Chryse trough Chryse trough

Valles Marineris Valles Marineris

Margaritifer Chaos Margaritifer Chaos

Margaritifer Margaritifer

basin

Noachis Noachis

basin

Paraná

basin

Ladon basin Ladon basin

Holden

basin

Jones

volcano volcano

Newcomb Newcomb

Holden

MARGARITIFER M A R G A R I T I F E R

TERRA 

Uzboi

Valles

Himera V Himera Valles

Paraná

Valles

Ladon

Valles

Samara

Loire

Morava

Valles

Valles

Valles

–20012

–25012

HNp

HNp

HNp

HNp

AHct

HNvn

HNvn HNvn

HNvn

HNvn

B

Paraná 

basin 

8A

13A

10

11A

9

Novara

Loire Valles Loire Valles

Paraná

Valles

Erythraeum Chaos Erythraeum Chaos

7

AHct 12

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Erythraeum Chaos

Novara

Paraná Valles

Paraná Valles

Valles 

Loire 

c3

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Npld

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c1

ANb

AHe

AHp

HNp

AHvn

AHