridge 

development? 

The second map to be constructed through this 

effort is Helen Planitia (0-57°S, 180-300°E), which 

encompasses over 70 million square kilometers 

(including V-50), displays ~10km of relief, and 

potentially spans the entirety of Venus’ limited 

preserved geologic history as determined by Average 

→Figure 1a. Synthetic aperture radar (SAR) 

mosaic of Isabella Quadrangle (V-50); 25-50°S, 

180-210°E. Preliminary mapping shows spatial 

distribution of large- and small-scale volcanic 

centers (1b) and deformation (1c). 

extensional features
Surface Model Ages (ASMA) [2, 3]. This area 

affords the opportunity to study local relationships of 

a series of volcano-tectonic features across several 

physiographic provinces. Motivation for mapping in 

Helen Planitia includes assessment of a) resurfacing 

styles with respect to transitions from the highlands 

to the lowlands, b) changes in surface morphology of 

volcano-tectonic features across physiographic 

regions that may represent crustal/lithospheric 

heterogeneities, c) local timing relationships and their 

regional significance, d) the spatial and temporal 

relationships between craters with outflows and 

volcanic constructs, and to what extent are crater 

outflows directly related to impact processes versus 

post-impact modification, and e) various mapping 

methodologies and techniques. 

Mapping: Preliminary mapping of V-50 has 

begun with the demarcation of major structural and 

morphologic features including both primary features 

(flow fronts, impact craters) and secondary features 

(wrinkle ridges, fractures) (Figure 1b and 1c) in a 

reconnaissance mode. This approach avoids the 

often-frustrating task of drawing the first unit contact, 

and although secondary structures do not define 

geologic units, they do provide a good first-sense of 

crosscutting and embayment relationships while one 

achieves a deeper appreciation of all the datasets. 

Adobe Illustrator currently serves as the primary 

mapping environment; datasets have been placed into 

several georectified layers with varying degrees of 

transparency. Reconnaissance mapping (please see 

poster) will soon be followed by the delineation and 

description of geologic units incorporating 

topography, reflectivity, and emissivity. 

References: [1] Bleamaster, L.F. III, (2006) 

LPSC XXXVII abstract #2233. [2] Phillips and 

Izenberg (1995) Geophys. Res. Lett., 22, 1517-1520. 

[3] Hansen and Young (in press), GSA special 

volume in honor of Gary Ernst. 

Figure 2. Altimetric radar image map and prominent geographic feature names of the Helen Planitia Regional 

Study Area (I-2477) to be mapped at 1:10M scale. Red lines demark 1:5M scale quadrangle boundaries. 
GEOLOGIC MAPPING OF THE GUINEVERE PLANITIA QUADRANGLE OF VENUS. David A. Crown1

and Ellen R. Stofan2

, 1Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, 2Proxemy 

Research, P.O. Box 338, Rectortown, VA 20140, crown@psi.edu.

Introduction. The Guinevere Planitia (V-30) 

quadrangle of Venus (0-25°N, 300-330°) covers a 

lowland region east of Beta Regio and west of Eistla 

Regio and includes parts of Guinevere and Undine 

Planitiae. The V-30 quadrangle is dominated by lowlying plains interpreted to be of volcanic origin and 

which exhibit numerous wrinkle ridges. Using Pioneer 

Venus, Goldstone, and Arecibo data, previous 

investigators have described radar bright, dark, and 

mottled plains units in the Guinevere Planitia region, as 

well as arcuate fracture zones and lineament belt 

segments that define the Beta-Eistla deformation zone 

[1-5]. Magellan SAR images reveal that volcanic 

landforms compose the majority of the surface units in 

the quadrangle [6-7]. The V-30 quadrangle contains 

parts of four major volcanoes: Atanua (9°N, 307°), 

Rhpisunt (3°N, 302°), Tuli (13°N, 314°), and Var (3°N, 

316°) Montes, and three coronae: Hulda (12°N, 308°), 

Madderakka (9°N, 316°), and Pölöznitsa (1°N, 303°). 

Seymour crater, located at 18°N, 327°, is associated 

with extensive crater outflow deposits. 

Project Overview. Preparation of the geologic 

map of the V-30 quadrangle includes analysis of 

Magellan data, including synthetic aperture radar 

(SAR) images and altimetry, roughness, reflectivity, 

and emissivity data sets. Full-resolution Magellan 

image mosaics (FMAPs) and synthetic parallax stereo 

images produced by the U.S. Geological Survey are 

key mapping products for unit characterization and 

determination of stratigraphic relationships. 

Initial support for production of the geologic map 

was provided by a NASA Venus Data Analysis 

Program (VDAP) grant (1993-1994), which also 

included morphologic and radar remote sensing 

analyses of venusian steep-sided domes and terrestrial 

silicic domes as potential analogues [8-10]. Subsequent 

analyses of the morphologic and radar backscatter 

properties of lava flows associated with volcanoes in 

Guinevere Planitia have also been conducted [11]. 

Mapping work completed under VDAP support 

included completion of a preliminary geologic map of 

the entire quadrangle [6-7]. This map was prepared by 

hand on an early SAR base of incorrect scale. Current 

tasks include compilation of the map in digital form on 

the 1:5M base, and, during the digitization process, a 

reassessment of unit contacts using synthetic stereo 

data, which was not available when the original draft of 

the map was prepared. 

Scientific objectives for mapping the Guinevere 

Planitia quadrangle include: 1) documenting the 

evolutionary stages of shield volcanoes, 2) evaluating 

the geologic context for steep-sided dome formation, 

and 3) assessing spatial and temporal relationships 

between volcanic and tectonic features. Mapping will 

provide a synthesis of the geologic and volcanic 

histories of Guinevere Planitia and assess their 

implications for the evolution of venusian lowland 

plains and styles of venusian volcanism. 

Mapping Results. Mapping completed to date has 

defined four main types of geologic units in the V-30 

quadrangle: flow materials, plains materials, tesserae 

and other highly tectonized units, and crater materials. 

Scattered throughout the map area are embayed 

remnants of intensely deformed materials; some of 

these show two or more tectonic fabrics (tesserae) and 

others show one dominant orientation of lineaments. 

The extensive volcanic plains evident across the 

quadrangle have been divided into two units. Mottled, 

lineated plains are generally large expanses containing 

a variety of small volcanic domes, cones, shields and 

flows. Zones of tectonic disruption are common. 

Smooth plains are low-lying regions that exhibit 

uniform radar brightness over large distances. Flow 

margins can be identified, but small volcanic edifices 

are not abundant. Fractures and ridges are common. 

Typically, volcanic flows are superposed on the plains; 

locally plains may embay the flanks of the major 

volcanoes in the map area. 

Volcanic flow materials in the V-30 quadrangle 

have been divided into two major morphologic types. 

Plains-forming flow materials are extensive, radar 

bright or dark, relatively flat-lying sheets and can 

extend for hundreds of kilometers from their apparent 

source vents. Lobate flow materials are narrow, 

sinuous, overlapping radar bright and dark deposits 

with lobate margins that form radial patterns around 

their source vents; lobate flow materials have 

accumulated to form the surfaces of the major 

volcanoes in the map area. Numerous small domes, 

cones, and shields are observed in association with 

lobate flow materials on these large volcanoes. 

Structural features observed in Guinevere Planitia 

include wrinkle ridges, fractures, and lineaments found 

primarily in plains units, coronae and corona-like 

structures, and tesserae and other highly tectonized 

units. In the plains, structures exhibit a diversity of 

orientations and occur in sets of features with similar 

trends. Prominent E-W and SE-NW trends are 

observed in the smooth plains at the eastern margin of 

the V-30 quadrangle. 

References: [1] Campbell, D.B. et al. (1989), Science, 

246, 373-377. [2] Arvidson, R.E. et al. (1990), in Proc. 

Lunar Planet. Sci. Conf., 20th, 557-572. [3] Senske, D.A. 

(1990), Earth, Mons, and Planets, 50/51, 305-327. [4] 

Senske, D.A. et al. (1991), Earth, Moon, and Planets, 55, 

163-214. [5] Stofan, E.R. et al. (1990), Lunar Planet. Sci. 

Conf., XXI, 1208-1209. [6] Crown, D.A. et al. (1993), 

Lunar Planet. Sci. Conf., XXIV, 355-356. [7] Crown, D.A. 

et al. (1994), Lunar Planet. Sci. Conf., XXV, 301-302. [8] 

Anderson, S.W. et al. (1998), Geol. Soc. Am. Bull., 110, 

1258-1267. [9] Stofan, E.R. et al. (2000), J. Geophys. Res., 

105, 26,757-26,771. [10] Plaut, J.J. et al. (2004), J. 

Geophys. Res., 109 E03001, doi:10.1029/2002JE002017. 

[11] Byrnes, J.M. and D.A. Crown (2002), J. Geophys. 

Res., 107 (E10), 5079, doi:10.1029/2001JE001828. 
MAPPING IN THE FREDEGONDE (V-57) QUADRANGLE, VENUS: PRELIMINARY RESULTS. M.A.

Ivanov1,2 and J.W. Head2 ,

 1Vernadsky Institute, RAS, Moscow, Russia, mikhail_ivanov@brown.edu, 2 Brown University, Providence, RI, USA, james_head @brown.edu.

Introduction: Midlands (0-2 km above MPR,

[1,2]) constitute the most significant topographic

province on Venus (~80%) and host the richest variety

of terrains, units, and structures. The character of transition from the midlands to both the lowlands and

highlands and the distribution and sequence of units

and structures in the midlands are crucially important

in understanding of modes and timing of formation of

this topographic province. Many workers have documented the wide range of features that are seen in the

midlands [3-12].

The Fredegonde (V-57) quadrangle in the southern

hemisphere of Venus is a typical region of midlands

that exposes abundant features characterizing this

province and contacts with the upland of Lada Terra to

the west and the lowland of Aino Planitia to the northeast. Here we report on the preliminary results of geologic mapping in the V-57 quadrangle and describe

major features, units, and structures exposed in the map

area, and outline the main episodes of the geologic

history of this region.

Regional setting and major geologic and topographic features: The area of the Fredegonde quadrangle (50-75o

S, 60-120oE, Fig.1) covers the eastern midland portion of Lada Terra. The most prominent features in the map area are linear deformational zones

consisting of large coronae interconnected by swarms

of grooves and graben. There are two such zones. The

largest is in the central portion of the quadrangle. It is

several thousands of km long, oriented in the northern

direction, and includes four coronae. The second zone

is in the northwestern corner of the map area. It is oriented in NE direction, consists of Geyaguga and

Xaratanga Chasmata, and includes two coronae. Less

abundant are fragments of belts of ridges that have a

general NW trend and occur in the central longitudinal

area of the quadrangle. Topographically, both the corona-groove chains and belts of ridges represent broad

(up to 100s km wide) ridges 100s m (up to a kilometer)

high. Relatively small (100s km across, 100s m deep)

equidimensional basins of Mugazo, Alma-Merghen,

and Laimdota Planitiae occur between the coronagroove-chains in the west and border the central chain

from the east. The corona-groove chains resemble in

many aspects the corona-rift zones at the margins of

large equidimensional basins such as Lavinia (V-55)

and Atalanta (V-4) Planitiae [13,14].

Material and structural units and their relationships: During our reconnaissance mapping we have

defined three groups of material and structural units

(Fig.2). (I) The oldest units: densely lineated plains

(pdl), ridged plains (pr), and groove belts (gb). Unit pdl

occurs as small outliers in the central area of the quadrangle. Ridged plains are exposed in fragments of the

belts of ridges. Groove belts consist of dense swarms

of fractures and graben and form the corona-groove

chains. All units of this group form either local (pdl) or

regionally important highs (pr and gb) and are embayed by vast plains units of group II. (II) Units of the

middle stratigraphic level, shield plains (psh) and regional plains (rp), cover the major portion of the quadrangle. Shield plains are characterized by abundant

small shield- and cone-like features (small volcanoes

[15-17]) that give the unit a distinctly hilly texture. The

volcanoes appear to be sources of the adjacent plains

material. Regional plains have a morphologically

smooth surface and uniform radar backscatter. Sources

of the plains are not obvious. Wrinkle ridges deform

both units of this group and sometimes occur in the

older units. Shield plains and regional plains occur at

relatively low topographic levels and fill the equidimensional basins. (III) Units that form the top of the

regional stratigraphic column: smooth plains (ps), and

lobate plains (pl). Smooth plains have uniform and

preferentially low radar albedo and lobate plains are

characterized by lobate and digitate boundaries. Both

units are tectonically undeformed and embay most

tectonic structures including wrinkle ridges. Lobate

plains are spatially associated with some coronae of the

corona-groove chains, flow down the regional slopes

and partly fill the basin-like topographic lows.

Summary: The results of preliminary mapping in

the V-57 quadrangle allow us to outline the major episodes of the geologic history of this region. Tectonics

apparently played the most important role in the beginning of the history. The majority of tectonic deformation occurred early on and was related to the formation

of linear deformational belts, the most prominent of

which are the corona-groove chains. During this period, the most important topographic features (broad

linear ridges and equidimensional basins) of the midland portion of Lada Terra were formed. During the

middle and late periods, volcanism was more important

and vast plains moderately deformed by tectonic

structures were emplaced. There is a little evidence

suggesting a continued development of the major topographic features during the middle stages of the

geologic history of the region. The flow direction of

lobate plains (from the broad ridged toward the floor of

the basins) suggests that the overall topographic configuration of the midlands within the map area was

established prior to emplacement of the youngest volcanic plains. The main topographic and structural elements of coronae in the region were formed before
FREDEGEONDE (V-57) QUADRANGLE, VENUS: M. A. IVANOV AND J. W. HEAD

emplacement of both shield plains and regional plains.

The youngest lobate plains, however, typically are associated with some coronae. This means that the corona structures were either reactivated late in the geologic history or volcanic activity at coronae was delayed until the late stages of history.

References: 1) Masursky, H., et al., JGR, 85, 8232, 1980, 2)

Pettengill, G.H., et al., JGR, 85, 8261, 1980, 3) Ford, P.G.

and G.H. Petttengill, JGR, 97, 13103, 1992, 4) Barsukov,

V.L., et al., JGR, 91, D399, 1986, 5) Frank, S.L. and J.W.

Head, EMP, 50/51, 421, 1990 6) Basilevsky, A.T. and J.W.

Head, PSS, 48, 75, 2000, 7) Basilevsky, A.T. and J.W. Head,

JGR, 105, 24583, 2000, 8) Stofan, E.R., et al., Icarus, 152,

75, 2001, 9) Bleamaster, L.F. and V.L. Hansen, JGR, 109,

doi: 10.1029/2003JE002193, 2004, 10) Nunes, D.C., et al.,

JGR, 109, doi: 10.1029/2003JE002119, 2004, 11) Young,

D.A. and V.L. Hansen, JGR , 110, doi:

10.1029/2004JE001965, 2005, 12) Herrick, R.R., et al., JGR,

110, doi: 10.1029/2004JE002283, 2005, 13) Ivanov, M.A.

and J.W. Head, USGS Map I-2684, 2001, 14) Ivanov, M.A.

and J.W. Head, USGS Map I-2792, 2004, 15) Aubele J.C.,

LPSC XXVI, 59, 1995, 16) Addington, E.A., Icarus, 149, 16,

2001, 17) Ivanov, M.A. and J.W. Head, JGR, 109, doi:

10.1029/2004JE002252, 2004.

Figure 1. Major features in the V-57 quadrangle.

Figure 2. Preliminary sketch map of the V-57 quadrangle.
GEOLOGIC HISTORY OF THE LAVINIA PLANITIA / LADA TERRA REGION, VENUS: RESULTS OF THE MAPPING IN 

THE V-55, V-61, AND V-56 QUADRANGLES, M.A. Ivanov1,2 and J.W. Head2

,

 1Vernadsky Institute, RAS, Moscow, 

Russia, mikhail_ivanov@brown.edu; 2

Brown University, Providence, RI, USA, james_head@brown.edu 

1. Introduction: Lada Terra is a region of midlands (0-

2 km above mean planetary radius, MPR) at high southern latitudes (~300-90o

E, 55-80oS, covered by the V-61 

and V-56 quadrangles). It is characterized by a large 

dome-shaped structure, a swell. Lada Terra hosts numerous coronae, including Quetzalpetlatl (~800 km 

across) and Boala Coronae [1,2], and large complexes 

of lava flows, fluctūs, emanating from several distinct 

centers [3,4]. Belts of fractures and graben interconnect 

many coronae in Lada Terra [5]. The vast lowland of 

Lavinia Planitia (~330-0o

E, 25-55oS, V-55 quadrangle) 

is adjacent to Lada Terra to the north. Deformational 

belts of ridges and grooves and vast moderately deformed plains characterize the floor of Lavinia Planitia 

[6,7]. The pattern of deformation, topography, and gravity signature are consistent with mantle downwelling 

under Lavinia Planitia [8] and with mantle upwelling in 

the region of Lada Terra [9,10]. Thus, Lada Terra and 

Lavinia Planitia appear to represent contrasting geodynamic provinces. Their close proximity suggest a genetically linked history [4]. We studied these regions in 

detail during geological mapping at 1:5 M scale under 

the USGS planetary mapping program (combined area 

of the quadrangles V-55 [11], V-56, mapping in progress, and V-61, map in edit). The major goal of our 

study was to reconstruct the major episodes of geologic 

history of Lada and Lavinia and establish the timing and 

sequence of events during formation and evolution of 

these regions.

2. Topographic configuration of Lavinia Planitia 

and Lada Terra: Lavinia Planitia is a large lowland (a 

basin) a few thousands of km across, which is as deep as 

~1.5 km below MPR. The general distribution of topography in Lavinia Planitia is asymmetric. The deepest 

portion of the basin is shifted toward its southern edge. 

Toward the north and northwest, the elevation changes 

~1 km over a distance of ~1800 km while at the southern and eastern margins the same change in elevation 

occurs over a distance of ~500 km. Deformational belts 

on the floor of the basin form a radial pattern and topographically represent elevated zones several hundred 

meters high. The most prominent belts are concentrated 

in the deepest area of Lavinia Planitia. The major portion of Lada Terra is within the 0-2 km interval (midlands). The largest topographic feature of Lada Terra is 

a broad (~1000 km across) symmetric swell, the summit 

of which reaches an elevation of ~3.5 km. The overall 

topographic shape of the Lada swell resembles that of 

the other dome-shaped rises on Venus such as Beta Regio or Eistla Regio. In contrast to these areas, which are 

topped by large volcanoes, the Lada swell hosts the 

nested Quetzalpetlatl and Boala Coronae and lacks large 

volcanoes. Two regional-scale topographic features 

(thousands of km long, hundreds of km wide, a couple 

of km in amplitude), an elongated depression, and a 

topographic ridge, concentrically outline the swell of 

Lada from the north and east. 

3. Regional geology: Units, structures, and their 

stratigraphic relationships: In our mapping, we used 

traditional methods of unit definition [12,13] appropriately modified for radar data [14]. We defined units and 

mapped relations between them and tectonic structures 

using F- and C1-MIDR images and altimetry data. The 

background for our mapping approach is described in 

[14-18]. 

3.1. Units All three mapped quadrangles display a 

similar set of material and tectonic units. Outcrop continuity and consistent age relationships among them allow stratigraphic correlations of the units in the broad 

mapped region. The oldest unit is Tessera. It has a 

unique pattern of deformation consisting of intersecting 

ridges and grooves [19-22, 7] and is consistently embayed by less deformed materials. The major occurrences of tessera in the area of our mapping are Alpha 

Regio (to the east of Lavinia Planitia) and Cocomama 

Tessera (to the east of the Lada swell). Densely lineated 

plains (pdl) form the oldest plains unit. Its surface is cut 

by densely packed lineaments (some of them are fractures). Material of densely lineated plains embays 

tessera where these units are in contact. Ridged plains 

(pr) are commonly deformed by broad (5-10 km wide) 

ridges tens of kilometers long. The ridges are arranged 

in linear belts and predominantly occur on the floor of 

Lavinia Planitia. Both emplacement and deformation of 

ridged plains postdate deformation of the unit pdl. 

Abundant small (a few km) shield-like features characterize Shield plains (psh). The unit occurs preferentially 

within Lavinia Planitia where it embays ridged plains. 

Psh is significantly less widespread within the elevated 

portion of Lada Terra where shield plains appear to be 

almost completely buried by younger plains. Regional 

plains (rp) form the most widespread unit with a morphologically smooth and homogeneous surface, which 

is typically cut by wrinkle ridges. Sources of the plains 

are not obvious. There are two units of regional plains. 

The lower unit (rp1) has relatively low radar backscatter 

and usually makes up the floor of the lowlands surrounding Lada Terra. Sometimes it occurs in stratigraphic windows on the slopes of the Lada swell. The 

upper unit (rp2) has a higher radar albedo and, sometimes, lobate boundaries. The unit occurs on the western 

slope of the Lada swell. Both units of regional plains 

embay shields plains. Lobate and digitate boundaries 

(Lobate plains, pl), morphologically smooth surfaces 

(Smooth plains, ps), and clusters of small shields 

(Shield clusters, sc) similar to those of shield plains 

characterize units that are younger than regional plains. 
M. A. IVANOV AND J. W. HEAD: LAVINIA/LADA TERRA REGION 

We also defined two tectonic units: Groove belts (gb) 

and Rift zones (rt). These are elongated belts of extensional structures thousands of km long and hundreds of 

km wide. Groove belts preferentially occur on the floor 

of Lavinia Planitia where they cut ridges of the unit pr 

and are embayed by shield plains and regional plains. 

Rift zones are concentrated in Lada Terra and appear to 

be contemporaneous with the youngest plains units (pl, 

ps, and sc). 

3.2. Structures There are two types, scales, and 

ages of contractional features in the map area. The older 

are ridges and arches that deform ridged plains (unit pr). 

Regional plains embay these structures. The northern 

rim of Quetzalpetlatl Corona is morphologically similar 

to a typical ridge belt, although it is unclear whether it is 

a fragment of regionally developed belts or it is related 

to the evolution of the corona. Regional plains embay 

the rim at its southern end. Thus, formation of the rim 

predates emplacement of regional plains. The younger 

contractional features are wrinkle ridges that form a 

regional network that deforms regional plains and other 

older units and are embayed by smooth and lobate 

plains. 

Numerous fractures and graben in the studied region are typically collected in zones of extensional 

structures (groove belts and rift zones). The largest of 

them is the rift-like zone of Kalaipahoa Linea (V-61) 

that outlines the Lada swell from the north. Another riftlike zone is within the V-56 quadrangle. It consists of a 

chain of coronae interconnected by graben and outlines 

the swell from the east. Within both zones there are 

prominent sources (coronae) from which emanate the 

youngest volcanic flows (e.g. Mylitta Fluctus). 

4. Discussion and conclusions: The V-55, V-61, 

and V-56 quadrangles cover a region that consists of 

two provinces, Lavinia Planitia and Lada Terra, contrasting in topography, gravity, and overall geologic 

history. Deformational zones of ridge and groove belts 

that form the bottom of the general stratigraphic column 

populate the floor of Lavinia Planitia. The most prominent belts preferentially occur at the deepest portion of 

the Lavinia basin and are embayed by units of intermediate stratigraphic position (psh and rp). An important 

characteristic of the basin is the absence of both young 

deformation and volcanic materials postdating formation of wrinkle ridges. The general topographic configuration of Lavinia Planitia and the radial pattern and topographic position of the deformational belts on its floor 

are consistent with the subsidence of the surface and 

formation of the Lavinia basin [8]. The stratigraphic 

position of the belts implies that the subsidence largely 

occurred relatively early on in the geologic history and 

the topographic asymmetry of Lavinia suggests that the 

locus of the subsidence was near the southern and eastern edges of the basin. The vast plains units of the intermediate stratigraphic position were emplaced on the 

floor of the already existing lowland. 

Lada Terra is in sharp contrast to Lavinia Planitia. 

It is an elevated region, which is dominated by the Lada 

swell and characterized by abundant young volcanism 

(lobate plains) and young extensional deformation (rift 

zones). The summit area of the swell (Quetzalpetlatl and 

Boala Coronae) and the Tarbell/Jord Coronae complex 

within the rift of Kalaipahoa Linea are the most important sources of young volcanism. Young lava flows flow 

down the regional slopes of the swell and the steeper 

southern and eastern edges of the Lavinia basin [11,23]. 

Magellan gravity data [24,25] show that the eastern half 

of the quadrangle, which corresponds to the Lada swell, 

is characterized by high values of both vertical gravity 

acceleration (up to 120 mGal) and height of geoid (up to 

40 m). These features collectively strongly suggest that 

the central portion of Lada Terra represents a region of 

mantle upwelling. The stratigraphic position of the most 

abundant units in Lada Terra means that the upwelling 

largely postdates the subsidence in Lavinia Planitia. 

Thus, the geologic history of the region of Lavinia 

Planitia and Lada Terra appears to consist of two major 

episodes. The earlier episode corresponds to formation 

of a vast basin in Lavinia. During a distinctly later episode a broad updoming, massive volcanism, and extensional tectonics occurred in Lada Terra. The close geographic position of Lavinia and Lada, their overall topographic configuration, and general sequence of events 

are consistent with a genetically linked evolution of 

these provinces. In this model, the downwelling in Lavinia may have provoked the upwelling under Lada and 

led to younger geologic activity in this region. 

References: [1] Stofan, E. R. et al. (1997) JGR, 97, 13347. [2] 

Crumpler, L. S. and J. Aubele, Volcanism on Venus, in: Encycl. of Volcanoes, 727, 2000, 3) Roberts, K.M., et al., JGR, 

97, 15991, 1992, 4) Magee, K.P. and J.W. Head, JGR, 100, 

1527, 1995, 5) Baer, G. et al., JGR, 99, 8355, 1994, 6) 

Squyres, S.W. et al., JGR, 97, 13579, 1992, 7) Solomon, 

S.C.et al., JGR, 97, 13199, 1992, 8) Bindschadler, D.L. et al., 

JGR, 97, 13495, 1992, 9) Kiefer, W.S. and B.H. Hager, JGR, 

96, 20947, 1991, 10) Simons, M., et al., GJI, 131, 24, 1997, 

11) Ivanov, M. A. and J. W. Head, USGS Geol. Inv. Ser., Map 

I-2684, 2001, 12) Code of Stratigraphic Nomenclature, 

AAPGB, 45, 645, 1961, 13) Wilhelms, D. E. Geologic mapping in: Planetary Mapping, 208, 1990, 14) Tanaka, K.L., 

Venus geologic mappers' handbook, USGS OFR 94-438, 50, 

1994, 15) Basilevsky, A. T. and J.W. Head, EMP, 66, 285, 

1995, 16) Basilevsky, A. T. and J.W. Head, PPS, 43, 1523, 

1995, 17) Basilevsky, A. T.et al., The resurfacing history of 

Venus in: Venus II 1047-1086, 1997, 18) Ivanov, M. A. and J. 

W. Head, JGR, 106, 17515, 2001, 19) Barsukov, V.L. et al., 

JGR, 91, D399, 1986, 20) Basilevsky, A. T., et al., JGR, 91, 

D399, 1986, 21) Bindschadler, D.L. and J.W. Head, JGR, 96, 

5889, 1991, 22) Sukhanov, A.L. In: Venus Geology, Geochemistry, and Geophysics, 82, 1992, 23) Bridges, N. T. and 

G. E. McGill, USGS Geol. Inv. Ser., Map I-2747, 2002, 24) 

Konopliv, A.S., et al., GRL, 20, 2403, 1993, 25) Konopliv, 

A.S. and W.L. Sjogren, Icarus, 112, 42, 1994. 
MAPPING OF THE V-7 QUADRANGLE: SEQUENCE OF EVENTS DURING FORMATION OF LAKSHMI PLANUM, VENUS,

M.A. Ivanov1,2 and J.W. Head2

, 1Vernadsky Institute, RAS, Moscow, Russia, mikhail_ivanov@brown.edu; 2 Brown 

University, Providence, RI, USA, james_head@brown.edu 

1. Introduction: The key feature of the Lakshmi 

Planum quadrangle (V-7, 50-75o

N, 300-360oE) is the 

volcanic plateau of Lakshmi Planum, which represents a 

unique class of highlands on Venus. The surface of Lakshmi Planum stands 3-4 km above mean planetary radius, MPR, and is surrounded by the highest Venusian 

mountain ranges that are 7-10 km high. Lakshmi 

Planum and its mountain surroundings are among the 

most intriguing features on Venus [1-7]. There are two 

alternative models of formation of the complex of Lakshmi Planum. In the first, this feature is considered as a 

result of mantle upwelling, formation, and collapse of a 

large dome [8,6,9,10]. In the second model, formation 

of Lakshmi Planum is explained by a mantle downwelling and collision of terrains against a foreland of the 

core region of Lakshmi [11-16]. The sequence of events 

during formation of Lakshmi plays a crucial role in the 

assessment of both models. For example, the collapse of 

a large dome would result in formation of chaotically 

oriented contractional structures in the interior of the 

plateau, suppressed volcanism there, and a general lateral progression of events in the direction from inside 

out. The alternative model would be consistent with the 

opposite direction of geologic activity, the older relative 

age of the mountain ranges, and younger volcanic activity in the central area of the plateau. 

In our mapping, we used traditional methods of unit 

definition [17,18] appropriately modified for radar data 

[19]. We defined units and mapped relations between 

them and tectonic structures using F- and C1-MIDR 

images and altimetry data. The background for our 

mapping approach is described in [19-23]. In this paper 

we describe the set of mapped units and structures and 

outline the apparent sequence of events during formation of Lakshmi Planum. 

2. Material units and structures: Although we 

have mapped tectonic structures independently of geologic units, sometimes the structures become a part of 

the definition of a unit. For example, tessera is analogous to Aureole member 4 of the Olympus Mons Formation on Mars [24]. In recently published Venus maps, 

the same approach was successfully applied in the mapping of several quadrangles [25-28]. Here we summarize the stratigraphic units and structures and their relations. 

2.1. Units. Tessera (t) appears to be the oldest material 

because it is embayed by most of the other units in the 

map area. Tessera is deformed by at least two sets of 

intersecting ridges and grooves, and is a result of tectonic deformation of some precursor terrain [3,4,29,30]. 

In the V-7 quadrangle, tessera is exposed inside and 

outside Lakshmi Planum. Densely lineated plains (pdl)

postdate tessera and form one of the oldest units. It has 

relatively flat surfaces and is cut by dense swarms of 

lineaments (fractures). Typically small patches of pdl 

occur outside Lakshmi Planum. Ridged plains (pr) are 

commonly deformed by relatively broad (2-5 km wide) 

ridges tens of kilometers long. In the V-7 quadrangle 

this unit is not abundant and occurs in the southern portion of the map area outside Lakshmi. Shield plains 

(psh) are characterized by abundant small shield-shaped 

features (2-20 km) interpreted to be small volcanoes. 

The unit is widely distributed in the quadrangle but occurs predominantly within the lowlands around Lakshmi 

Planum and is absent inside the plateau. Material of psh 

embays all previous units. Pitted and grooved material 

(pgm) is cut by narrow, wide, and shallow grooves with 

scalloped edges. In places, isolated pits and low shieldlike features are seen. The unit pgm occurs in four small 

areas at the periphery of the interior of Lakshmi in spatial association with the mountain ranges. Regional 

plains (rp) form the most widespread unit. The surface 

of it is smooth, homogeneous, and typically cut by 

wrinkle ridges. The sources of the unit are unknown. 

Regional plains occur both inside and outside Lakshmi 

Planum and cover the majority of the quadrangle. 

Lower unit of lobate plains (pl1) is also deformed by 

wrinkle ridges but has lobate boundaries and higher 

radar albedo than regional plains. The largest area of 

this unit is outside Lakshmi and a smaller occurrence of 

it is on the northern flank of Colette Patera inside the 

plateau. Smooth plains (ps) are characterized by uniform and preferentially low albedo. Material of unit ps 

embays wrinkle ridges. Small patches of ps are scattered 

throughout the map area. The largest occurrence of the 

unit is in the southern portion of Lakshmi Planum. Upper unit of lobate plains (pl2) is characterized by lobate 

flows that embay most tectonic structures including 

wrinkle ridges. There are three major occurrences of the 

unit: Neago Fluctūs and Djata Fluctus outside Lakshmi 

and Colette and Sacajawea Paterae inside the plateau. 

Impact craters (c) and crater outflow deposits (cf) are 

peppered throughout the quadrangle without any preferential concentrations.

2.2. Structures. Extensional structures. In many 

places, extensional structures are closely spaced and 

obscure underlying terrain. These concentrations consist 

of numerous fractures and graben and form linear belts 

(groove belts, gb) that are many hundreds of kilometers 

long and a few hundreds of kilometers wide. Groove 

belts are concentrated within the southern regional slope 

of Lakshmi Planum where they cut the units pdl and pr 

and are embayed by shield plains and regional plains. 

Contractional structures. Several types and scales of 

contractional features are observed within the quadrangle. Narrow and sinuous wrinkle ridges are seen 

throughout the quadrangle but are more abundant in vast 
M. A. IVANOV AND J. W. HEAD: LAKSHMI PLANUM REGION 

areas of regional plains. Broader and more linear ridges 

dominate ridged plains (pr), which are largely equivalent to the ridge belts of [31-32]. 

The most important occurrences of contractional 

structures in the map area are mountain belts (unit mt) 

surrounding the interior of Lakshmi Planum. Densely 

packed ridges that are 5-15 km wide and tens to a few 

hundreds of kilometers long characterize all belts. There 

are four such belts. Danu Montes (~100 km wide, 

~1000-1200 km long, and ~4-5 km high) border the 

southern edge of Lakshmi. Regional plains embay the 

ridges of Danu Montes on both sides of the mountain 

range. Akna Montes to the W of Lakshmi is a shorter 

(~800-900 km), wider (~200 km), and higher (~6-7 km) 

mountain range, which is slightly bent inside, toward 

the plateau of Lakshmi. Regional plains of the Lakshmi 

interior embay the innermost ridges of Akna Montes. At 

the outer side, ridges of Akna Montes deform the surface of pdl. Freyja Montes border Lakshmi Planum 

from the N and NE. This belt is wide (~300 km) and 

high (~6-7 km) and is characterized by complicated 

structure consisting of several domains with their own 

pattern of deformation. The massif of Freyja Montes 

appears to be embayed by regional plains of the Lakshmi interior. The northern edge of the belt is outside of 

the map area. Maxwell Montes are at the eastern edge of 

Lakshmi Planum. Within the map area, only the westernmost extensions of Maxwell are seen. Relationships 

of structures of Maxwell with the plains inside Lakshmi 

appear to be ambiguous and do not provide strong evidence suggesting relative ages of these units. 

3. Discussion and conclusions: The major goal of 

our mapping in the V-7 quadrangle was to establish the 

sequence of events during formation and evolution of 

Lakshmi. The main issues that we addressed in our 

study were: When were the mountain ranges formed? 

What is the nature of the Lakshmi interior? How do the 

interior and exterior regions of Lakshmi compare to 

each other? What is the general sequence of events during formation and evolution of Lakshmi Planum? There 

are three major physiographic provinces in the map 

area: the interior of Lakshmi Planum, the surrounding 

mountain ranges, and the exterior of Lakshmi. The sets 

of units and structures and their stratigraphic relationships are similar within the interior and exterior. This 

implies that similar processes in similar sequences have 

operated there and allows broad temporal correlations 

among mapped features. 

There is no compelling evidence suggesting when 

the mountain ranges formed relative to each other. It is 

possible, however, to establish the range of stratigraphic 

ages for the mountain belts as a class of features. The 

youngest unit deformed by structures of the mountain 

belts (Akna Montes) is pdl of Atropos Tessera. This unit 

establishes the lower stratigraphic limit of the belt formation. The oldest unit embaying structures of the 

ranges are regional plains inside and outside Lakshmi. 

Thus, the mountain crown of Lakshmi was formed relatively early on in the geologic history of the region. 

The interior of Lakshmi has a relatively simple 

stratigraphic record. The oldest unit exposed there is 

tessera, which is heavily embayed by regional plains. 

Large and small outliers of tessera are seen in many 

places of the interior suggesting that the thickness of 

regional plains is small. An important feature of the 

interior is the absence of ridge belts that indicates a virtual lack of contractional deformation there. Thus, the 

interior of Lakshmi appears to represent initially a 

tessera-like plateau that was geologically stable during 

formation of the mountain ranges. The youngest activity 

within the interior is related to volcanism and formation 

of the young plains ps, pl1, and pl2 sourced by Colette 

and Sacajawea Paterae. 

The exterior of Lakshmi displays abundant units and 

structures that predate regional plains (t, pdl, gb, pr, 

psh) suggesting that both volcanism and tectonics were 

concentrated predominantly outside the plateau during 

the earlier stages of the geologic history of the region. 

After formation of regional plains, volcanism through a 

few centers to the southeast and west of Lakshmi played 

the major role in the geologic history. 

The sequence of events during formation of the Lakshmi Planum and its surroundings suggests that these 

features began near the beginning of the observable 

geologic record. The general lateral progression of 

events appears to be oriented from outside in rather than 

in the opposite direction, which is consistent with the 

formation of the complex of Lakshmi Planum and the 

mountain ranges due to large-scale horizontal convergence, underthrusting, imbrication, and folding 

[13,14,16,33]. 

References: 1) Masursky, H., et al., JGR, 85, 8232, 1980, 2) Pettengill, 

G.H., et al., JGR, 85, 8261, 1980, 3) Basilevsky, A.T., et al., JGR., 91, 

D399, 1986, 4) Barsukov, V.L. et al., JGR, 91, D399, 1986, 5) Sukhanov, 

A.L., et al., USGS Map I-2059, 1989, 6) Pronin, A.A. In: Venus Geology, 

Geochemistry, and Geophysics, 68-81, 1992. 7) Kaula, W.M., et al., JGR., 

97, 16085, 1992, 8) Pronin, A.A., Geotectonics, 20, 271, 1986, 9) Grimm, 

R.E. and R.J. Phillips, GRL, 17, 1349, 1990, 10) Grimm, R.E. and R.J. 

Phillips, JGR, 96, 8305, 1991, 11) Vorder Bruegge, R.W. and J.W. Head, 

GRL, 16, 699, 1989, 12) Vorder Bruegge, R.W. and J.W. Head, Geology, 

19, 885, 1991, 13) Head, J.W., Geology, 18, 99, 1990, 14) Roberts, K.M. 

and J.W., GRL, 17, 1341, 1990, 15) Bindschadler, D.L., et al., GRL, 17, 

1345, 1990, 16) Keep, M. and V.L. Hansen, JGR., 99, 26015, 1994, 17) 

Code of Stratigraphic Nomenclature, AAPGB, 45, 645, 1961, 18) Wilhelms, D. E. Geologic mapping in: Planetary Mapping, 208, 1990, 19) 

Tanaka, K.L., Venus geologic mappers' handbook, USGS OFR 94-438, 50, 

1994, 20) Basilevsky, A. T. and J.W. Head, EMP, 66, 285, 1995, 21) 

Basilevsky, A. T. and J.W. Head, PPS, 43, 1523, 1995, 22) Basilevsky, A. 

T., et al., In: Venus II 1047-1086, 1997, 23) Ivanov, M. A. and J. W. Head, 

JGR, 106, 17515, 2001, 24) Scott, D.H., and Tanaka, K.L., USGS Map I1802-A, 1986, 25) Rosenberg, E. and McGill, G. E., USGS Map I-2721, 

2001, 26) Bridges, N. T., and McGill, G. E., USGS Map I-2747, 2002, 27) 

Campbell, B.A., and Campbell, P.G., USGS Map I-2743, 2002, 28) Hansen, V. L., and DeShon, H. R., 2002, USGS Map I-2752, 2002, 29) Bindschadler, D.L. and J.W. Head, JGR., 96, 5889, 1991, 30) Sukhanov, A.L. 

In: Venus Geology, Geochemistry, and Geophysics, 82, 1992, 31) Solomon, S.C., et al., JGR, 97, 13199, 1992, 32) Squyres, S.W. , et al., JGR, 

97, 13579, 1992, 33) Vorder Bruegge, R.W. and J.W. Head, EMP, 50/51, 

251, 1990. 
GEOLOGY OF THE JUNO CHASMA QUADRANGLE (V-47), VENUS, D. A. Senske, Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, 91109. 

Introduction. To understand how extension and 

volcanism are related both spatially and temporally, 

the region between latitudes 25° S and 50° S and longitudes 90° E and 120° E (Quadrangle V-47, Juno 

Chasma), is mapped [1,2] (Figure 1). In terms of 

large-scale structure and topography, the Juno region 

contains two distinct physiographic provinces: (1) the 

rolling lowlands of Aino Planitia that are located in the 

southern and western part of the map area and (2) the 

elevated linear topographic rise which runs approximately from east to west along the northern part of the 

quadrangle. Altimetry measurements show this area to 

reach an elevation of 1.0 km above the surrounding 

plains. Located along the crest of the highest topography is a 60- to 90-km wide, 1.0- to 2.5-km deep, graben, Juno Chasma. 

Geologic Units. Within the Juno Chasma region, 

nine geologic material units are identified and mapped 

[3] (Figure 1). The definition of each unit is based on 

an evaluation of relative variations and patterns of radar backscatter and the presence of crosscutting and 

on-lapping relations. The units are divided into four 

main classes, (1) those that form relatively localized 

systems of lava flows, (2) regional-scale plains forming materials, (3) tectonic units and (4) impact related 

materials. Along with the time sequence of events 

resulting in the emplacement of geologic units, a number of episodes of tectonic activity have acted to shape 

the surface of this part of Venus. The relative sequence of tectonic activity, crustal stretching and extension forming normal faults, fractures and grabens 

along with compression forming sets of wrinkle ridges, 

is identified. 

Lava Flow Materials (fa, fb). Volcanic activity 

within the Juno region has produced a wide variety of 

structures that range from small shields (several to 10s 

of km in diameter), steep sided domes and channels to 

large constructs such as coronae, calderas, and regional-scale, greater than 100-km in diameter, edifices. 

The characteristics of units placed in the category of 

lava flow materials are distinguished by (1) lobate sets 

of deposits whose lengths exceed their width, (2) the 

presence of distinct flow lobes both at the toe and 

along the margins of the flows, (3) a range of backscatter characteristics for different flows, producing a 

local mottled texture. It is generally possible to identify the constructional features that have produced 

these lava deposits, although in most cases specific 

vents cannot be distinguished. 

Tectonic Units (t). Located on the distal flanks of 

the Juno rift, but still associated with the elevated topography of the ridge are three areally extensive elevated outcrops of material identified as tessera. The 

first, made up of two occurrences centered at 27° S, 

100° and 27.5° S, 107.2° respectively corresponds to 

Husbishag Tesserae, and the second, Sudice Tessera, is 

located at 36.4° S, 113.2°. Both parts of Husbishag 

Tesserae and Sudice Tessera rise to an elevation of 

~1.0-km relative to the adjacent plains. 

Plains Forming units (pha, phb, pm, pr, pl). Regional plains forming units make up a majority of the 

quadrangle. These units generally have a homogeneous texture and are interpreted to be extensive lava 

flood deposits. Their emplacement covers a major 

portion of the history of the region. The association of 

the pl unit with outcrops of t suggests that some of the 

tessera forming tectonic events also coincided with 

plains formation. The association of phb with the Juno 

rift and the history of subsequent deformation of this 

unit suggests that its emplacement is related to early 

rift formation. 

Impact Crater Materials (c). Although the density 

of impact craters is not sufficient to provide reliable 

ages for individual map units, impact events have influenced the surface and their associated deposits have 

acted to modify a number of the units. Within the 

Juno quadrangle, sixteen craters that are interpreted to 

be of impact origin are identified. These structures 

range in size from just under three kilometers to over 

73 km in diameter (Boulanger). Mappable crater related materials correspond primarily to the continuous 

ejecta blanket. In addition, extensive surficial deposits 

are identified which include low emissivity parabolas 

(e.g. area of low radar backscatter extending to the 

south and west of Boulanger) and bright and dark halos/annuli. In some places, windblown material is 

identified while in others modification of the surface 

due to the impact blast is observed. 

References. [1] Senske, D. A., et al., LPSC XXV, 

1245-1246, 1994; [2] Senske, D. A., LPSC XXVII, 

1171-1172, 1996; [3] Senske, D. A., Geologic Map of 

the Juno Chasma Quadrangle (V-47), Venus, in prep. 

for submittal to USGS, 2006.
 

Figure 1 Regional-scale geologic map and correlation chart for the Juno Chasma Quadrangle (V-47). Units are 

defined on the basis of patterns in radar backscatter and cross-cutting and on-lapping relations.
GEOLOGY OF THE PHOEBE REGIO QUADRANGLE (V-41), VENUS, D. A. Senske, Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, 91109. 

Introduction. Tessera covers approximately 9% of 

the surface of Venus [1]. The sequence of events and 

the processes involved in the formation of this type of 

landform are currently being examined through the 

geologic mapping of the Tellus Tessera [2] and Phoebe 

Regio Quadrangles. Results from previous analyses 

show that the outcrops of tessera in these areas contain 

distinctly different sets of structural elements [3,4]. 

By evaluating the timing relations between geologic 

units and structural features, a means is provided to 

better determine how these terrains formed. 

Geology of Phoebe Regio. A total of eleven units 

are identified for the Phoebe region (Figure 1). Unit 

definition and characterization is based on an assessment of variations in surface texture, identification of 

coherent patterns of radar backscatter and the presence 

of cross-cutting and on-lapping relations. 

Surface materials mapped as tessera (t) typically 

correspond to the 1.5- to 2.5-km high rise of Phoebe 

Regio and are generally the oldest in the stratigraphic 

sequence. In comparison to Tellus Tessera where the 

tessera fabric is composed primarily of ridges and valleys, that at Phoebe is made up of intersecting horsts 

and grabens, indicating that extension has been the 

dominant form of deformation [3,4]. In several places, 

extensive embayment by regional plains (pr) has produced concentrations of isolated, high-standing outcrops of tessera. This is most readily observed along 

the western part of Phoebe (near 9°S, 280°) and in the 

northeastern part of the quadrangle (near 10°S, 295°). 

Much of the eastern part and southern margin of 

Pheobe has been cross cut by later faulting associated 

with major rift valleys such as the southern extension 

of Devana Chasma (2°S, 289°). These deformation 

belts (db1) are most likely composed of regional plains 

material that has been extensively deformed and modified. Because the high degree of surface alteration has 

resulted in radar properties that are different than other 

regional plains materials, these have been mapped as a 

separate unit. 

A variety of lava flow units are identified. The earliest eruption events are associated with the emplacement of lineated plains (pl). This unit possesses characteristics similar to units mapped in Tellus, but differs 

in that its abundance here is very limited. Subsequent 

to the formation of the lineated plains, volcanic activity associated with the regional plains occurred. More 

recent volcanism has been more localized, forming 

mottled (pm), homogeneous (ph) and shield (ps) plains. 

Source regions for mottled plains are often associated 

with rift related faults, suggesting that extension has 

produced zones along which magma has been allowed 

to migrate to the surface. Units of homogeneous 

plains are typically associated with large volcanic edifices and coronae. Superposition relations indicate 

that this unit is associated with early stage eruptions 

and lava flooding. Later events correspond to the emplacement of digitate plains (pd1) that are typically 

arrayed radial to a summit caldera. Additional occurrences of digitate plains (pd2) correspond to sites of 

early rift related activity. In most cases, the source 

regions for these flows cannot be identified due to later 

faulting and fracturing. 

In a several areas, crater (c) materials including airfall parabolae and halo deposits blanket many of the 

other map units. These relations suggest that impact 

cratering has produced some of the most recent surface 

deposits. 

Volcanic structures located in the Phoebe region include an array of features that range from small shields 

(several to 10’s of km in diameter) to large edifices 

and coronae (> 100 km in diameter). To understand 

better the events in the history of the formation of volcanic features, detailed mapping of two coronae located in the southwest part of the quadrangle (22°S, 

271° and 20.5°S, 273°) has been performed. For both 

features, similar assemblages of units are identified. 

The early history of each corona is characterized by 

the emplacement of laterally extensive homogeneous 

lava flow units that cover 100’s of km2

. The uniform 

texture and lack of identifiable sets of flow lobes 

within the unit suggests that they were most likely emplaced by lava flooding. More recent activity has been 

concentrated along the flanks and summit region of 

each corona. Unlike the more distal homogeneous 

deposits, these are made up of long, digitate systems of 

flows, indicating a change in the style of eruption activity over time. All the volcanic units are cut by systems of faults and fractures, indicating that extension 

has been a late stage process. 

References. [1] Ivanov, M. A. and J. W. Head, 

JGR, 101,14861-14908, 1996. [2] Senske, D. A., 

LPSC XXX, 1999 [3] Hansen, V. L. and J. J. Willis, 

Icarus, 123, 296-312, 1996. [4] Bindschadler, D. L., 

et al., JGR, 97, 13495-13532. 
Figure 1 Regional-scale geologic map and correlation chart for the Phoebe Regio Quadrangle (V-41). Units are 

defined on the basis of patterns in radar backscatter and cross-cutting and on-lapping relations. 
GEOLOGY OF THE TELLUS TESSERA QUADRANGLE (V-10), VENUS, D. A. Senske, Jet Propulsion 

Laboratory/California Institute of Technology, Pasadena, CA 91109. 

Introduction. The processes associated with the 

formation of tessera terrain on Venus are being examined by a number of investigators [1-5]. To understand better the geologic history of individual occurrences of tessera, mapping of the Tellus Tessera Quadrangle (V-10) is being performed. The results from 

this analysis are used to constrain the sequence of 

events in tessera formation along with evaluating the 

relations between tessera and adjacent plains. 

Geology of the Tellus Tessera Region. Based on 

the identification of coherent patterns of radar backscatter along with cross-cutting and on-lapping relations, a total of eight surface material units are identified for the Tellus region (Figure 1). Detailed characterization of these units is based on an assessment of 

variations in surface texture and a quantitative evaluation of their radar properties. 

The tessera (t) material that makes up Tellus is 

generally mapped stratigraphically as the oldest. 

Study of the three dimensional relations along the 

western margin of this upland, however, indicates that 

the adjacent plains often lie on a surface that slopes 

away from Tellus [2, 6], suggesting that post emplacement adjustment has occurred, possibly due to 

isostatic uplift or later tessera formation related activity. A goal of this analysis is to establish the degree to 

which subunits and different deformational episodes 

within the overall context of Tellus can be determined. 

In several locations, the identification of distinct sets 

of structural elements has allowed the mapping of a 

number of domains (tessera units t1 to t4). The central 

part of Tellus, t3, contains an array of intersecting 

ridges and troughs. Outcrops of t3 located along the 

northern boundary are embayed by regional plains, 

producing a number of isolated, high standing “islands” of tessera. Along the northern margin of Tellus 

are eight caldera/corona-like structures that are interpreted to be source regions for some of the surrounding plains material. The subunits t1, t2, and t4 lie 

along the southern and eastern edges of the main outcrop of tessera (t3). Ridges within the t4 subunit appear to reflect tectonic activity associated with adjacent deformation belts (db1). In comparison, compressional deformation associated with the interaction 

between subunits t1, t2, and t3 appears to have resulted 

in the formation of ridges in deformation belt db2. 

Volcanic activity has occurred throughout the Tellus region, being manifested in a variety of plains deposits and edifices. The oldest plains unit, lineated 

plains (pl) is primarily a boundary forming unit with 

Tellus. Additional outcrops are preserved as isolated 

occurrences within the regional plains. In many locations the structure within the lineated plains cross-cuts 

both this unit and adjacent tessera, suggesting that 

some of the events that resulted in the formation of the 

tessera fabric continued after plains emplacement. 

A second episode of plains forming activity is associated with regional plains (pr). These plains embay 

tessera, lineated plains and in some places deformation 

belts (NE-SW trending belts located in the SW part of 

the quadrangle). In most locations, faults and fractures 

within the lineated plains are truncated at the boundary 

with the regional plains, suggesting that the latter are 

younger and that either (1) the rate of tectonic activity 

decreased over time (unlike the lineated plains where 

systems of faults and fractures are pervasive, while 

those in the regional plains are only localized) or (2) 

that the emplacement of the two units was separated by 

a large amount of time, allowing the lineated plains to 

record numerous tectonic events. Superposition relations show that the deformation belts both predate and 

postdate the regional plains, indicating that multiple 

deformation episodes have occurred. 

The youngest units within the Tellus quadrangle 

are local lava flows and crater (c) materials. Based on 

the absence of multiple flow lobes and their uniform 

texture, homogeneous plains (ph ) are interpreted to be 

sites of lava flooding. The remaining two volcanic 

units, digitate plains (pd) and shield plains (ps) are 

associated with volcanic constructs that range from 

several to up to 200 km in diameter. Digitate plains 

are found exclusively in the SW part of the map area 

on the flanks of a 200-km diameter volcano (28°N, 

64°). A nested summit caldera indicates that multiple 

eruption events have occurred. Shield plains, consisting of small volcanic shields and their associated deposits, are found mainly in the eastern part of the 

quadrangle where they are superposed on the regional 

plains. In some locations, individual shields are both 

superposed and cross cut by background structure, 

indicating that within each field, volcanic activity has 

covered a range of time. Crater materials correspond 

to impact structures and their associated ejecta. Extensive, up to 1000’s of km2

, halo deposits generally blanket most units, indicating that impact craters are often 

some of the most recent features. 

References. [1] Binschadler, D. L. and J. W. Head, JGR, 

96, 5889-5907, 1991. [2] Ivanov, M. A. and J. W. Head, 

JGR, 101, 14861-14908, 1996. [3] Hansen V. L. and J. J. 

Willis, Icarus, 123, 296-312, 1996. [4] Hansen V. L. and J. 

J. Willis, Icarus, 132, 321-343, 1998. [5] Gilmore, M. S., et 

al., JGR, 103, 16813-16840, 1998. [6] Senske, D. A., LPSC 

XXIX, 1745-1746, 1997. 
Figure 1. Regional-scale geologic map and correlation chart of the Tellus Tessera Quadrangle (V-10). Units are 

defined on the basis of patterns in radar backscatter and cross-cutting and on-lapping relations. Although tessera is 

identified as the oldest unit, an upper bound on the timing of activity in its formation is not clearly defined. Recent 

activity associated with the formation of plains and flow units is focused at sites of digitate plains, shield plains and 

homogeneous plains.
MAPPING OF QUADRANGLE V-53: THEMIS REGIO. E. R. Stofan1,2 and A. W. Brian2

1

Proxemy Research, 20528 Farcroft Lane, Laytonsville, MD 20882, (ellen@proxemy.com), 

2

Department of Earth Sciences, University College London, WC1E 6BT UK. 

 Introduction: A geologic map of the 

Themis Regio (V-53) quadrangle has been 

completed at 1:5,000,000 scale as part of the 

NASA Planetary Geologic Mapping Program. 

The quadrangle covers a portion of the Parga 

Chasmata system, and has extensive rifting, 

numerous coronae, and abundant volcanism. 

We mapped this region to better define the 

relationship between corona formation and 

rifting, to study the relationship between rifting and volcanism, including coronae, and to 

determine the stratigraphic relationship of 

plains-forming units [e.g., 1, 2]. 

Quadrangle Overview: The Themis Regio Quadrangle (V-53) extends from 25° - 

50° S. latitude, 270° - 300° E. longitude, and 

includes the Themis Regio highland, surrounding plains, and the southernmost portion 

of Parga Chasmata. V-53 consists of lowlying plains lying slightly below Mean Planetary Radius (MPR, 6051.84, [3]). The topographically lowest points in the quadrangle 

(about 2 km below MPR) are within the 

Parga rift and in the troughs around several 

coronae. 

We have identified seven plains materials 

units within the V-53 quadrangle: uniform 

plains materials (unit pu), smooth plains materials (unit ps), mottled plains material (unit 

pm), Themis Regio lobate plains material 

(unit pTl), Themis Regio fractured plains material (unit pTf), Helen Planitia composite 

plains (unit pHc) and densely fractured plains 

material (unit pdf). None of the plains units 

within this quadrangle are analogous to regional-scale plains units mapped in other 

quadrangles, such as the Aino composite 

plains in quadrangle V-46 [4]. This is largely 

due to the fact that much of the region has 

been resurfaced by flows associated with 

coronae and volcanoes. The Themis Regio 

lobate plains unit is mapped on the Themis 

Regio volcanic rise (Figure 1), and is characterized by flows from an unknown source. 

These units are likely to not be of the same 

age; some may be volcanic flows that have 

originated from rift fractures, while others 

have come from unknown edifices or coronae. The Themis Regio fractured plains unit 

is composed of multiple occurrences of heavily fractured plains on the Themis volcanic 

rise. They may represent plains units off the 

rise that were elevated and deformed (such as 

unit pu or unit ps), or they may represent earlier corona or volcano flows that have been 

subsequently deformed. 

Figure 1. West-central portion of the Themis Regio quadrangle, showing corona flows (unit fSe, unit 

fTy) overlapping onto plains units, including the 

Themis lobate plains (unit pTl) and the uniform plains 

(unit pu). 

Eleven units associated with specific 

named volcanic edifices have been mapped, 

including those associated with the large volcanoes Chloris Mons (Figure 2), Mielikki 

Mons and Tefnut Mons. Multiple materials 
units associated with unnamed or unknown 

sources have also been mapped and combined 

into a single unit. These include a volcanic 

center unit (unit vc), and edifice field unit 

(unit ef) and an unnamed volcano unit (unit 

fvu). Although these units have similar morphologies, the different occurrences have differing relationships with surrounding units, 

indicating that they did not form at the same 

time. Most of the volcanic flow units are not 

in contact with each other, or with consistent 

plains or corona units, making an overall volcanic stratigraphy difficult to determine. 

Figure 2. Chloris Mons (45°S, 294°E; 400 km). 

Eighteen named coronae have mapped 

flow materials units in the V-53 quadrangle, 

along with units associated with two unnamed coronae. Some of the coronae have 

multiple associated flow units, including 

Ukemochi Corona, with five associated units, 

and Tamiyo Corona, with four associated 

flow materials units. Where coronae have 

multiple units, the flow units are interfingered 

with units from adjacent coronae, suggesting 

that corona formation overlapped over some 

likely significant period of time. Coronae 

with abundant associated flows are located 

both on and off the rift, and on and off the 

volcanic rise. Recent work by Martin et al. 

[2] indicates that coronae on the Themis volcanic rise have more associated volcanism 

than other coronae in the Parga region. 

There are 12 impact craters within the 

quadrangle. Most postdate the units upon 

which they lie, but subtle embayment relationships with surrounding units are possible. 

Some age relationships can be determined 

between some of the coronae and volcanic 

edifices, with no clear pattern observed. 

Some coronae predate rifting, some postdate 

it, while most are interpreted to have formed 

largely synchronously with rifting. 

Conclusions: Unlike many other Venus 

quadrangles, V-53 lacks regional-scale plains 

units. In V-53, the scale of plains units tends 

to be on the order of 100’s of kms rather than 

1000’s of kms and much of the region has 

been resurfaced from flows from volcanoes 

and coronae. We have chosen to lump plains 

units of relatively similar morphology into 

units (examples: unit pTl, unit pm) that are 

unlikely to have originated from the same 

source or have formed at the same time. 

Along Parga Chasmata, coronae are located along the rift, as well as to the north 

and the south of the rift [2], similar to the 

situation along Hecate Chasma [5]. Coronae 

in this quadrangle exhibit all forms of corona 

topographic shapes, including depressions, 

rimmed depressions, plateaus and domes. 

Most of the coronae formed synchronously 

with the rifting, although some clearly predate the rifts and others postdate extensional 

deformation [2]. 

A strong association between volcanism 

and coronae along rifts has been noted elsewhere on the planet [6]. In V-28 [5] and V53, some coronae along the rift do not have 

much associated volcanism; coronae with the 

most associated volcanism in these quadrangles are located at least 500 km off the rifts or 

on the Themis Regio highland. While extension clearly plays a role in volcanism at coronae [6], it is not the only contributing factor. 

Coronae at Themis Regio may have greater 
than average associated volcanism owing to 

the possible mantle plume beneath the rise. 

 The large number of plains units, 

coronae and volcanoes in this quadrangle results in a very horizontal stratigraphic column, as few units are in direct contact. The 

scale of resurfacing in this quadrangle is on 

the scale of 100’s of kilometers, consistent 

with the fact that it lies in the most volcanic 

region of Venus. 

Map Timeline. The map of V-53 has been 

completed and a copy has been sent along 

with this abstract. The text, DOMU and 

stratigraphic column are being finalized, and 

the map will be submitted by mid- July, 2006. 

 References: [1] Stofan, E.R. and S.E. Smrekar, 

Proceedings of Mantle Plume IV Penrose Conf., GSA

Special Paper 388, 841-861, 2005. [2] Martin, P., E. 

Stofan, L. Glaze and S.E. Smrekar, in review, JGR, 

2006. [3] Ford, P. G., and Pettengill, G. H. (1992) JGR, 

v. 97, 3,103-13,114. [4] Stofan, E.R. and J.E. Guest, 

Geologic Map of the Aino Planitia Quadrangle (V-46), 

Venus, USGS Geologic Investigations Series Map I2779, 2003. [5] Stofan, E.R., J.E. Guest and A.W. 

Brian, Geologic Map of the V-28 Hecate Chasma Quadrangle, in review, U.S. Geological Survey, 2005. 

[6] Magee, K.P. and J.W. Head (1995) JGR 100, 1527-

1552. 
GLOBAL GEOLOGIC MAP OF EUROPA. T. Doggett1

, P. Figueredo1,*, R. Greeley1, T. Hare2, E. Kolb1, K. Mullins2, D. Senske3, K. Tanaka2, 

S. Weiser1

, 1Department of Geological Sciences, Arizona State University (tcd@asu.edu), 2U.S. Geological Survey, Flagstaff, AZ, 3Jet Propulsion 

Laboratory, California Institute of Technology, Pasadena, CA., (*currently at the ExxonMobil Research Company, Houston, TX).

Introduction: Europa, with its indications of a sub-ice ocean, is 

of keen interest to astrobiology and planetary geology. Knowledge 

of the global distribution and timing of Europan geologic units is a 

key step for the synthesis of data from the Galileo mission, and for 

the planning of future missions to the satellite.

The first geologic map of Europa [1] was produced at a hemispheric scale with low resolution Voyager data. Following the acquisition of higher resolution data by the Galileo mission, researchers have identified surface units and determined sequences of events 

in relatively small areas of Europa through geologic mapping [2-6] 

of images at various resolutions acquired by Galileo’s Solid State 

Imaging (SSI) camera [7]. These works [2-6] provided a local to 

sub-regional perspective and employed different criteria for the 

determination and naming of units. Unified guidelines for the identification, mapping and naming of Europan geologic units were put 

forth by [8] and employed in regional-to-hemispheric scale mapping 

[9,10] which is now being expanded into a global geologic map. 

Methodology: A global photomosaic [11] of Galileo and Voyager data was used as a basemap for mapping in ArcGIS, following 

suggested methodology of allo-stratigraphy for planetary mapping 

[12]. Due caution was exercised given that the mosaic has a resolution varying from 12.6 to 0.23 km per pixel, as well as variations in 

illumination and viewing geometry, to avoid making distinctions 

between units that are artifacts of these variations. 

Geologic History:

Background Plains Material (unit p1). This unit forms globally 

extensive plains that appear smooth at regional or global resolution 

(Figure 1), but are intensely ridged at higher resolution. It is characterized by cross-cutting ridges and troughs at multiple scales, with 

various geometries including arcuate, sinuous and anastomosing. It is 

disrupted in some localities by pits and domes and is sparsely cratered. It is older than all other units, acting as a background for all 

other stratigraphic units and structures and is equivalent to the ridged 

plains material (unit pr) defined in [8]. 

Figure 1: Unit p1 in the northern hemisphere, at 1.57 km/pixel. 

Unit p1 is interpreted to represent tectonic resurfacing of Europa 

during a period of more intense and denser lineament formation. As 

indicated by the relative lack of cratering, this occurred relatively 

recently compared to the age of the solar system. 

Initial mapping separated unit p1 into two units, with a more 

knobby or mottled plains in portions of the polar regions that also 

had an apparent difference in the cross-cutting lineaments being both 

wider in size and spacing. However, except for an albedo contrast in 

some low-resolution (12.6 km/pixel) data, only a gradational contact 

could be drawn, which provided no definitive evidence of their relative ages, although intuitively the more lenticulated plains might 

seem to be younger. This distinction was discarded as too tenuous 

for a consensus geologic map, and may be attributed to regional 

differences in the degree of lenticulation, and possibly thermal inertia (Spencer, pers. comm.), within the same unit. 

 Argadnel Regio Unit (p2). In Argadnel Regio the background 

plains unit is disrupted by wide cycloid lineaments to a degree that 

warrants a definition as a separate, younger plains unit (Figure 2). 

This is interpreted to be tectonic disruption, probably by tidal stress 

forces, of the older plains unit. It is partially equivalent to the dark 

plains unit in Voyager mapping [1].

Figure 2: p2 unit in Argadnel Regio, at 0.23 km/pixel. 

Antipodal Dark Plains Material (unit p3). This unit forms equatorial plains, in two occurrences, centered on the sub-Jovian and antiJovian points respectively, which are darker than surrounding plains. 

It has a speckling of domes and sharp contacts with surrounding 

brighter plains, giving the overall resemblance of a scab on skin. 

The unit contains occasional impact craters, like Cilix, which are 

readily apparent because of the contrast between bright ejecta and 

dark plains. It embays surrounding plains (p1, p2) units, but is crosscut by numerous lineaments continuing on from adjacent units. In 

some cases the boundaries of unit p3 conform to the ridges or abut 

against cycloids from unit p2. 

Unit p3 is interpreted as the modification of pre-existing plains 

unit by some form of endogenic activity, which floods inter-ridge 

topographic lows with dark, viscous material that erupted from lenticulae within the unit, and is thus somewhat of an intermediate 

between ridged plains and chaos. The geographic association with 

the sub-Jovian and anti-Jovian points is intriguing, suggesting the 

possibility of the global stress field controlling the occurrence of this 

unit, or the particle field environment having an effect on the coloring of the unit, but it could also be coincidental. The occurrence of 

this unit centered on the 180 longitude line is equivalent to the gray 

mottled terrain unit in the Voyager map [1].

Lineaments. Distinct from the densely spaced ridges in the 

background plains are the widely spaced lineaments that consistently 

cross-cut younger plains units (p1, p2 and p3). These lineaments 

appear to represent a middle period of the geologic time represented 

by Europa’s current surface, with some lineaments being overprinted 
EUROPA GLOBAL MAP: T. Doggett et al. 

by younger chaos and plains units, and all but two craters (the exceptions being Tyre and Callanish, which have some superimposed 

lineaments).

A manuscript in preparation for submission to Icarus [13] details the global mapping and sequencing of all major lineaments 

(>100 km in length) into seven sparsely connected regional networks 

that are broken up by intervening areas of chaos and/or low image 

resolution. These networks define regional stratigraphic frameworks 

that allow temporal correlation of features on a hemispheric scale. 

Disrupted Plains Material (unit p4). This unit forms a hummocky terrain which is cross-cut by narrow lineaments, mostly 

troughs. The craters Avagddu, Tegid and Morvran are superimposed 

on this unit, forming distinct raised circular rims, and in the case of 

Tegid, a trough-like annulus. It has a sharp contact with surrounding 

plains units (p1 and p3), which it embays, and a sharp contact with 

the chaos unit that in turn embays it. Triple bands coming from 

surrounding plains become obscured within the unit, transitioning to 

narrow troughs or fading altogether. 

This unit is interpreted to be the result of endogenic activity that 

severely disrupted the pre-existing plains unit, fragmenting it into 

hummocks and massifs, a transitional form between plains and 

chaos. The surface expression of lineaments was altered into negative relief, or obscured altogether. 

Lenticulated Plains Material (unit pl). This unit forms regions 

where a plains unit (p1 or p2) acts as a matrix upon which lenticulae 

have been emplaced. No craters are observed within the lenticulated 

plains, which is consistent with a young age, or simply too little areal 

coverage. It is either younger or contemporaneous with p3, p4 and 

chaos units. It is cross-cut by most, but not all, lineaments. 

It is interpreted to be the result of endogenic activity that disrupted pre-existing plains, in a manner possibly analogous to a volcanic field, where the lenticulae have not yet reached sufficient density to form a knobby chaos unit, and the plains unit has not been 

disrupted enough to fragment or become discontinuous. They can 

either be younger or contemporary to more continuous chaos units, 

and were called micro-chaos in some regional mapping [3]. 

Chaos Material (unit ch). This unit is composed of disrupted 

terrain which forms dark albedo features in global or regional resolution, having sharp embaying contacts with brighter, smoother plains 

units (Figure 3). In low resolution this unit can also have transitional 

areas of dark albedo spots in a light albedo matrix, but this could also 

be equivalent to what has been mapped as lenticulated plains in high 

resolution (Figure 4). At higher resolution the chaos is seen to be 

hummocky plains, with plates of younger plains units in a matrix of 

dark, knobby material. There are several separated occurrences 

globally, with different appearances, but nothing that could not be 

explained by differences in photometry and resolution within the 

base mosaic. Chaos is younger than all surrounding material units, 

with some cross-cutting lineaments. A sub-type is elevated or 

knobby chaos that is younger than other chaos units [9, 10]. They 

are interpreted to be located where pre-existing plains units have 

been disrupted by an endogenic process that fractures the ice into 

plates and rafts them in a matrix of material brought to the surface 

from the interior, overturned plates, or both. 

 Figure 3: Conamara Chaos, type locality for chaos unit [8] 

Figure 4: Example of apparent textural difference in chaos unit 

across resolution boundary. 

References: [1] Lucchitta and Soderblom, in The Satellites of Jupiter: 521, 1982. [2] Senske et al., LPSC XXIX, #1743, 1998. [3] 

Prockter et al., JGR., 104, 16531-16540, 1999. [4] Kadel et al., JGR, 

105, 22657-22669, 2000. [5] Figueredo et al., JGR, 107, 

10.1029/2001JE001591, 2002. [6] Kattenhorn, Icarus, 157, 490-506, 

2002. [7] Belton et al., Space Science Reviews, 60, 413-455, 1992. 

[8] Greeley et al., JGR, 105, 22559, 2000. [9] Figueredo and 

Greeley, JGR, 22629-22646, 2000. [10] Figueredo and Greeley, 

Icarus, 167, 287-312, 2004. [11] USGS, I-2757, 2003. [12] Skinner 

and Tanaka, LPSC XXXIV, #2100, 2003. [13] Figueredo, Weiser and 

Hare, Icarus, in prep., 2006. 
A GLOBAL GEOLOGIC MAP OF GANYMEDE AT 1:15M. G. Wesley Patterson1

, James W. Head1, Geoffrey

C. Collins 2, Robert T. Pappalardo3, Louise M. Prockter4, and Baerbel K. Lucchitta5, 1Department of Geological Sciences, Brown University, Providence, RI, 02912 (Gerald_Patterson@brown.edu), 2

Wheaton College, Norton, MA,

02766, 3LASP, University of Colorado, Boulder, CO, 80309, 4Applied Physics Laboratory, Laurel, MD, 20723, 5

USGS, Flagstaff, AZ, 86001.

Introduction: The Galilean satellites represent a series of bodies that all formed from the same protoJovian nebula but are distinctly different in their physical properties, surface geology, and thermal evolution

[1-4]. The explanation for many of these disparate

characteristics is likely related to the radially varying

conditions of the nebula during the earliest period of

their formation [5-6]. However, an explanation for the

differences in the geological evolution of Ganymede

and Callisto, given their similar size, density, and bulk

composition, remains one of the most fundamental

questions in comparative planetology [6, 7]. Understanding the global distribution of geologic units on

Ganymede in space and time can offer constraints on

our ideas of how and why this icy satellite evolved to

its present state.

The Voyager mission provided important information about the nature of the surface of Ganymede at

moderate resolution and these data were used to produce a series of geologic maps covering the imaged

surface at the 1:5M scale [e.g., 8-10]. The Galileo mission provided a host of new data (high-resolution

monochromatic, color, and stereo imagery, polarimetry,

near-infrared spectral imagery, etc.) and we are compiling a global geologic map of Ganymede (at the

1:15M scale) that will represent the most recent understanding of the satellite on the basis of this data. This

contribution builds on important previous accomplishments in the study of Ganymede [11-15] and here we

summarize our progress toward the completion of this

global mapping project.

Unit definitions: Based on a reassessment of the

units identified at Voyager resolution using Galileo

resolution data [16, 17], we have developed a Description of Map Units (DOMU) that divides the surface of

Ganymede into five terrain types: 1) light, 2) dark, 3)

reticulate, 4) palimpsest, and 5) crater material. The

following is a summary of those definitions.

Light material: This material has been subdivided

into four units: grooved, subdued, irregular, and undivided. The grooved unit (lg) is arranged in domains

characterized by parallel, approximately evenly spaced

grooves and ridges oriented in a single dominant direction. The subdued unit (ls) is similar to the grooved

unit but appears smooth or finely grooved at Galileo

and/or Voyager resolution except where secondary

craters and crater chains are superposed. The irregular

unit (li) is similar to the subdued unit but contains isolated grooves with no preferred orientation. The undivided unit (l) represents all materials of sufficiently low

resolution for which morphological properties and/or

age relationships cannot be determined.

Dark material: This material has been subdivided

into four units: cratered, lineated, irregular, and undivided. The cratered unit (dc) represents large areas of

low albedo material with moderate to high crater density commonly occurring as polygons bounded by

bright units. The lineated unit(dl) is similar in character to the bright grooved unit but with lower albedo and

depressions tending to be more sinuous and shallower.

The dark irregular unit (di) is characterized by isolated

grooves with no preferred orientation similar to the

light irregular unit but having an albedo characteristic

of dark materials. The undivided unit (d) represents all

materials of sufficiently low resolution that their material properties cannot be determined. This also may

include irregularly shaped large patches and small slivers of low albedo material interspersed within light terrain of indistinct morphology or areas too small to be

identified by morphologic criteria other than albedo.

Reticulate material (r): This terrain consists of a

single unit. It is often associated with and surrounded

by bright grooved, bright subdued, and/or dark lineated

units but can be distinguished from them by its variable

albedo and presence of grooves with two dominant directions (typically orthogonal to each other).

Palimpsest material: This material consists of two

units: palimpsests and palimpsest interior plains. The

palimpsest unit (p) is characterized by flat, generally

circular to elliptical structures occurring predominately

(but not exclusively) on dark terrain units. These

structures lack rims but can have internal, concentric

ridges. The palimpsest interior plains unit (pi) is characterized by smooth, circular to subcircular patches of

high albedo material commonly found at or near the

center of palimpsests.

Crater material: This terrain consists of seven

units: bright craters, partly degraded craters, degraded

craters, secondary craters, dark crater material, basin

rugged material, and basin smooth material. The first

three units separate craters into a stratigraphic sequence

(c1, c 2, and c3 from oldest to youngest respectively)

based on degradation state, which we feel can be more

clearly determined than for palimpsests. The secondary

crater unit (cs) is characterized by fields of uniform,

small pits surrounding large bright craters, partly degraded craters, and some palimpsests. Dark crater

material (cd) appears to be predominately associated

with bright craters and forms dark patches on their

floors or rims. The basin rugged material (br) and

basin smooth material (bs) units are used to define the

prominent Gilgamesh basin.

Mapping strategy: Using the DOMU presented

here, we are completing the compilation of a global

geologic map of the surface of Ganymede. In accom-
A GLOBAL GEOLOGIC MAPPING OF GANYMEDE AT 1:15M. G. W. Patterson et al.

plishing this task we have 1) broadly mapped the

boundaries of terrain types (i.e., dark and light materials, craters, palimpsests, reticulate) and superimposed

structures (i.e. furrows) across the surface of Ganymede

and 2) compiled detailed maps of geologic units (e.g.,

light grooved, dark cratered, palimpsest interior plains,

etc.) in 60 ̊x 60 ̊ quadrangles. The assigned unit

boundaries have been reviewed and modified as necessary within each quadrangle before proceeding to the

next. The minimum dimension we have established for

mapping a feature as a unit is 30 km (2 mm on the

map). This map (Fig. 1) is being produced entirely in

GIS format for analysis and combination with other

datasets.

Status: We have completed the detailed mapping

of light materials, dark materials, reticulate materials,

palimpsests, and furrows for the entire surface of Ganymede (Fig. 1). We have also broadly mapped all

craters >30 km. Our remaining tasks are to map the

extent of the Gilgamesh basin and finalize the remaining issues in the stratigraphic sequence for the material

units we have mapped. Specifically, for light materials,

we will be relying on an automated time-sequencesorting of grooves technique we have developed [18]

and, for crater materials, we will be relying on the presence of bright rays to separate craters into two units.

References: [1] R. Greeley (1999) The New Solar System,

253-262. [2] R.T. Pappalardo (1999) The New Solar System,

263-276. [3] W.B. McKinnon and E.M. Parmentier (1986)

Satellites, 718-763. [4] G. Schubert et al. (1986) Satellites,

224-292. [5] D.J. Stevenson et al. (1986) Satellites, 39-88 [6]

T.V. Johnson (2004) Physics Today, 57, 77-83. [7] D.J. Stevenson (2004) Physics Today, 57, 43-48. [8] J.E. Guest et al.

(1988) USGS Map I-1934. [9] D.E. Wilhelms (1997) USGS

Map I-2242. [10] B.K. Lucchitta et al. (1992) USGS Map I2289. [11] B.K. Lucchitta (1980) Icarus, 44, 481-501. [12] E.

M. Shoemaker et al. (1982) Sats. of Jupiter, 435. [13] S. Murchie et al. (1986) JGR, 91, E222-E238. [14] R.T. Pappalardo

et al. (1998) Icarus, 135, 276-302. [15] L.M. Prockter et al.

(1998) Icarus, 135, 317. [16] G.C. Collins et al. (2003) PGG

Planetary Mappers Meeting. [17] G.W. Patterson et al. (2003)

PGG Planetary Mappers Meeting [18] E.S. Martin et al.

(2006) LPSC #1204.

Figure 1. Global geologic map of Ganymede compiled utilizing the DOMU presented here.
GLOBAL GEOLOGIC MAPPING OF IO: FIRST STEPS. David A. Williams, Department of Geological Sciences, Arizona State University, Box 871404, Tempe, Arizona, 85287 (David.Williams@asu.edu); Laszlo Keszthelyi, Paul Geissler, Windy Jaeger, and Tammy Becker, Astrogeology Team, U.S. Geological Survey, Flagstaff, Arizona; David Crown, Planetary Science Institute, Tucson, Arizona. 

Introduction: The objective of this work is to discuss mapping methodology for producing a new global 

geologic map of Io using the new global Io mosaics. 

These mosaics, produced by the USGS at a nominal 

resolution of 1 km/pixel, combine the best images 

from the Galileo and Voyager missions. To develop a 

mapping methodology we have studied the preliminary 

mosaics, all previous Voyager- and Galileo-based geologic maps of Io, and new maps of the Amirani-Gish 

Bar region that we recently produced from a ~500 

m/pxl regional mosaic. In this abstract we present an 

overview of the classes of geologic material units and 

structures that can be identified from existing images, 

and we discuss our conclusions about the best mapping 

approach to produce a new global map of Io.

Background: Io, the innermost Galilean satellite of 

Jupiter, is the most volcanically active body in the Solar System. Tidal heating within Io produces magma 

that feeds ~300 active volcanic centers [1-3]. The 1979 

Voyager flybys observed ~25% of the moon at resolutions of <2 km/pixel (the rest at 2-20 km/pixel: [4]), 

covering mostly the subjovian hemisphere. The recently completed Galileo mission (1996-2003) included five close flybys of Io, focused mostly on the 

antijovian hemisphere [5-7], with resolutions between 

~10 m/pixel to 20 km/pixel. This complementary coverage of Io has enabled the production of a series of 

high quality grayscale (high-sun and low-sun) and 

color global mosaics (1 km/pixel nominal resolution). 

These recently-completed mosaics, produced by the 

USGS, are now the definitive global compilation of 

image products for Io. 

Our goal is to complement the new mosaics with a 

corresponding global compilation of geologic understanding at the end of the Galileo era. Geologic mapping is a tool that enables the definition and characterization of surface features into process-related material 

units and structures and places them within their stratigraphic context, allowing recognition of the geologic 

evolution of an area, region, or planet (depending upon 

the scale of the mapping). Before global mapping begins on the new Io mosaics, it is prudent to identify the 

optimal mapping methodology. Such an activity was 

done prior to global mapping of Europa [8].

Overview of Ionian Materials & Structures: Io 

displays five primary types of material units: plains, 

patera floors, flows, mountains, and diffuse deposits. 

Plains cover >70% of Io’s surface [9], and appear as 

yellow (S-dominated), gray-white (SO2-dominated), 

and red to red-brown (radiation-altered, short-chain 

sulfur-dominated) color units in Galileo images. Plains 

are thought to consist of the silicate crust of Io, mantled by dark silicate and bright sulfurous volcanic deposits [10-11]. Eroded plateaus, or layered plains, have 

also been detected in low-sun images and are mappable at global scales. 

Patera floors have a range of albedos and colors, 

and these materials sometimes extend outside these 

volcano-tectonic depressions. Patera floors range from 

bright white to yellow-orange to dark black in Galileo

images, in which the colors suggest various compositions, including mixes of silicates, sulfurous compounds, and relatively pure sulfur dioxide in some 

cases [3, 11]. Three broad subunits of patera floor materials are characterized for mapping: Bright (presumably sulfur-dominated), Dark (presumably silicatedominated), and Undivided. 

Lava flow units are also characterized by their albedo and color: Bright flows (sulfur-dominated), Dark 

flows (silicate-dominated), and Undivided Flows 

(units with intermediate albedos and colors). Two subunits are used for both bright and dark flows based on 

their inferred “freshness”; i.e., the youngest bright 

flows are very bright (high albedo), the youngest dark 

flows are very dark (low albedo). Flow materials are 

typified by their sharp contacts with the other units and 

generally elongated morphology (lengths >> widths: 

[10-12]). Correlation between Galileo Near Infrared 

Mapping Spectrometer and Solid State Imager data 

also shows that the darkest flow materials are associated with active hot spots [3, 13]. Lithologically, 

patera floor materials and lava flow units are probably 

identical. However, their distinctive geologic settings 

justifies separating them in the global map. 

We recognize three types of mountain materials in 

regional images: Lineated, Mottled [12], and Undivided [13], although for the global mapping we map 

only massifs and layered plains. Lineated materials are 

associated with topographically-distinct ridges, 

grooves, graben, scarps, and lineaments on positiverelief edifices. This unit is interpreted as tectonicallydisrupted sections of crust containing planar structural 

features, possibly faults involved in uplift and/or collapse during mountain formation. Mottled materials 

contain lobes or domical mounds that are lacking in 

lineations. This unit is interpreted as sections of mountains that show evidence of mass wasting processes, 

most likely involving flow with or without rotational 
GEOLOGIC MAPPING OF IO: D.A. Williams et al. 

sliding [2, 12, 16]. Mountain material whose morphology does not fall within either of these two units is 

classified as Undivided. Volcanic mountains on Io are 

rare; the few edifices that have been found are mapped 

as Tholus materials. 

Diffuse deposits are diverse on Io’s surface, which 

was recognized because of the higher resolution color 

imaging of the Galileo camera. White Diffuse deposits 

are thought to be dominated by SO2-rich frosts. Yellow Diffuse deposits are likely composed of some 

combination of sulfur-rich materials and SO2, albeit 

less SO2, than white deposits. Red Diffuse deposits 

occur as ephemeral mantles around active vents. They 

have been interpreted as pyroclastic deposits rich in 

metastable, S3 and S4 allotropes, which are red when 

quenched from magmatic S2 gas [6, 14], possibly also 

containing Cl-bearing materials at some vents [15]. 

Dark Diffuse deposits are interpreted as pyroclastic 

deposits derived from silicate lavas; Geissler et al. [9] 

performed a spectral analysis on the dark diffuse deposits from Babbar and Pillan Paterae, and found a 

spectral signature consistent with Mg-rich silicates. 

Finally, Green Diffuse deposits occur around active 

vents and underneath or near active plumes, where 

dark, fresh silicate flows also underlie the green material. This observation led to the suggestion that the 

green color results from alteration of cold sulfurous 

gases interacting with still warm silicate flows.

A wide range of structural features can be identified on Io, including scarps, ridges, graben, lineaments, faults, and circular depressions (pits and patera 

rims). The additional low-sun observations and higher 

resolution of the Galileo camera has enabled recognition of these and other structural features over a wider 

part of Io’s surface than was previously possible.

Strategies for Global Mapping: After analysis of 

our new regional maps of the Amirani-Gish Bar region, analysis of previous geologic maps, and study of 

early versions of the new global Io mosaics, we have 

developed the following strategy for global mapping 

on the new mosaics with ArcGIS by ESRI. 

1) Map diffuse deposits using Galileo global color 

data: The first mapping step will be to map diffuse 

deposits as a separate layer using the color mosaics. 

Typically various hachure patterns are used to delineate different types of diffuse deposits, and this approach will be used here. The wide variety of diffuse 

deposits on Io (black, yellow, white, red, green), which 

are thought to represent distinct compositions (silicates, sulfurous materials, SO2-dominated materials, 

short-chain sulfur allotropes, products of silicate/sulfur 

interaction, respectively), cannot always be discerned 

in grayscale images. The color images are required to 

map their diversity. Based on analysis of the preliminary global color mosaic, all five types of diffuse deposits are resolvable (1 km/pixel) and mappable. 

2) Map mountains, surrounding plateaus, and 

structural features using the low-sun mosaic: The second mapping step will be to map mountains, layered 

plateaus, and other materials delineated by scarps and 

other structural features using the low-sun mosaic. 

Because mountains and plateaus have nearly the same 

color and texture as background plains, it is difficult to 

reliably identify them except from images taken during 

low solar incidence angles, resulting in shadows that 

delineate the rugged topography of ridges, grooves, 

and scarps. We anticipate having one unit, Mountain 

Material, for the global (paper) map, with the potential 

of defining additional subunits (e.g., Lineated vs. Mottled, massifs, mesa/plateaus, volcanic edifices) depending on their resolvability in the final mosaics. One option might be to create a separate structural map showing identified and inferred structural features (e.g., 

thrust faults). 

3) Map vents and paterae: The third mapping step 

will be to map vents and paterae using the grayscale 

and high-sun color mosaics. These image products 

provide the greatest albedo and color (respectively) 

contrasts available to identify these features. Active 

vents are usually visible as dark spots in the bright 

plains or within the floors of larger paterae. We anticipate having one unit, Patera Floor Material, for the 

global (paper) map, with the potential of defining additional subunits (e.g., bright, dark, undivided and/or 

intermediate) depending on their detectability and 

scale in the final mosaics. 

4) Map lava flow fields: The fourth mapping step 

will be to map flow fields using the grayscale and 

high-sun color mosaics. We will first map the outermost boundaries of each flow field around a vent, followed by the addition of more detail (lobate flow margins or fresher interior flows) as the available resolution permits. Active or recently active flows are identified by the following criteria: 1) observed surface 

changes in images obtained at different times; 2) thermal anomalies detected in NIMS data; and/or 3) an 

observed plume source at or near the flow margins. 

Based on analysis of the preliminary global color mosaic, we anticipate having three primary Lava Flow 

Material units (bright, dark, undivided) that are resolvable (1 km/pixel) and mappable. 

5) Map plains: The final mapping step will be to 

map the bright plains. This should include everything 

not mapped in the previous categories. The primary 

Interpatera Plains Material has three subunits based on 

color (Yellow, White, and Red-Brown), as well as a 

Layered Plains unit composed of plateaus separated 

from surrounding plains by scarps and thought to be 

produced by degradational processes [16]. 

References: [1] Radebaugh et al., 2001, JGR 106, 33,005-

33,020; [2] Schenk et al., 2001, JGR 106, 33,201-33,222; [3] Lopes 

et al., 2004, Icarus 169/1, 140-174; [4] Smith et al., 1979a,b, Science

204, 951-972, & Science 206, 927-950; [5] McEwen et al., 2000, 

Science 288, 1193-1198; [6] Keszthelyi et al., 2001, JGR 106, 

33,025-33,052; [7] Turtle et al., 2004, Icarus, 169/1, 3-28; [8] 
Greeley et al., 2000, JGR 105, 22,559-22,578; [9] Geissler et al., 

1999, Icarus 140, 265-282; [10] Williams et al., 2002, JGR 107, 

5068, doi:10.1029/2001JE001821; [11] Williams et al., 2004, Icarus, 

169/1, 80-97; [12] Williams et al., 2005, Icarus, 177, 69-88; [13] 

Lopes et al., 2001, JGR 106, 33,053-33,078; [14] Spencer et al., 

2000, Science 288, 1208-1210; [15] Schmidt and Rodriguez, 2003, 

JGR 108, 5104, doi: 10.1029/2002JE001988; [16] Moore et al., 

2001, JGR 106(E12), 33,223-33,240.
THE LUNAR GEOLOGIC MAPPING PROGRAM: SUMMER 2006 STATUS. L.R. Gaddis1

, J.A. 

Skinner, Jr.1

, T. Hare1, K. Tanaka1, B.R. Hawke2, P. Spudis3, B. Bussey3, C. Pieters4, and D. Lawrence5, 1

U.S. Geological Survey, Astrogeology Program, 2255 N. Gemini Drive, Flagstaff, AZ 

(lgaddis@usgs.gov), 2

PGD/SOEST, Univ. Hawaii, Honolulu, HI; 3Johns Hopkins Univ., Baltimore, MD; 4

Dept. Geological Sciences, Brown Univ., Providence, RI; 5Los Alamos National Laboratory, Los Alamos, NM. 

Introduction: A pilot lunar geologic mapping 

program is underway [1-3] with funding from the 

NASA Planetary Geology and Geophysics (PGG) 

Program. As part of this project, we are mapping a 

quadrangle at 1:2.5 M scale centered on Copernicus 

crater [4-8]. A major science emphasis of this 

work is the characterization of crater rays and their 

implications for the identification of the Copernican/Eratosthenian boundary [9, 10]. The goals of 

this pilot are to (1) demonstrate integrated use of 

digital remote sensing data for lunar geologic unit 

mapping and (2) develop a renewed systematic 

mapping program for the Moon as a core element 

of lunar science investigations. Scientists interested in participating in this program should propose a topical lunar science investigation, with a 

geologic mapping component, to the PGG Program. 

Lunar Geologic Mapping Web Site: Information about lunar geologic mapping can be found at: 

http://astrogeology.usgs.gov/Projects/PlanetaryMap

ping/Lunar/. Included there is information on the 

mapping scheme (Figure 1) and quadrangle layout 

(Figure 2), map projections, digital basemap materials (to be provided by USGS), and useful links 

and references. Digital basemaps will include Lunar Orbiter (LO) photomosaics and/or frames at full 

and reduced resolution [11], and Clementine 

UVVIS (5 bands 400 to 1000 nm; [12]) and NIR (6 

bands, 1100 to 2780 nm; [13]) mosaics. Additional 

optional digital bases include Clementine colorratio images and derived parameters (FeO, TiO2, 

optical maturity; [e.g., 14, 15]), Lunar Prospector 

elemental maps (Fe, Ti, Th, H, etc.; [e.g., 16]), and 

new lunar topographic data [e.g., 17]. Other topical 

basemaps and derived data may be included as 

needed to support the science goals of the mapping 

project. 

Mapping Scheme and Scale: Use of digital 

map bases means that identification of map scale 

and layout scheme for global mapping is less restrictive than in the past. A uniform scale is required for global systematic mapping, and that 

scale must take into account differences in available image resolution and quality for various regions. For example, LO frames are ~60 m/pixel or 

better for the near side and up to 400 m/pixel for 

the far side. If one assumes an ‘average’ pixel 

resolution of 200 m/pixel for the upcoming LO 

global mosaic, then a common mapping ‘rule of 

thumb’ suggests ~10 pixels/mm as the optimal 

resolution for mapping with digital data. At the 

1:2.5 M scale of this lunar mapping program, such 

a mapping resolution translates to 12.5 pixels/mm, 

or slightly higher than optimal. 

 Figure 1. Mapping scheme for lunar geologic maps at 1:2.5 

M scale. The Copernicus quadrangle is marked with an X. 

The image base is Clementine 750-nm albedo. 

Figure 2. Map projections for lunar quadrangles at 1:2.5 M 

scale as defined in this program. 

The 1:2.5 M scale was considered ‘ideal’ for lunar geologic mapping [18], and the Moon is thus 

divided into 30 mapping quadrangles (Figure 1). 

Polar regions are mapped in Polar Stereographic, 

latitudes between 30 ̊ and 60 ̊ in Lambert Conformal Conic, and equatorial quadrangles in Mercator 

projections. At this scale mappers can survey major geologic units, refine unit boundaries and types, 
LUNAR MAPPING PROGRAM: Gaddis et al. 

apply new unit names and contact types where necessary, and map major structures. Quadrangle 

maps at this scale also print at the relatively convenient size of ~21.5”x15” without text. 

Digital Geologic Mapping: Digital mapping 

methods are used in this project, and they are recommended for future lunar mappers as well. Use 

of digital data readily supports image manipulation 

and enhancement, as well as derivation of products 

such as spectral band-depth maps, slope maps from 

topography data, image texture maps, densitysliced albedo and color, etc. Digital mapping 

methods using common drafting and analysis tools 

such as the Geographic Information System (GIS) 

and ‘plug-ins’ by ESRI ArcView are being tested 

and recommendations for their usage will be provided to other mappers. 

Lunar Geologic Mappers’ Handbook: An 

additional product of this pilot program is a handbook for future lunar geologic mappers. Currently 

in preparation, this manuscript will include: (1) a 

summary of major lunar geologic units, stratigraphic correlation [e.g., 19, 20, 21], and processes; 

(2) a history of lunar geologic mapping including a 

summary of current USGS standards (e.g., symbology, contact and structure types); (3) an overview 

of relevant lunar missions and their scientific objectives, instrumentation, and digital data products; 

(4) methods and rationales for lunar geologic mapping with available digital data; (5) detailed information on the digital map bases and ancillary data, 

and how to use both for lunar geologic mapping; 

(6) specific examples of 1:2.5 M-scale mapping, 

including definition and correlation of map units as 

well as identification and characterization of common lunar geologic units and structural features; 

and (7) recommendations for standardized geologic 

unit symbols and nomenclature. This manuscript 

will be published as a USGS Open-File Report 

(online only) and will also be made available on the 

Lunar Geologic Mapping Web site noted above. 

Summary: The ongoing Copernicus quadrangle 

mapping project marks the initiation of a new lunar 

geologic mapping program that takes advantage of 

new data and methods to advance our understanding of lunar geology. Results of this project include (1) a systematic lunar mapping scheme, (2) a 

tested method for formatting and releasing digital 

lunar map bases, (3) a geologic map of the Copernicus quadrangle for publication as a USGS SIMmap, and (4) a lunar geologic mappers’ handbook 

with recommendations on the integration of spectral color, chemistry, mineralogy, elevation, morphology, etc. in the identification and interpretation 

of lunar geologic map units. These products will 

be placed online at the above Web site as resources 

for prospective lunar geologic mappers. 

References: [1] Gaddis et al., 2005, LPS 

XXXVI, #2021. [2] Gaddis et al., 2005, Abst. Plan. 

Mappers Mtg., USGS OFR 2005-1271. [3] Gaddis 

et al., 2005, GSA Ann. Mtg., Abs. 514-4. [4] 

Shoemaker and Hackman, 1962, Symp. 14 IAU, 

289. [5] Schmitt et al., 1967, USGS I-515. [6] Wilhelms and McCauley, 1971, USGS I-703. [7] 

Gaddis et al., 2006, LPS XXXVII, #2135. [8] 

Skinner et al., this volume. [9] Hawke et al., 2006, 

LPS XXXVII, #1133. [10] Hawke et al., this volume. [11] Weller et al., 2006, LPS XXXVII, #2143. 

[12] Eliason et al. 1999, PDS_CL_4001 to _4078. 

[13] Gaddis et al., 2005, NIR PDS archive, in prep. 

[14] Lucey et al., 2000, JGR 105, 20377. [15] Wilcox et al., 2005, JGR-P 110, E11001 [16] Lawrence 

et al., 2006, LPS XXXVII, #1925. [17] Archinal et 

al., 2006, LPS XXXVII, #2310. [18] Wilhelms, 

1972, USGS Interagency Report: Astrogeology 55, 

36 pp. [19] Wilhelms, 1987, USGS Prof. Paper 

1348, 302 pp. [20] Hiesinger et al. 2003, JGR 

108(E7). [21] North American Stratigraphic Code 

1983, AAPG Bull. 67, 841-875. 
THE COMPOSTION AND ORIGIN OF COPERNICUS RAYS: IMPLICATIONS FOR THE 

COPERNICAN-ERATOSTHENIAN BOUNDARY. B.R. Hawke1

, T.A. Giguere1,2, L.R. Gaddis3, B.A. 

Campbell4

, D.T. Blewett5, J.M. Boyce1, J.J. Gillis-Davis1, P.G. Lucey1, C.A. Peterson1, M.S. Robinson6, and G.A. 

Smith1

, 1Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822, 2Intergraph 

Corporation, P.O. Box 75330, Kapolei, HI 96707, 3

U.S. Geology Survey, Astrogeology Program, 2255 N. Gemini 

Drive, Flagstaff, AZ 86001, 4

Center for Earth and Planetary Studies, National Air and Space Museum, Washington, 

D.C. 20560, 5

NovaSol, 733 Bishop Street, Honolulu, HI 96813, 6Center for Planetary Science, Northwestern 

University, Evanston, IL 60208. 

Introduction: The nature and origin of lunar rays 

have long been the subjects of major controversies. 

We have been investigating the origin of lunar crater 

rays in support of the new Lunar Geologic Mapping 

Program. In an effort to better understand the 

processes responsible for the formation of lunar rays, 

we have utilized a variety of remote sensing data to 

study selected rays. Clementine UV-VIS images 

were used to produce high-resolution FeO, TiO2, and 

optical maturity (OMAT) maps for the various rays 

utilizing the methods presented by Lucey et al. [1, 2]. 

Near-IR spectra and 3.8- and 70-cm radar maps were 

also utilized [3, 4]. Our preliminary finding resulted 

in a model for lunar ray formation [5, 6]. It was 

found that lunar rays are bright because of 

compositional contrast with the surrounding terrain, 

the presence of immature debris, or some 

combination of the two. The purpose of this report is 

to present the results of studies of Copernicus rays 

and to assess the implications for the calibration of 

the lunar stratigraphic column. 

The Origin of Copernicus Rays in Mare 

Imbrium: Copernicus is a large bright-rayed crater, 

93 km in diameter, located at 9.5o N, 20.0o W on the 

lunar nearside, and has long been used as a 

stratigraphic marker for lunar geology [7, 8, 9]. 

Continuous ejecta deposits occur up to a crater 

diameter away from the rim crest of Copernicus, 

while the ray system extends radially for more than 

500 km [9]. We have investigated the Copernicus 

rays that extend north across the surface of Mare 

Imbrium with particular emphasis on four major rays. 

Two of these rays (Rays 1 and 2) extend north of 

Copernicus, and two (Rays 3 and 4) extend to the 

northeast. The albedo of the rays varies from 

moderate to high, and all exhibit numerous secondary 

craters which range in diameter from 200 m to 7.0 

km. Many of the secondaries occur in chains or 

clusters that exhibit characteristic V structures or 

herringbone patterns. It has been demonstrated that 

herringbone patterns are formed by the interference 

of ejected materials during the near-simultaneous 

impact of secondary-forming projectiles [9, 10]. In 

the secondary crater clusters, the downrange 

members of the clusters are commonly mantled by 

ejecta or debris surges generated by the uprange 

secondaries.

The rays north of Copernicus (Rays 1 and 2) 

exhibit moderate to strong returns in the 3.8-cm 

depolarized radar image mosaic. The highest values 

are associated with secondary crater clusters. These 

areas have greater abundances of 1- to 40-cm-sized 

fragments in the upper 0.5 m of the regolith. Portions 

of Rays 1 and 2 exhibit slightly enhanced backscatter 

in the depolarized 70-cm radar image. The strongest 

enhancements are associated with secondary crater 

clusters. These enhancements have an excess of 

meter-sized blocks within 5-10 m of the surface. 

The Copernicus rays in Mare Imbrium exhibit 

lower FeO and TiO2 values than do the adjacent mare 

deposits. The background mare flows have FeO 

values that range between 17 and 19 wt.% and TiO2

concentrations that range between 4 and 6 wt.%. The 

rays north of Copernicus have FeO abundances that 

vary from 12 to 16 wt.% and TiO2 values that range 

from 2 to 4 wt.%. The FeO and TiO2 concentrations 

generally show a positive correlation with the albedo 

values exhibited by the ray surfaces. FeO 

abundances generally decrease along a given ray as a 

function of distance from Copernicus. The measured 

FeO value (8.0 wt.%) for the Copernicus ejecta 

blanket can be used to calculate the amount of 

highland-rich primary ejecta in the rays north of 

Copernicus. The calculated abundances of primary 

ejecta range from 20% to 60%. 

The optical maturity (OMAT) images of the 

Copernicus rays indicate that relatively high OMAT 

values are associated with secondary crater chains 

and clusters. The highest values are exhibited by 

steep slopes on the crater interiors. Apparently, 

downslope movement on the interior crater walls 

constantly adds fresh material to the regolith. Ray 

surfaces away from the interiors of secondary craters 

display much lower OMAT values. These OMAT 

values are slightly higher than those exhibited by 

fully mature background mare surfaces near the rays. 

The rays of Copernicus in Mare Imbrium have not 

reached full optical maturity. 

Several faint rays from the crater Eratosthenes 

were identified in Mare Imbrium. These rays exhibit 

lower FeO and TiO2 values than do the adjacent mare 

units and are fully mature. 

In summary, the Copernicus rays in Mare 

Imbrium display relatively low FeO and TiO2 values 
because of the presence of variable amounts of 

highland-rich primary ejecta. The rays exhibit 

relatively low OMAT values except for areas with 

secondary crater clusters. Still, the rays are not fully 

mature. The Copernicus rays are bright largely due 

to contrast in albedo between the ray material 

containing highland-rich primary ejecta and the 

adjacent dark mare surfaces. Only in the vicinity of 

secondary crater clusters and chains does the 

presence of immature, high-albedo material make a 

significant contribution to the brightness of the rays. 

Implications for the CopernicanEratosthenian Boundary: The working distinction 

between the Eratosthenian (E) and Copernican (C) 

Systems is that Copernican craters have visible rays 

whereas Eratosthenian-aged craters do not [7, 11, 

12]. Since compositional rays can persist for 3 Ga or 

more, the mere presence of bright rays is not a 

reliable indicator that a crater was formed during the 

C Period [6, 9, 13, 14, 15]. It is clear that a new 

method is required to distinguish C from E-aged 

craters. It has been suggested that the OMAT 

parameter be used to define the C-E boundary [6, 14, 

15]. With increasing age, the OMAT values for 

ejecta and rays decrease and eventually become 

indistinguishable from the background value, which 

is the optical maturity index saturation point [2, 15]. 

The time required for a fresh surface to reach the 

optical maturity index saturation point could be 

defined as the Copernican Period. Surfaces that have 

reached full optical maturity would then be of 

Eratosthenian (or greater) age. Grier and co-workers 

[14, 15] noted that if the ejecta of Copernicus were 

slightly more mature, it would be indistinguishable 

from the background in an OMAT image. Our 

results for the Copernicus rays in Mare Imbrium are 

consistent with these findings. Hence, the saturation 

of the optical maturity index may occur at about 0.8 

Ga which is the commonly accepted age of 

Copernicus [16, 17, 18]. 

A Reevaluation of Lunar Crater Ages: 

Because of the new definition of the C-E boundary, 

we have investigated the rays associated with a 

number of lunar craters. Our purposes were to 

determine the compositions and maturity states of the 

rays and to assess the ages of the parent craters in 

light of the new criteria. 

Aristillus and Autolycus are located NW of the 

Apollo 15 site. Both have been mapped as 

Copernican craters based on the presence of rays [8, 

12]. The high-albedo rays of Aristillus and 

Autolycus contain highland material and are bright 

because of compositional contrast with the 

surrounding mare terrain. The rays and ejecta of both 

craters have reached full optical maturity. Hence, 

Aristillus and Autolycus are older than Copernicus 

and should be mapped as Eratosthenian-aged craters. 

Taruntius, O’Day, and Eudoxus have been 

mapped as Copernican-aged craters [8, 12]. Our 

results indicate that the rays associated with these 

craters are compositional rays. They are optically 

mature and appear bright only because they contain 

highland debris. These craters are older than 

Copernicus and should be mapped as Eratosthenianaged craters. 

Taruntius H and P are located SE of Taruntius. 

Since these small craters lack well-defined rays, they 

are mapped as Eratosthenian craters [19]. The 

OMAT image of these craters shows that their ejecta 

deposits are immature. They are younger than 

Copernicus and should be assigned a Copernican age. 

 Pytheas has been mapped as a Copernican-aged 

crater [8, 12]. Some portions of the Pytheas ejecta 

deposit exhibit low OMAT values and appear to be 

fully mature. Other portions of the ejecta blanket 

have higher OMAT values. The cause of this 

difference is the subject of a continuing investigation. 

References: [1] Lucey P. et al. (2000) J. 

Geophys. Res., 105, 20,297. [2] Lucey P. et al.

(2000) J. Geophys. Res., 105, 20,377. [3] Zisk S. et 

al. (1974) Moon, 10, 17. [4] Campbell B. and Hawke 

B. (2005) J. Geophys. Res., 110, E09002. [5] Hawke 

B. et al. (2006) LPSC 37, #1133. [6] Hawke B. et al. 

(2004) Icarus, 170, 1. [7] Shoemaker E. and 

Hackman R. (1962) The Moon-Sym. 14 of the I.A.U., 

289. [8] Wilhelms D. and McCauley J. (1971) 

U.S.G.S. Map I-703. [9] Pieters C. et al. (1985) J. 

Geophys. Res., 90, 12,393. [10] Oberbeck V. and 

Morrisson R. (1973) Proc. Lunar Sci. Conf., 4th, 107. 

[11] Ryder G. et al. (1991) Geology, 19, 143. [12] 

Wilhelms D. (1987) U.S.G.S. Prof. Pap., 1348. [13] 

McEwen A. et al. (1993) J. Geophys. Res., 98, 

17,207. [14] Grier J. and McEwen A. (2001) 

Accretion of Extraterrestrial Material Throughout 

Earth History, 403. [15] Grier J. et al. (2001) J. 

Geophys. Res., 106, 32,847. [16] Eberhardt P. et al. 

(1973) Moon, 8, 104. [17] Bogard D. et al. (1994) 

GCA, 58, 3093. [18] Stoffer D. and Ryder G. (2001) 

Space Sci. Rev., 96, 9. [19] Olson A. and Wilhelms 

D. (1974) U.S.G.S. Map I-837. 
PROGRESS ON MAPPING THE COPERNICUS 1:2,500,000-SCALE QUADRANGLE ON THE 

MOON: IMPACT CRATER FACIES AND MINERALOGIES. J.A. Skinner, Jr., L.R. Gaddis, and K. 

L. Tanaka. Astrogeology Team, U.S. Geological Survey, Flagstaff, AZ 86001 (jskinner@usgs.gov). 

Introduction: The first systematic lunar geologic maps were completed at 1:1M scale for the 

lunar near side during the 1960’s using telescopic 

and Lunar Orbiter (LO) photographs [1-3]. Later, 

global mapping of the Moon was accomplished at 

1:5 M scale [4-9], and smaller scale maps were 

made for sites of ‘scientific interest’ (including the 

Apollo landing sites) using orbital and in situ data 

[e.g., 10]. Geologic mapping of the Copernicus 

crater (dia. 95 km) region was performed by Shoemaker and Hackman [11], Schmitt et al. [1], and 

Howard [10]. Numerous topical studies have since 

considered the origin, distribution, and composition 

of geologic units within this region [e.g., 12-14]. 

Here we describe progress in the pilot lunar 

mapping project, which not only addresses the geologic units and history of the Copernicus quadrangle (0-30°N, 0-45°W) but is also intended to evaluate the utility of existing data and outline the processes and precedents that should be implemented in 

future systematic mapping. Following our reconnaissance-level mapping, we now focus our efforts 

on detailed delineation and discrimination of geologic units. Our current emphasis is on integrating 

color and mineralogic information with “classical” 

morphogeologic crater units to better discriminate 

impact-related materials and facies. This approach 

is relevant because the region contains type localities for crater-related units and major stratigraphic 

divisions. Our mapping is guided by recent characterization of the Copernican-Eratosthenian lunar 

stratigraphic boundary using Clementine-derived 

optical maturity (OMAT) data [e.g., 15]. 

Geologic Setting: The Copernicus quadrangle is 

dominated by high-albedo units of the young (~0.8 

Ga) Copernicus crater. These are superimposed on 

older basin rim and ejecta units of Imbrium basin 

(highlands of Montes Carpatus), as well as old or 

intermediate-aged highlands, mare, pyroclastic and 

impact crater (e.g., Eratosthenes, dia. 58 km) units. 

Mapped geologic units within the quadrangle include the oldest, Lower Imbrian materials of Imbrium basin (Alpes and Fra Mauro Fms.), Upper 

Imbrian mare basalts, cones, dark-halo craters and 

pyroclastic deposits (Mare Insularum, Sinus Aestuum, and SE Mare Imbrium), Eratosthenian mare 

basalts (central Mare Imbrium) and crater materials, 

and young Copernican impact and related deposits. 

Data: We processed, orthorectified, and coregistered data using image processing (ISIS) and GIS 

(ArcMAP) software. All digitization was completed 

in an ESRI geodatabase format to simplify data 

compilation, vector attribution, topological cleaning, interlayer analyses and data sharing. Basemaps 

include a LO-IV photomosaic (60 m/px; [e.g., 16]), 

Clementine 5-band UVVIS (100 m/px, [17]) and 6-

band NIR data (500 m/px, [18]) and derived maps 

of iron [19] and titanium, Clementine-derived topographic data [20], Earth-based 3.8 cm radar (3.1 

km/px; [21]), and OMAT [19, 22]) data. We also 

use high (9 m/px) and very-high (1.3 m/px) resolution LO-IV frames of the Copernicus crater floor, 

wall, and central peak [16]. 

Current lunar geologic mapping is performed in 

the context of previous studies but also takes advantage of new digital data for the Moon. Integration of historical mapping products and more recent 

investigations is challenging, and requires complementing standard mapping methods and conventions based on morphology, texture, and albedo 

with mineralogic and lithologic information derived 

or inferred from Clementine 11-band color and 

other data. 

Mapping Scale and Feature Size: At 1:1M 

scale [1], Copernicus crater units and features were 

mapped at sizes down to 2 mm (2 km on the 

ground), and numerous (but not all) secondary craters were mapped. At 1:2.5M scale, we map features down to 2 mm in size (5 km on the ground). 

Because many of the Copernicus secondary craters 

are at or just less than 5 km in size, they will not be 

identified in our mapping; those greater than 5 km 

in size are identified by a symbol. Major secondary 

crater chains are mapped as discrete units (e.g., feature formerly named Rimae Stadius). Minor secondary scatters and chains are identified by a crater 

ray pattern. Overlapping rays of Copernicus, Kepler, and Aristarchus craters are not differentiated 

within the mapped ray patterns. Following the lead 

of Schmitt et al. [1], we do not discriminate secondary rays, craters, or materials when they superpose 

primary rim materials of the parent impact. 

Crater Units: Geologic units of Copernicus crater include wall, floor, and central peak materials, 

impact melt deposits, ejecta morphologies, and numerous secondary rays and craters [1, 10, 12]. With 

Clementine color, particularly derived maps (e.g., 

FeO and OMAT) and color-ratio images, we can 

more accurately map the extent of excavated materials and identify the potential type lithology of material being excavated and redistributed. Objectively balancing criteria for morphologic unit identification with those for color or spectral units has 

proven to be a challenge. 

Morphologic Unit Criteria. “Classical” crater 

units are divided by crater location (e.g., rim, wall, 

floor) and then subdivided into surface texture and 

morphology (e.g., hummocky, smooth, radial). The 

result is a unit symbol (e.g., Ccrh) that designates 

age (e.g., Copernican age--C), material type (e.g., 
crater-related material--c), unit (e.g., rim material--

r), and sub-unit (hummocky--h). Spectral data permit us to advance beyond pure “morphostratigraphic” mapping, allowing units and subunits to 

be divided by morphology and spectral characteristics. Morphology-dependent units have been described as problematic and not entirely correlative 

to the emplacement process [23-24]. Thus we avoid 

naming units based on morphology alone (for example, "Ccrh--Copernican-age, crater unit, rim subunit, hummocky member), opting instead for "Ccra- -Copernican-age, crater unit, rim sub-unit, member 

a". Using this convention, although Copernicus and 

Kepler craters have correlative morphologic units, 

they can be discriminated on the basis of their distinctive spectral properties. 

Mineralogic Unit Criteria. Clementine data 

show substantial variation in optical maturity, reflectance, and morphology among deposits from 

Copernicus and Eratosthenes craters. For example, 

the northwest crater floor, wall, and ejecta blanket 

of Copernicus have significantly elevated 750-nm 

values (herein deemed a proxy for albedo), indicating excavation and redistribution of a bright material. This unit has been mapped as glass-rich, impact melt that ponded on the floor and draped the 

walls and ejecta [e.g., 10]. These bright regions are 

inferred to be comprised of a low-iron material excavated from a highlands unit at depth. A broad 

heterogeneity in color of wall, floor, and ejecta 

units of Copernicus crater indicates that materials 

are diverse in composition and, in some locations, 

were not intimately mixed during crater formation. 

No thorium enrichment is observed for Copernicus 

[e.g., 25], so a local ‘KREEP-rich’ rock unit is not 

likely to be present. Eratosthenes crater, which 

partly overlies highlands units of Imbrium basin 

rim deposits, shows a comparable but more subdued color variation, suggesting that the northernmost ejecta may contain materials from excavated 

pre-Imbrium (Nectarian) basement rocks. 

Color data also provide an ability to distinguish 

between craters that have penetrated through impact ejecta into underlying mare basalts (i.e., darkhalo craters such as Copernicus H) and those that 

have penetrated further to the deepest highlands 

units. Such craters provide information on the 

stratigraphy, thickness, and distribution of underlying geologic units. Derived OMAT data have also 

allowed us to re-evaluate relative ages of craters in 

this region and to assign new, Eratosthenian (older) 

ages to craters Aristillus, Autolycus, Taruntius, 

O’Day, Eudoxus and possibly Pytheas [15]. 

The integration of Clementine color data means 

that we must modify and adapt previous mapping 

conventions. For example, we divide materials that 

have distinct morphologic textures, stratigraphic 

(cross-cutting) relationships, and spectral characteristics into distinct geologic units. When color or 

spectral signatures vary among units within a single 

formation, a ruled and dashed pattern is used to indicate subdivided units. To avoid overlapping patterns, we group key mineralogic characteristics together when possible. Units with comparable 

ranges of iron, titanium, or optical maturity values 

can be grouped together and indicated with unit 

patterns (e.g., "low OMAT", "low Fe", "high 

TiO2"), in much the same way ruled and dashed 

patterns were used by Schmitt et al. [1] to discriminate three albedo ranges (e.g., high, medium, and 

low). Though Clementine raster maps allow us to 

quantify spectral unit characteristics, we use this 

information primarily as a supplement to geologic 

observations and measurements. 

Plans: We will present a map for review within 

the project team by the end of CY06. During map 

review, we will complete a Lunar Geologic Mapper’s Handbook that will (1) address data specifics 

(e.g., instrumentation, processing, projection, limitations), (2) outline stratigraphic and unit precedent, 

and (3) explore methods for hard-copy presentation 

(e.g., correlation of map units). We intend to have 

the Handbook rigorously reviewed by a host of 

planetary geologists whose combined experience 

and expertise in lunar and planetary science will 

help pave the way for the complete, systematic 

1:2.5M-scale geologic mapping of the lunar surface. 

References: [1] Schmitt et al., 1967, USGS I515 (LAC-58). [2] Wilhelms and McCauley 1971, 

USGS I-703. [3] Shoemaker and Hackman, 1962, 

Symp. 14 IAU, 289. [4] Wilhelms and McCauley, 

1971, USGS I-703. [5] Lucchitta, 1978, USGS I1062. [6] Wilhelms et al., 1979, USGS I-1162. [7] 

Wilhelms and El-baz, 1977, USGS I-946. [8] Scott 

et al., 1977, USGS I-1034. [9] Stuart-Alexander, 

1978, USGS I-1047. [10] Howard, 1975, USGS I840. [11] Shoemaker and Hackman, 1962, Symp. 

14 IAU, 289-300. [12] Pieters et al., 1985, JGR 90, 

12393-12413. [13] Gaddis et al., 1985, Icarus 61, 

461-489. [14] Zellner et al., 2002, JGR 107. [15] 

Hawke et al., this volume. [16] Weller et al., LPSC 

37. [17] Eliason et al. 1999, PDS Vol. 

USA_NASA_PDS_CL_4001 to 4078. [18] Gaddis 

et al., 2006, PDS archive (in prep.). [19] Lucey et 

al., 2000, JGR 105, 20377-20386. [20] Archinal et 

al., LPSC 37. [21] Zisk et al., 1974, The Moon, 17-

50. [22] Wilcox et al., 2005, JGR 110. [23] Hansen 

2000, EPSL 176, 527-542. [24] Tanaka et al. 2005, 

USGS SIM 2888, 1:15 M scale. [25] Gillis and Jolliff, 1999, New Views of the Moon II. 
GEOLOGIC MAPPING OF HIGHLAND/LOWLAND BOUNDARY ZONES: EASTERN HELLAS 

PLANITIA AND DEUTERONILUS MENSAE, MARS. David A. Crown, Leslie F. Bleamaster, III, and Frank 

C. Chuang, Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, crown@psi.edu. 

Introduction: Geologic mapping investigations of 

Hellas Planitia at the eastern margin of Hellas basin 

and of Deuteronilus Mensae at the northern margin of 

Arabia Terra provide new constraints on the styles and 

timing of the diverse processes that have shaped the 

complex geologic records preserved in these highlandlowland boundary zones. Current mapping studies 

build on previous geologic mapping in eastern Hellas 

[1-10] and recent analyses of debris aprons in eastern 

Hellas and along the dichotomy boundary [11-13]. 

Eastern Hellas Planitia: This map area includes 

parts of Dao and Harmakhis Valles and their floor 

deposits, possible remnants of basin rim materials, 

dissected and channeled plains, and deposits associated 

with the Hellas basin floor. Following the mapping 

precedents of [3, 8], materials in MTM -40277, -45277, 

and -45272 (and -40272 [8]) quadrangles have been 

divided into two major geologic assemblages: the 

Hellas rim assemblage and the Hellas floor 

assemblage. The contact between these assemblages 

occurs near the -5800 meter topographic contour. At 

1:5M scale, materials above -5800 m were mapped as 

the Hesperian/Noachian dissected unit, member 1; 

below -5800 m, materials were mapped as the 

Hesperian smooth interior unit [3]. Mapping at 1:1M 

scale by Price [8] subdivided the dissected unit into 

Hesperian smooth plains (unit Hps) and Hesperian/ 

Noachian hummocky plains (unit HNh). 

Hellas rim assemblage. Two areally expansive 

units (units HNh and Hps) surround the distal portions 

of the Dao and Harmakhis Valles canyon systems. 

Using THEMIS IR and VIS data, we have evaluated 

the contacts of units Hps and HNh mapped by Price [2] 

and have extended these unit boundaries from MTM 

-40272 to the rim/planitia boundary. Hummocky plains 

(unit HNh) display 10s to 100s of meters of relief and 

appear to be exposed by removal of the upper smooth 

plains surface (by either down cutting from channels, 

scarp retreat and aeolian erosion, and/or collapse from 

loss of volatiles). Smooth plains (unit Hps) are 

correlated with the locations of small-scale surface 

channels, which may be the first stage in canyon 

development and hummocky plains exposure. It is 

unclear if the channels are responsible for emplacing 

the smooth plains (i.e., bank-full deposits) or channels 

cut the smooth plains and are only preserved within 

them; most likely both circumstances exist. The larger, 

more mature, canyon segments of Dao and Harmakhis 

Valles also dissect the rim assemblage; the lower 

reaches of Dao Vallis preserve several episodes of 

channel/canyon development showing abandoned 

truncated channels (units ch1 and ch2). Where the 

canyons are wide and more fully developed, 

Amazonian/Hesperian valley fill superposes their 

floors (units vd and vh). 

Using MOC images, we systematically searched 

the map region for layered materials; results indicate 

that finely-layered outcrops are concentrated along the 

scarp that defines the eastern edge of the basin. 

Outcrops are exposed in locally high standing mesas, 

knobs, and surfaces near -5700 m within hummocky 

plains. Consistent elevations and spatial associations 

among unit contacts of these layered deposits suggest 

that the isolated layered outcrops most likely represent 

remnants of a once laterally continuous deposit of the 

smooth plains (unit Hps) that was part of a more 

widespread depositional shelf in eastern Hellas [14]. 

Hellas floor assemblage. Hellas floor materials are 

moderately to heavily cratered, deformed by polygonal 

wrinkle ridges, and are locally dissected by the farthest 

extensions of Dao and Harmakhis Valles. With the 

exception of a lobe extending from the mouth of Dao 

Vallis (unit vt), there is a general lack of distinct 

depositional margins/contacts in the vicinity of channel 

and canyon mouths that cross the rim/floor assemblage 

contact. This suggests that eastern Hellas floor 

materials 1) are far reaching deposits from Dao and 

Harmakhis Valles with contacts west of the map area, 

2) are not comprised of significant materials delivered 

by Dao and Harmakhis Valles, or 3) that both the floors 

of the canyons and Hellas have undergone significant 

Amazonian resurfacing (mass movements and aeolian 

infill), which has masked any original genetic and/or 

temporal relationships between canyon floor and 

Hellas floor materials. 

Near the mouth of Harmakhis Vallis, relatively 

deep sinuous depressions extend from the mouth of 

Harmakhis Vallis and meander around high standing 

plateaus. These depressions do not preserve primary 

channel features but do maintain a characteristic 

planform shape indicative of fluvial processes, 

supporting hypothesis 3 as described above. The 

subdued topography of these depressions and the 

surrounding plateaus suggests burial by meters to 100s 

of meters of material. The deepest portions of these 

depressions exhibit the smoothest materials, perhaps 

indicating the greatest degree of burial (units bfs and 

bfh). These farthest extensions of Harmakhis Vallis 

may or may not represent ancient surface connections 

between the Harmakhis head valley and its terminus. 

The plateaus in this region preserve trends consistent 

with wrinkle ridge trends to the south of the sinuous 

depressions. There is no topographic expression of any 

wrinkle ridge across the depressions, suggesting that 

topography associated with the wrinkle ridges and 

plateaus was established prior to the excavation of the 

channel-like features. Thus the surfaces of the plateaus 

and the plains to the south most likely represent the 

same surface (unit sia). 

South of this plateau region are several large 

craters with commingled ejecta blankets. Some ejecta 

blankets display radial striations and lobate margins. A 

variety of degradation states are evident, consistent 

with various ages of the impact events; however, the 

exposed surface is dominated by armored ejecta 

blankets with few superposed pristine craters 

suggesting that this surface was potentially buried and 

has since been exhumed in a relatively uniform 

manner. Several crater rims merge with both 
pronounced and subdued topography associated with 

the regional wrinkle ridges, making this region older 

than the deformation, and potentially the oldest area 

within the map area. 

In the SE corner of the map area, the division 

between the rim and floor assemblages is not as clear 

as it is expressed as a much less pronounced facies 

transition. The rim to floor gradient is more gradual 

than the sharp depositional shelf margin in the north; 

however, the -5800 m contour still marks a 

morphologic change. Ridge trends trace across this 

gradational boundary, but to the east of the contour, the 

surface is smooth and displays superposed channels 

(unit pc), whereas the west lacks channels and contains 

many small to medium-sized craters (unit sia). 

Deuteronilus Mensae: MTM 35337, 40337, and 

45337 quadrangles contain the transition from Arabia 

Terra highlands to lowland plains of Acidalia Planitia. 

Deuteronilus Mensae as a whole has been included in 

previous mapping at 1:5M [15] and 1:15M scales [16-

17], and McGill [18] mapped a N-S swath of MTM 

quadrangles to the east. MTM quadrangle 35337 

consists of cratered terrain exhibiting ~8 craters ≥15 

km in diameter, including the 125 km-diameter crater 

Cerulli. Large craters show a range of preservation 

states but are mostly moderately to highly degraded. 

MTM quadrangles 40337 and 45337 contain the 

transition from relatively continuous highland surfaces 

into the fretted terrain where uplands are preserved in 

mesas surrounded by low-lying plains and debris 

aprons. Parts of fretted terrain valley systems 

(including Mamers Valles), the large low-lying 

expanse containing Deuteronilus Colles, and the 

angular mesas and surrounding lowlands of 

Deuteronilus Mensae proper are also included. Crater 

Lyot is located to the NE and its ejecta should have at 

one time covered the area exposed in MTM 45337. 

Parker et al.’s [19] analysis of Deuteronilus Mensae to 

the west suggests the presence of two gradational 

boundaries that may be associated with ancient Martian 

northern oceans. 

From analyses of Viking Orbiter, THEMIS IR and 

VIS, and MOC images coupled with MOLA 

topography, preliminary mapping of MTM 35337, 

40337, and 45337 quadrangles has been completed. In 

the map area, the continuous highland terrain of 

northern Arabia Terra has been divided into two units 

(plateau material and dissected plateau material) based 

on the degree of modification by fluvial activity in the 

form of small, sinuous channels. Plateau material 

exhibits several large elongated depressions that 

contain blocks of the surrounding materials, suggesting 

the initial stages of surface collapse above a volatilerich zone. Numerous craters are evident within the 

highland terrains, often with multiple lobes of ejecta. 

The materials associated with Cerulli crater are mapped 

separately, given their large areal extent; radial 

grooves, secondary crater fields, sinuous channels, and 

small superposed impact craters are shown. Remnants 

of the highland plateau are preserved to the north as 

individual and clustered polygonal mesas, typically 

with flat upper surfaces. Division into lower and upper 

mesa materials is based on consistent differences in 

albedo and elevation, presumably reflecting 

stratigraphic layers within the highland plateau. Lowlying materials surrounding mesa materials have been 

mapped as mottled, knobby, and smooth plains. 

Deuteronilus Colles, interpreted to be the eroded 

remnant of a crater interior structure, includes 

individual and clustered, irregularly-shaped, rounded 

knobs ranging from 100s of meters to a few kilometers 

across (Deuteronilus Colles material) and smooth to 

hummocky deposits with lobate margins adjacent to 

knobs (Deuteronilus Colles apron material). Numerous 

debris aprons are apparent in the central and northern 

parts of the map area. These occur as smooth lobate 

deposits that surround and extend from the bases of 

mesas, knobs, degraded crater rims, and fretted valley 

walls. The surfaces of debris apron material often have 

lineations parallel or transverse to the apparent flow 

direction. Multiple overlapping aprons in a given 

locality are common. Apron surface slopes in the map 

area are gentle, ranging from 0.4 to 6.6°. Debris apron 

materials clearly post-date the formation of mesas and 

appear to also post-date formation of the low-lying 

plains and medium to large impact craters in the 

region. 

In addition to the debris aprons, there is additional 

evidence for young resurfacing in the region, at least 

on a local basis. Smooth fill material, observed 

between blocks of plateau material in collapse 

depressions and within the floors of impact craters, is 

interpreted to be debris resulting from complete 

breakdown of collapsed blocks. Hummocky fill 

material consists of small knobs and associated smooth 

deposits with lobate margins on the floors of collapse 

depressions and may represent a less complete state of 

degradation. Grooved fill material exhibits a series of 

concentric surface lineations and occurs in crater 

interiors (i.e., concentric crater fill). The surface 

lineations observed on debris aprons and certain fill 

deposits are consistent with a volatile-rich substrate 

during at least the later stages of the geological history 

of the region. 

References: [1] Crown D.A. et al. (1992) Icarus, 100, 1-

25. [2] Mest S.C. and Crown D.A. (2001) Icarus, 153, 89-110. 

[3] Leonard G.J. and Tanaka K.L. (2001) USGS Geol. Invest. 

Ser. Map I-2694. [4] Tanaka K.L. and Leonard G.J. (1995) 

JGR, 100, 5407-5432. [5] Greeley R. and Guest J.E. (1987) 

USGS Geol. Invest. Ser. Map I-1802B. [6] Mest S.C. and 

Crown D.A. (2002) USGS Geol. Invest. Ser. Map I-2730. [7] 

Mest S.C. and Crown D.A. (2003) USGS Geol. Invest. Ser. 

Map I-2763. [8] Price K.H. (1998) USGS Misc. Invest. Ser. 

Map I-2557. [9] Mest S.C. and Crown D.A. (2005 in press) 

USGS. [10] Crown D.A. and Greeley R. (2005 in USGS edit) 

USGS. [11] Pierce T.L. and Crown D.A. (2003) Icarus, 163, 

46-65. [12] Mangold N. (2003) JGR, 108, doi: 10.1029/ 

2002JE001885. [13] Chuang F.C. and Crown D.A. (2005) 

Icarus, 179, 24-42. [14] Crown D.A. et al. (2005) JGR, 110,

E12S22. [15] Lucchitta B.K. (1978) USGS Misc. Invest. Series 

Map I-1065. [16] Greeley R. and Guest J.E. (1987), USGS 

Misc. Invest. Series Map I-1802-B. [17] Tanaka K.L. et al. 

(2005) USGS Scientific Invest. Series Map I-2888. [18] McGill 

G.E. (2002) USGS Geol. Invest. Ser. Map I-2746. [19] Parker 

T.J. et al. (1989) Icarus, 82, 111-145. 
MAPPING MARGARITIFER TERRA: MTMS -15017, -20002, -20007, -20017, -20022, -25002, -25007. C. M. 

Fortezzo1,2, K. K. Williams1

, and J. A. Grant1, 1Center for Earth and Planetary Studies, National Air and Space 

Museum, Washington, DC, 20013-7012, 2

Northern Arizona University, Flagstaff, AZ, 86001. cfortezzo@si.edu 

Introduction: As part of a continuing campaign to 

better understand the relationship between valleys 

and resurfacing events through mapping, we are 

mapping seven 1:500,000-scale MTM quads in the 

Margaritifer Terra region. Results from this mapping 

will also help constrain the role and extent of past 

water in Margaritifer Terra. The MTMs are grouped 

in two different areas (Figure 1, red boxes with black 

text) within the region and compliment the completed 

mapping in four quads (Figure 1, red boxes with 

hatch pattern) that are currently in the review process 

[1-4]. 

Three western quads focus on Jones crater and the 

Himera, Samara and Loire Valles systems (central 

portion of figure 1). The four eastern quads focus on 

the headward regions of Paraná Valles and the 

valleys on the western flank of Newcomb crater 

(southeast area of Figure 1). 

Datasets: For these maps, we used MDIM 2.1 

and MOLA 128 pix/deg datasets as the initial 

mapping base. In addition, we processed THEMIS 

daytime and nighttime infrared images and overlaid 

both sets on MDIM 2.1 and used them as a mapping 

base with ~95% coverage. THEMIS daytime and 

nighttime infrared images were processed using the 

ISIS-based THEMIS processing website (themproc.mars.asu.edu) and overlain in ArcMap. 

Regional-scale map bases are supplemented with GIS 

hotlinked THEMIS visible and MOC narrow angle 

images where available. 

Methods: We have imported and registered all 

pertinent raster and vector data using ESRI’s ArcMap 

GIS software. Using this digital environment, we 

have begun digitizing lines (e.g., contacts, structures, 

etc.) and polygons (e.g., units and craters). Arc 

extensions provide robust tools for (1) analyzing 

spatial relationships across multiple data layers, (2) 

attributing and updating digital linework, (3) building 

and analyzing vector topologies, and (4) importing 

new data as they are released. To inspect and 

quantify stratigraphic relations, we are compiling 

crater counts in ESRI’s ArcView GIS software to 

make use of crater counting tools [5] specifically 

developed for planetary mappers [6]. 

Current Work: Work on the seven quads began 

by concentrating on the Newcomb-Paraná area 

Figure 1: Shaded relief overlain by MOLA 128 pix/deg of Margaritifer Terra. Arrows point to the locations of 

prominent features. The red boxes indicate MTM quads. Red boxes with black numbers are the 7 quads 

currently being mapped and boxes with a hatch pattern and white numbers indicate quads submitted for review. 
(MTMs -20002, -20007, -25002, and -25007; Figure 

3) in order to determine the relative ages of 

resurfacing events in upper Paraná Valles and to 

examine how valleys either incise or are mantled by 

resurfacing deposits within the Newcomb-Paraná 

region. 

The Jones crater area (MTMs -15017, -20022, and 

-20017; Figure 2) covers an L-shaped area from 

Himera Valles, around Jones crater, to Loire Valles 

(Figures 1 and 2). Current work in this area involves 

counting craters and demarcating initial units. 

Future Work: For both areas, geologic linework 

advances as the science tasks are started. 

In the Jones crater area, review of Viking Orbiter 

images led to the hypothesis that the drainage history 

of the Jones-Loire area may have been affected by 

emplacement of Jones crater [7]. Ejecta from Jones 

crater partially buries parts of Samara and Loire 

Valles and totally obscures portions of Samara Valles 

[7]. We will test the hypothesis that a second order 

pathway once connected Samara Valles with Loire 

Valles east of the third ring of the Ladon basin using 

higher resolution MOC and THEMIS images, MOLA 

topography and the 1:500,000 map. 

Figure 3: THEMIS daytime and nighttime 

infrared image mosaic of the Newcomb-Paraná 

area. 

In the Newcomb-Paraná area, crater counting 

techniques designed for calculating the ages of 

narrow, linear features [8, 9] will be used to establish 

comparative ages of the valley networks relative to 

each other. This analysis will be performed on the 

Paraná Valles network and on the network on the 

western flank of Newcomb crater, and the results of 

each area will be compared to determine their ages 

relative to each other. We will compute the 

cumulative crater densities for sub-basins within the 

valley networks and compare them against each other 

to further constrain the role and persistence of water 

in the region. 

If the results of crater counts show that valley 

networks formed simultaneously, it may suggest that 

groups of basins and sub-basins over a region are 

related, suggesting an areally extensive period of 

water-driven erosion. However, Paraná Valles and 

the valley network on the west flank of Newcomb 

crater do not currently display linked valleys at the 

surface, but it is possible that they were linked 

hydrologically in the past. One possible scenario is 

that the valley networks could have been connected 

when they were active but evidence of their 

connection is obscured by later resurfacing events 

(i.e. volcanic resurfacing or crater impacts\ejecta). 

The second scenario is that the valleys are not linked 

at the surface but are linked by a groundwater 

network. This hypothesis will be tested by attempting 

to create a groundwater flow model using discharge 

rates from active sapping systems on Earth and 

scaling the model with Martian physical properties. 

Figure 2: THEMIS 

daytime infrared image 

mosaic of the L-shaped 

Jones crater area. Gaps in 

the dataset are areas 

where there is currently 

no released THEMIS 

daytime IR coverage. 

References. [1] Grant J.A. and D.A. Clark (2002) 

Planetary Mappers Meeting (abst.). [2] Williams, 

K.K. and J.A. Grant (2003) Planetary Mappers 

Meeting (abst.). [3] Fortezzo, C.M. and J.A. Grant 

(2004) Planetary Mappers Meeting (abst.). [4] Grant, 

J.A., K.K. Williams, and C.M. Fortezzo (2005) 

Planetary Mappers Meeting (abst.). [5] Hare, T. et al. 

(2006) LPSC XXXVII, 2398 (abst.). [6] Barlow, N. 

(2006) LPSC XXXVII, 1337 (abst.). [7] Grant, J.A. 

(1987) NASA Tech, Memo., 89871, 1-268. [8] 

Tanaka, K.L. (1982) NASA Tech. Memo., 85127, 

123-125. [9] Wichman, R. and P.H. Schultz (1987) 

NASA Tech. Memo., 89810, 474-475. 
GEOLOGIC MAPPING OF OLYMPUS MONS CALDERA, MARS, AT 1:200K. 

Peter J. Mouginis-Mark, HIGP/SOEST, University of Hawaii, Honolulu, HI 96822 

A 1:200K geologic map of Olympus Mons caldera will be produced, using both 

THEMIS VIS and HRSC images. By mapping each of the other craters within the 

caldera, we will be able to examine the possible differences in intra-caldera activity at 

different times in the evolution of the caldera. Understanding the spatial distribution of 

the tectonic and volcanic features within Olympus Mons caldera via the new map will 

have importance for future research efforts that will either be proposed by us to PG&G or 

MDAP, or by others who could use the map for input data for thermal models that 

explore the longevity of the magma source (e.g., Wilson et al., 2001). 

Figure 1: Base-maps of the coverage for Olympus Mons caldera that we have assembled for this mapping 

effort. At left is a mosaic of 15 individual THEMIS VIS images at a resolution of 18 m/pixel. At right is 

the Mars Express coverage provided by orbit 037. These two images will serve as the geodetic control for 

all of the GIS layers that are produced under this mapping effort. 

Progress in Year 1 

1) We have assembled the map base from the THEMIS VIS images, co-registered 

these images with the Mars Express data (Figure 1), and converted these images to the 

mapping projection. The two data sets provide complimentary coverage of the caldera by 

virtue of the higher spatial resolution of the Mars Express scene and the more suitable 

(i.e., lower) sun angle of the THEMIS data. All of the GIS data products to be generated 

during this mapping will be referenced to this image data base. 

2) Initiate investigations of secondary craters on the caldera floor as a precursor to 

the development of crater counts based on the available MOC images. This is an 

important precursor to the development of a chronology for the collapse events that now 

form the six main craters that comprise the caldera. We are particularly concerned about 

this relative timing of the caldera collapse events in the light of the results from Mars 

Express (Neukum et al., 2004) that propose a sequence of collapse that is contrary to the 

stratigraphic sequence of the craters. To this end, part of our work in Year 1 has been to 

examine all of the MOC images of the caldera floor to identify probable secondary 
craters from the 14 km diameter impact crater on the southern rim. The results from our 

search are shown in Figure 2. 

Figure 2: Distribution of secondary craters from the impact crater Pangboche (name provisionally 

approved by the IAU) to the south of the caldera rim (shown “a” at left). Preliminary mapping conducted 

under this effort (“b”) shows that these secondary craters extend across most of the caldera floor and are 

most likely responsible for the old ages inferred by Neukum et al. (2004). Center image shows the 

locations of these secondary craters and the locations of the two MOC images. At right (“c”) the arrows 

identify some of the larger clusters of secondary craters. a) Part of MOC image E0701134; c) part of MOC 

image R0700514. 

Plans for Year 2

a) Conduct the crater counts, discounting the secondary craters shown in Figure 2 in 

order to derive a relative chronology for the caldera collapse events. 

c) Complete a draft geologic map of the entire Olympus Mons summit area, and 

submit this map to the U.S. Geological Survey for preliminary review. 

d) Publish a research paper (either in JGR-Planets or Icarus) on the similarities and 

differences between caldera subsidence at the different craters within the Olympus 

Mons caldera. 

e) Start to write the accompanying map text. It is not yet known if we will just have 

text on the side of the formal map, or whether there will be sufficient information to 

make this a supplement to the map. 

f) Explore options for the production of supplemental map materials, such as slope 

and aspect maps from MOLA. 

References 

Neukum, G. and 10 others (2004). Recent and episodic and glacial activity on Mars revealed by 

the High Resolution Stereo Camera. Nature 432: 971 – 979. 

Wilson, L., E.D. Scott and J.W. Head (2001). Evidence for episodicity in the magma supply to 

the large Tharsis volcanoes. J. Geophys. Res. 106: 1423 - 1433. 
1:200K GEOLOGIC MAPPING OF THE MARTIAN IMPACT CRATER 

TOOTING. Peter J. Mouginis-Mark, HIGP/SOEST, University of Hawaii, Honolulu, HI 

96822

Impact craters provide crucial information on the subsurface structure of the target 

material, as well as insights into the cratering process. In the case of impact craters on 

Mars, the three-dimensional structure of a crater is particularly important as it may 

provide evidence for spatial or temporal variations in the distribution of volatiles. 

Mouginis-Mark et al. [2003] identified a 29 km diameter crater at 23.2°N, 207.8°E that 

meets many of the criteria for having formed in the very recent past. This crater (Fig. 1), 

provisionally named “Tooting”, lies to the west of the Olympus Mons aureole, and 

formed in relatively young lava flows from the volcano. Analysis of Tooting crater not 

only provides information on the original geometry of large impacts on Mars, but also 

enables the original morphology of the crater cavity and ejecta layers to be examined. 

We have just started a new 1:200K geologic map of Tooting crater in order to better 

understand the geologic history and spatial distribution of units. A 1:1M map of the 

secondary crater field of Tooting will also be produced. In this way, we hope that our 

maps will further the understanding of the morphology of a very fresh, large, impact 

crater on Mars in much the same way that the map of the crater Copernicus [Howard, 

1975] promoted a better understanding of fresh large lunar craters. We have three goals 

for this mapping: 

1) Mapping the secondary crater field: Tooting has a large number of secondary craters 

that are located right next to the distal rampart of the ejecta lobes (indeed, it seems highly 

likely that some secondaries are buried by the ejecta lobes). This distribution of 

secondaries is strikingly different from that of Zunil where most of the secondaries are at 

large radial distances from the primary [McEwen et al., 2005], and so we hope that by 

producing a 1:1M scale map of the secondary crater field of Tooting we will be able to 

document the proximal segment of a large secondary crater population. 

2. Geology of the crater cavity: Understanding the pristine geology of any impact crater 

on Mars that is several tens of kilometers in diameter has great value by virtue of the fact 

that it sets a benchmark against which other, older and more degraded, craters can be 

compared. We believe that we can identify several features within Tooting that set such 

constraints for the impact cratering process on Mars. These features include: (a) blocks 

on the crater floor that may be segments of a large central peak; (b) impact melt sheets on 

the southern portion of the floor; and (c) lobes of material that may be impact melt on the 

southern outer rim. The possible identification of impact melt is particularly intriguing 

as numerical models for the effects on volatiles on Mars would predict that melt would 

be rapidly destroyed during the cratering process (Kieffer and Simonds, 1980). 

3. Mode of ejecta emplacement: Topographic information for Tooting crater will also be 

included in the new map, enabling the distribution of geomorphic features seen in 

THEMIS and MOC images to be compared with the MOLA elevation and local slope 

information. This will be particularly important for the analysis of ejecta thickness and 

the geometry of the crater cavity. 
Figure 1 (left): Uncontrolled photomosaic of all the THEMIS VIS and daytime IR images of Tooting 

crater. Even at this scale, it is evident that not all of the ejecta had the same flow properties, as evidenced 

by the blocky nature of the deposit to the east of the rim crest. The white box delineates the area of 

coverage shown in Fig. 2. Figure 2 (right, top and bottom): Preliminary geologic map of the southwestern 

floor and rim of Tooting crater (at bottom right), mapped from THEMIS image V01990003 (at top right). 

Units are as follows: “Cp” – Central peak; “Cf” – hummocky crater floor; “Cm” - melt sheet on crater 

floor; “T” – terraces; “f1” – lobate flows on inner wall, interpreted to be impact melt comparable to that 

seen on the Moon [Hawke and Head, 1977]; “Eh” – hummocky ejecta on outer rim; “Es” – smooth ejecta 

on outer rim; “f2” – lobate flows on exterior rim, interpreted to be impact melt. 

References

 

Hawke, B.R. and J.W. Head (1977). Impact melt on lunar crater rims. In Impact & Explosion Cratering 

(D.J. Roddy, R.O. Pepin and R.B. Merrill, editors), pp. 815 – 841, Pergamon Press, N.Y. 

Howard, K.A. (1975). Geologic Map of the Crater Copernicus. U.S. Geological Survey Map I-840. 

Kieffer, S.W. and C.H. Simonds (1980). The role of volatiles and lithology in the impact cratering 

process. Rev. Geophys. Space Phys. 18: 143 – 181. 

McEwen, A., and 8 others (2005). The rayed crater Zunil and interpretation of small impact craters on 

Mars, Icarus, 176, 351-381. 

Mouginis-Mark, P.J., J.M. Boyce, V.E. Hamilton, F.S. Anderson (2003). A very young, large, impact 

crater on Mars. Int. Mars Conference VI (abstract #3004). 
GEOLOGIC MAPPING RESULTS OF THE OLYMPIA CAVI REGION OF MARS (MTM 85200): UNITS 

AND HISTORY. J. A. Skinner, Jr. and K. Herkenhoff, Astrogeology Team, U.S. Geological Survey, 2255 N. 

Gemini Drive, Flagstaff, AZ 86001 (jskinner@usgs.gov). 

Introduction. The north polar plateau of Mars contains geologic units that record some of the most recently active processes on the surface of the planet [1-3]. 

New, 1:500K-scale geologic mapping of MTM 85200 

provides detailed insight into the units and history of the 

polar plateau, including the evolution of deeply-exposed, 

low albedo basal materials and repetitive deposition and 

planation of the uppermost dust-ice units. 

MTM 85200 includes dunes of Olympia Undae, the 

wide troughs and deep depressions of Olympia Cavi 

(provisional name [pers. comm. J. Blue, USGS]), and the 

narrow, spiral troughs of Boreales Scopuli. A >1000 m 

high sinuous scarp located at ~85° N (herein termed the 

boreal scarp) elevates higher latitude spiral troughs 

above the lower latitude rugged troughs, scarps, and 

dune fields and is a major physiographic and geologic 

feature within the quadrangle. 

Datasets and Methods. Primary base maps included 

(1) the Mars Global Surveyor (MGS)-borne Mars Orbiter Laser Altimeter (MOLA) 231 m/pixel digital elevation model (DEM) and related products, and (2) a Viking Orbiter 2 (VO2) summer 1978 (Ls

 between 134 and 

137) image mosaic. Mars Odyssey-borne Thermal Emission Spectrometer (THEMIS) visual range and Mars 

Express-borne High Resolution Stereo Camera (HRSC) 

image mosaics supplemented the primary map bases. 

Internet hotlinked MGS Mars Orbiter Camera (MOC) 

narrow-angle and THEMIS visual range image footprints provided fundamental access and visualization of 

all available high resolution images. Data were coregistered, rendered, and analyzed using ESRI’s ArcMap 

GIS software package. 

Geologic units. The map units, structure, and symbology represented in our MTM 85200 geologic map represents a concerted effort to correlate (where plausible) the 

results from recently completed [4] and ongoing [5] geologic map efforts and recent topical studies [6-9] of the 

north polar plateau and surrounding regions. We present 

our map units as belonging to the Borealis geologic map 

province, as defined by [4]. Though we observed two 

craters in the polar sequences, their paucity precludes 

crater-age determination; relative ages presented herein 

are postulated based on geological context. 

Olympia Cavi units. The Olympia Cavi dominate the 

polar plateau south of the boreal scarp and include wide 

(>15 km) and deep (>500 m) troughs and depressions. 

We discriminate three geologic units that crop out within 

the Olympia Cavi. The Early Amazonian units form the 

lowest elevation and stratigraphically oldest exposures 

within the map boundary. These units, which form rugged outcrops in southwest-facing trough walls, dip shallowly (<2°, where measurable) to the south. The older of 

these two units (Olympia Cavi 1 unit--ABoc1) consists of 

an upward gradation of massive to thickly-bedded materials with moderate to low albedo. The unit occurs between -4200 and -4800 m elevation and ranges in apparent thickness from ~100 to ~350 m. 

The younger, immediately superposed unit (Olympia 

Cavi 2 unit--ABoc2

) includes thickly-bedded materials 

with low to very low albedo and intercalated, thin, highalbedo layers. Unit ABoc2

 occurs between -4200 and -

4800 m elevation and ranges in apparent thickness from 

~50 to ~300 m. The ABoc1

-ABoc2 contact ranges between -4350 to -4700 m elevation. Some diffuse unconformities separate the units, though in other locations an 

absent or subdued contact may suggest an upward gradation between units. 

The Late Amazonian Olympia Cavi 3 unit (ABoc3) is 

the youngest of the cavi units and drapes unit ABoc1 on 

trough floors and at the base of the pole-facing trough 

walls. The unit is only identified south of the boreal 

scarp. In MOC images, unit materials are exposed in a 

“swirled” pattern that fills shallow depressions within 

underlying units and forms topographically smooth, 

moderate albedo deposits at the base of pole-facing 

trough walls. 

Olympia Undae units. The Olympia Undae extend 

from 120° to 240° E longitude and are comprised of 

dune fields and subjacent materials. We discriminate two 

units within the Olympia Undae. The older unit (Olympia Undae 1 unit--ABou1

) forms a 20-km-wide band between the margins of the polar plateau and the overlying 

erg. The surface of unit ABou1 generally consists of highalbedo, linear swales (300 to 600 m spacing and 10’s of 

meters amplitude) oriented concentric to the polar plateau and perpendicular to the regional wind direction 

[10]. Unit ABou1

 pre-dates the younger layered deposits 

(described below) and may be equivalent in age or older 

than the older layered deposits. 

The younger unit (Olympia Undae 2 unit--ABou2) 

covers unit ABou1 and consists of low-albedo barchan 

dunes, which indicate easterly winds. The unit is also 

mapped near the western margins of the wide troughs 

and depressions of the Olympia Cavi. Dune forms have 

similar low albedo, are spatially associated with, and 

onlap unit ABoc2 suggesting it is a source for the aeolian 

unit. 

Planum Boreum units. The north polar plateau is 

dominated by layered deposits exposed in the uppermost 

sections of Olympia Cavi south of the boreal scarp and 
within the entire south-facing trough walls and floors of 

Boreales Scopuli north of the boreal scarp. We divide 

the layered deposits into two units, roughly equivalent to 

the upper and lower layered deposits described by [9]. 

The Planum Boreum 1 unit (unit ABb1) consists of thick 

(>10 m) beds with multiple, alternating high and low 

albedo layers. The unit erodes into scalloped alcoves, 

particularly at lower latitude and elevation. Angular unconformities are common within unit ABb1, with most 

observed proximal to the boreal scarp and at trough terminations. The Planum Boreum 2 units drape the lower 

layered sequences and are divided into lower and upper 

members. The lower member (Planum Boreum 2a unit--

ABb2a) consists of thin layers positioned above a subtle 

unconformity that is not always present. Layers have 

lobate margins and distinctive alternating high/low and 

speckled albedo patterns. The upper member (Planum 

Boreum 2b unit--ABb2b) is the equivalent of polar ice of 

previous maps (e.g., unit Api of [3]). Our extent is based 

on a VO2 mosaic of images acquired during late Martian 

summer of 1976. We map unit ABb2b as draping (in some 

instances) both Planum Boreum 1 and 2a units. We use a 

buried contact to represent the relationship of the 1976 

ice extent with underlying layered deposits, as observed 

in MOLA, MOC, and THEMIS data. 

Geologic history. During the Early Amazonian, the 

Olympia Cavi 1 and 2 units were emplaced, forming the 

base of the polar plateau and burying volatile-rich materials and mantles of the Vastitas Borealis (VB) units [4]. 

The polar basal units may extend no deeper than ~-4800 

m elevation based on the average elevation of the surrounding VB units. The Olympia Cavi 1 unit was emplaced through the accumulation of fine-grained materials, perhaps related to the erosion of the Scandia region 

materials [9], Chryse outflow sediments, volcanic materials and/or the emplacement of ice-rich surface mantles. 

We interpret the massive to thickly-bedded character of 

these materials to reflect post-emplacement (and perhaps 

repetitive) climate oscillations that desiccated volatilerich strata, resulting in compaction and disruption of 

internal layers. The Olympia Cavi 1 unit was subsequently eroded into irregular mountains and hillocks 

<500 m in height based on unit thickness and the irregular contact with overlying materials. Broad-scale trough 

orientation may date to the Early Amazonian scouring of 

the Olympia Cavi 1 unit. Accumulation of thick, dark 

deposits both against and above eroded Olympia Cavi 1 

unit vestiges formed the Olympia Cavi 2 unit. Geologically recent dune sources from this unit suggest that it is 

made up (in part) of sand-sized material; finer-grained 

material may have accumulated at higher elevations to 

form apparent gradational material boundaries with the 

eroded, underlying Olympia Cavi 1 unit. Both Olympia 

Cavi units were subsequently subjected to aeolian scouring and devolatilization, where disaggregated lithic particles may have been re-distributed into lower latitudes 

as (1) sand sheets through surface saltation and (2) surface mantles through atmospheric fall-out. Though we 

cannot yet discriminate discrete erosional events within 

the mapped sequences, the Olympia Cavi units likely 

represent multiple accumulation-degradation events that 

occurred throughout the Amazonian. Accumulation of 

ice and non-volatile material as both layered deposits 

and migrating sand sheets during periods of low solar 

insolation may have been followed by devolatilization, 

compaction, and erosion during periods of high solar 

insolation. 

During the Late Amazonian, the Olympia Undae 1 

unit was emplaced, perhaps as an early (and since 

planated and partly buried) sequence of layered deposits 

(as suggested by [11]). Alternatively, the unit may postdate the Planum Boreum 1 unit. During the latest major 

decrease in solar insolation (estimated at ~5 Myr [9,12]), 

the Planum Boreum 1 unit was emplaced as thick sequences of dust and ice layers, where unconformities 

record periodic erosion perhaps related to orbital 

changes, volcanic activity at lower latitudes, or other 

causes. These events were of insufficient intensity/longevity to destroy the entire unit. Surface erosion 

may have been concentrated along pre-existing surface 

swales and troughs based on observed angular unconformities at trough terminations. During the most recent 

high obliquity cycle (estimated at ~20 Kyr [9,12]), the 

Planum Boreum 1 unit was severely scoured and quickly 

followed by a resumption of dust-ice deposition to form 

the Planum Boreum 2 units. The latitudinal variation of 

the seasonal frost boundary records alternating periods 

of surface scour and surface deposition, as reflected by 

the overlapping nature of unit ABb2b on underlying upper 

and lower layered deposits. 

Further work. We are finalizing map text and will 

submit the map for review by the end of summer 2006. 

In addition, we have submitted an abstract to the 4th International Conference on Polar Science and Exploration 

(Oct 2-6, 2006) to present the results concerning the 

most recent geologic evolution of MTM 85200 units. 

References. [1] Cutts et al. (1976) Science 194,

1329-1337. [2] Thomas P. et al. (1992) in Mars, pp. 

767-795. [3] Tanaka and Scott (1987) USGS I-1802-C. 

[4] Tanaka et al. (2005) USGS SIM 2888, 1:15M scale. 

[5] Tanaka et al. (2006) LPSC XXXVII abs. # 2344. [6] 

Byrne and Murray (2001) JGR 107, doi:10.1029/ 

2001JE001805. [7] Kolb and Tanaka (2001) Icarus 154, 

22-39. [8] Fishbaugh and Head (2005) Icarus 174, 444-

474. [9] Tanaka (2005) Nature 437, 991-994. [10] Tsoar 

et al. (1979) JGR 84, 8167-8180. [11] Fishbaugh and 

Head (2000) JGR 105, 22,455-22,486. [12]Laskar et al.

(2002) Nature 419, 375-377. 
GEOLOGIC MAPPING AND STRATIGRAPHY OF NORTH POLAR DEPOSITS ON MARS: 

PRELIMINARY RESULTS. K.L. Tanaka1

, K.F. Mullins1, J.A. Skinner, Jr. 1, J.A.P. Rodriguez2, and C.M. Fortezzo1, 3; 1

Astrogeology Team, U.S. Geological Survey, Flagstaff, AZ 86001 (ktanaka@usgs.gov); 2Dept. Earth and 

Planetary Sci., U. Tokyo, Tokyo, Japan; 3

Dept. of Geology, Northern Arizona U., Flagstaff, AZ. 

Introduction: We report on preliminary results of 

detailed photogeologic mapping at 1:5,000,000 scale 

of parts of the north polar region on Mars that expose 

key geologic elements and relationships. Our goal is to 

better understand the interplay of local stratigraphy, 

H2O ice and CO2 frost, climate, and insolation and 

eolian processes in the development and modification 

of north polar stratigraphy and geomorphology. At 

present, extensive data sets for the north polar region 

include a MOLA DEM at 115 m/pixel resolution and 

thousands of THEMIS VIS and IR, HRSC, and MOC 

wide- and narrow-angle images acquired at various 

times. TES and THEMIS data provide useful albedo 

and thermophysical information. 

The Rupes Tenuis unit: Much of the basal part of 

Planum Boreum within and west of Chasma Boreale 

consists of nearly horizontally bedded strata of possibly Early Amazonian age [1] exposed on the floor of 

Chasma Boreale and along and above parts of Rupes 

Tenuis [1]. This prominent scarp runs from the southwest margin of Chasma Boreale westward to ~240o E. 

and rises hundreds to ~1000 m above Vastitas Borealis 

and ~600 m above the floor of Chasma Boreale. We 

name the basal strata of Planum Boreum the Rupes 

Tenuis (RT) unit. 

Along Rupes Tenuis, the RT unit forms most of the 

thickness of Planum Boreum but is partly buried by 

younger layered deposits and mantle material that obscures its morphology (THEMIS V05209008). RT is 

crowned at 287o E. by two massive layers having a 

combined thickness of ~100 m and whose eroded margins include circular to elongate knobs mostly <1 km 

across. The massive layers appear to dip gently westward. Below these, about 20 layers (and/or layer sequences) totaling <850 m can be discriminated in better exposures, but they generally cannot be traced continuously for more than several kilometers. These beds 

appear to have somewhat uneven thicknesses. Locally, 

scarps cut across the beds and may result from faulting. The unit thins westward and cannot be traced with 

certainty west of ~242o E. 

For the Chasma Boreale floor platform, the RT unit 

is reduced to ~10 layers totaling 200 to 350 m in thickness [2]. MOC images (e.g., R2300500 and S0100879) 

indicate minor faulting, tilting, and fracturing and local 

burial by thin layered material. 

None of these better exposures of the RT unit display dunes emanating from them and thus the unit does 

not make up part of the dark platy deposit described as 

forming the base of the Olympia Undae unit below. 

Rather, the RT unit may result from erosion and redeposition of materials generated by mud volcanism 

from the Scandia Tholi, Cavi, and Colles region, covering ~1.5 x 106

 km2 of surrounding plains and averaging ~100 m in thickness [2]. This reworking may have 

involved the adherence of fine-grained particles to 

polar surface ice. Rapid erosion of the RT unit ensued, 

perhaps resulting in much of the present form of the 

deposits. Subsequent stabilization of these deposits 

permitted the accumulation of the presently observed 

Early Amazonian crater population. 

Amazonian craterforms—Implications for paleomantles: Based primarily on MOLA data, >1800 

craterforms have been identified in the northern plains 

characterized by elevated interior floors and highstanding, horizontal to gently sloping, modified ejecta 

blankets [1, 3]. The observed craterforms may be indicative of impact-armored mantle material, which was 

subsequently removed where unarmored, leaving a 

perched (pedestal) crater. The distribution of these 

craterforms throughout the northern plains suggests 

that mantles were often present and in flux following 

formation of the Vastitas Borealis units [1]. Pedestal 

craterforms are also evident on the RT unit where exposed on Planum Boreum, including within Chasma 

Boreale, indicating that thick, Planum Boreumcentered layered deposits like the PB1 unit described 

below have been absent during much of the Amazonian [2]. Here, we refer to these inferred lowland mantles as the Vastitas Borealis paleomantle (VBP) unit. 

The Olympia Undae unit: The dark north polar 

ergs of Olympia, Abalos, and Hyperboreae Undae 

mapped as the Olympia Undae (OU) unit [1] consist of 

dunes tens to hundreds of meters wide of varied form 

and areal coverage. The dunes are generally superposed on a moderately dark surface marked locally by 

fine ripples (>15 m in wavelength; e.g., MOC 

R0100086), which are oriented perpendicular to the 

wind direction indicated by barchan dune orientations. 

Locally, the dark surface includes broader undulations 

~100 to 300 m in wavelength. The dunes emerge from 

beneath layered sequences mapped as Planum Boreum 

unit 1 (PB1) [1] where an uneven dark layer is locally 

detected (e.g., MOC E0201976). The dark layer may 

be buried dune material. The dunes are also partly buried by thin, bright deposits, mapped as the PB2 unit, as 
well as by young mantle deposits. The interdune ripples may be similar in age to the dunes, postdating the 

dark undulating material in places (e.g., MOC 

S0100668). In scalloped depressions along the margin 

of Planum Boreum, the dark material underlying the 

dunes and PB1 unit has a layered, platy appearance [4] 

and is locally buried by patches of possibly PB2 unit 

(e.g., MOC R0100728). Thus the OU unit consists of 

(1) a moderately dark, platy, locally basal member, (2) 

a very dark, uneven, probably sandy member locally 

made up of dunes discontinuously overlying the platy 

member, and (3) dark dunes and less-dark ripples that 

discontinuously overlie the eroded surface of the platy 

unit. The platy and dark members formed after the RT 

and VBP units and prior to PB1 unit. The dark dunes 

may include both exhumed dunes of the dark member 

[5] and younger dunes resulting from erosion of the 

platy and dark members prior to deposition of PB2 and 

mid-latitude mantle (MLM) [6] units. The interdune 

ripples may be made up of a non-saltating sand component. A 19-km-diameter crater provisionally named 

Jojutla at 81.7oN, 190.1oE within Olympia Undae 

likely formed in the midst of the platy unit sequence; 

the ejecta rests on the Olympia lobe and the crater contains some dark platy layers and dunes. 

Formerly, Olympia Undae was interpreted to be 

underlain by PB1-equivalent layered deposits due to 

its domical regional shape [7]. However, we see only 

evidence for the opposite relationship (e.g., MOC 

E0201976). Overall, it may be that each platy layer, 

where not cross-bedded, represents an epoch of sandsea migration and accumulation. These deposits then 

became subdued and modestly indurated during quiescent periods that may have included accumulation of 

icy layered deposits, which are locally observed in 

eroded scarps as bright interlayers (e.g., MOC 

E0201209). The dark upper layer may be the youngest 

of the sand-sea layers, but for some reason did not 

become indurated. The upper dune and ripple member 

is in close spatial association with the platy and dark 

members, indicating that the dunes have not migrated 

significantly since erosion of the PB1 unit and the 

platy and dune members. Also, dunes generally appear 

not to have migrated since emplacement of the PB2 

unit. 

Planum Boreum 1 unit. The lower part of this 

unit locally appears to be dark and may represent lag 

deposits, whereas upper parts appear to include cyclic 

albedo sequences [8]. We observe that the lower dark 

zone begins with darker, thicker beds at the base. We 

suggest that this may be due to inclusion of higher 

proportions of wind-blown fines derived from erosion 

of paleomantles (VDP unit) and materials of the OU 

unit. Ground-penetrating MARSIS radar echoes across 

accumulating ice layers of Planum Boreum east of 

Chasma Boreale suggest low-loss material such as a 

pure, cold ice [9]. This part of the PB units is farthest 

from exposures of the OU unit and thus likely freer 

from reworked OU material. Lower parts of PB1 unit 

include numerous unconformities, which may result in 

part from early episodes of trough insolationcontrolled deepening perhaps associated with eolian 

removal and transfer of dark fines disaggregated from 

dark layers within the unit [10, 11]. 

Planum Boreum 2 unit: This unit consists of several alternating dark and bright layers and rests unconformably over PB1 and OU units and is potentially 

stratigraphically equivalent to the mid-latitude mantle 

(MLM). In troughs of Planum Boreum, it displays a 

basal dark layer that may be preferentially eroded from 

the troughs [10]. The surface of the PB2 unit appears 

rough in MOC images, and locally displays ripples 

similar in appearance to those associated with the OU 

unit (e.g., MOC M0000063). 

Summary: Our north polar stratigraphic results are 

preliminary, and we likely will find additional stratigraphic units and relations with further study. However, some key findings are emerging, including: (1) 

much of Planum Boreum is long-lived, consisting of 

the evenly layered, moderately deformed and cratered, 

and heavily eroded Rupes Tenuis unit; (2) the circumpolar dunes are derived from platy and dark materials 

that underlie layered deposits and appear to form sequences (a) underlying Olympia Undae, (b) surrounding parts of Planum Boreum south of Rupes Tenuis 

and north Olympia Undae, and (c) covering parts of 

the RT unit on the floor and walls of Chasma Boreale; 

(3) the Planum Boreum 2 and MLM units may be 

stratigraphically equivalent; (4) circum-polar dunes 

generally underlie the PB2 and MLM units and thus 

appear to be largely inactive; (5) dark veneers appear 

to be made up of fines eroded from the OU unit and 

dark layers within the PB units; (6) many PB1 unconformities may be due to episodes of trough lengthening; and (7) Chasma Boreale may largely be the result 

of katabatic winds along its northwestern marginal 

scarp, which formed long before the OU and PB units 

were emplaced above it. 

References: [1] Tanaka K.L. et al. (2005) USGS Map I-2888. 

[2] Tanaka K.L. (2005) Nature 437, 991. [3] Skinner J.A., Jr., et al. 

(2005) LPSC XXXVII, Abs. #1476. [4] Byrne S. and Murray B.C. 

(2002) JGR 107, 5044. [5] Mullins K.F. et al. (2005) LPSC XXXVII, 

Abs. #1998. [6] Mustard J.F. et al. (2001) Nature 412, 411. [7] 

Fishbaugh K.E. and Head J.W. III (2000) JGR 105, 22,455. [8] Milkovich S.M. and Head J.W. (2005) JGR 110, doi:10.1029/ 

2004JE002349. [9] Picardi G. et al. (2005) Science. [10] Rodriguez 

J.A.P. et al. (2005) LPSC XXXVII, Abs. #1437. [11] Fortezzo C. and 

Tanaka K.L. (2005) LPSC XXXVII, Abs. #2277. 
GEOLOGIC MAPPING OF THE MEDUSAE FOSSAE FORMATION ON MARS AND THE NORTHERN 

LOWLAND PLAINS OF VENUS. J. R. Zimbelman, CEPS/NASM MRC 315, Smithsonian Institution, 

Washington, D.C., 20013-7012; zimbelmanj@si.edu. 

Introduction: This report summarizes the status 

of mapping projects for both Mars and Venus, 

supported by NASA grant NAG5-11743 (for which a 

no-cost extension ends this year). It is anticipated 

that the three maps discussed below will be submitted 

to the USGS by the end of the year. 

Medusae Fossae Formation (MFF), Mars: 

Mapping in the eastern portion of MFF was initially 

undertaken at 1:500K scale by the PI using the best 

available Viking imaging. However, it soon became 

apparent that this scale was smaller than was 

necessary to portray the geologic relationships 

derived from the images. Mapping was then 

conducted at 1:4M scale, incorporating the results 

obtained from the initial study into a broader regional 

context. As THEMIS daytime IR images became 

available, it soon became apparent that 1:4M scale 

could not adequately portray the rich detail available 

from these new data [1]. Somewhat like Goldilocks, 

we finally settled upon a scale of 1:2M as ‘just right’ 

in order to take advantage of the information in the 

daytime IR THEMIS images while also covering a 

reasonable portion of the planet [2, 3]. This scale 

also corresponds to the USGS series of Viking-based 

photomosaics for Mars. ISIS software made it 

possible to project and mosaic daytime IR THEMIS 

images in order to make a base image for the 

mapping. The coverage of released daytime IR 

images is presently nearly complete within MC 8-SE 

(0° to 15°N lat., 202.5° to 225°E long.), the location 

for which we have produced a geologic map at 1:2M 

scale. The mapping results to date have proved 

helpful in evaluating the history of the global 

dichotomy in the Amazonis region of Mars [4], 

strengthened the case for an ignimbrite origin for 

MFF [5], and in establishing the context for 

evaluating formation mechanisms potentially active 

in western portions of MFF [6]. 

The Gordii Dorsum escarpment is the dominant 

structural and topographic feature within MC 8-SE 

(Figure 1). The daytime IR THEMIS images reveal 

an incredible wealth of detail, due to the combination 

of a uniform dust cover across the region and the 

THEMIS daytime IR sensitivity. The new mapping 

has revealed five distinct subunits for the upper 

member of MFF and three subunits for the middle 

member of MFF. Following USGS convention, the 

coloring of the geologic units is superposed on the 

base image in a way that allows much of the image 

detail to ‘show through’ the color. Unit designations 

follow after those of the global geologic map [7]; 

Figure 1. Portion of geologic map for MC 8-SE, 

centered on the Gordii Dorsum escarpment. Geology 

is superposed on a base of THEMIS daytime IR 

images. Stratigraphy and MOLA cross-sections are 

included below the map. 

these units are identified as Amu1 to Amu5 and 

Amm1 to Amm3 (subscript 1 being the oldest, 

stratigraphically lowest unit), where ‘A’ refers to the 

Amazonian epoch, the first ‘m’ refers to MFF in 

general, ‘u’ refers to the upper (globally defined) 

member of MFF, and the second ‘m’ refers to the 

middle (globally defined) member of MFF. 

The contacts and structures on the map can be 

easily related to MOLA topography, allowing for 

unprecedented assessments of the geology in threedimensions (bottom of Figure 1). There is at present 

no confident way to project the surface contacts to 

the core of a feature as large as the mound associated 

with Gordii Dorsum, so the cross-sections include 

large question marks in their interiors. However, the 

two cross-sections clearly show that the layering 

indicated by the subdivisions of Amu is not uniform 

along the length of Gordii Dorsum. The 

northernmost cross-section (B to B’) has a slight 
easterly dip as compared to the southernmost crosssection (A to A’); a newly identified secondary fault 

is located between the cross-sections and we 

conclude that the faulting is likely related to the 

change in dip. The northernmost section also shows 

a unit exposed on the eastern side of the topographic 

mound (Amu3) that is not evident on the western side 

of the topographic mound; this is strong evidence for 

a significant unconformity within the subunits of 

Amu. 

Northern Lowland Plains, Venus: A 1:5M 

scale geologic map of the Kawelu Planitia (V-16; 25° 

to 50°N lat., 240° to 270°E long.) region of the 

northern lowland plains of Venus has been reviewed 

through the USGS, and is in final preparation for 

resubmission. Substantial revisions to the plains 

stratigraphy took place following the submission of 

the map; Figures 2 and 3 illustrate the V-16 map 

units and their relative stratigraphy, respectively. 

The primary science result derived from the mapping 

is a detailed stratigraphy identified for lava flows 

from several volcanic centers around the Sekmet 

Mons volcano [8], which should be valuable in 

evaluating hypothesized modes of emplacement for 

the plains. Geologic mapping of the Bellona Fossae 

(V-15; 25° to 50°N lat., 210° to 240°E long.) region 

[9] (Figure 4), immediately west of the Kawelu 

Planitia map, has continued in parallel with the 

evolution of the V-16 stratigraphy. Complex 

interfingering of lava flows around Sekmet Mons [8] 

extends into the eastern portion of V-15, but the 

remainder of the quadrangle is relatively simpler than 

that in V-16. The PI was also assigned the Ulfrun 

Regio map (V-27; 0° to 25°N lat., 210° to 240°E 

long.), but it will now be made available for future 

mapping by other researchers. 

Figure 2. Geologic map of V-16 (Kawelu Planitia). 

Figure 3. Stratigraphy of map units in V-16 (Fig. 2). 

Figure 4. Geologic map of V-15 (Bellona Fossae), 

over SAR image base. 

REFERENCES: [1] Zimbelman J.R. et al. (2003) 

LPS 34, Abs. #1390. [2] Shockey K.M. et al. (2004) 

LPS 35, Abs. #1539. [3] Shockey K.M. and 

Zimbelman J.R. (2005) LPS 36, Abs. #1799. [4] 

Irwin R.P. et al. (2004) JGR 109, E09011, 

10.1029/2004JE002248. [5] Zimbelman J.R. (2003) 

GSA Abs. Prog. 35(6), 128. [6] Burr D.M. et al. 

(2006) LPS 37, Abs. #1367. [7] Scott D.H. and 

Tanaka K.L. (1986) USGS Map I-1802-A. [8] 

Zimbelman J.R. (2003) JGR 108, E5, 

10.1029/2002JE001965. [9] Zimbelman J.R. (2004) 

Planetary Geology Mappers Meeting Abstracts, 

ZIMBELMAN2004PGM.PDF, USGS.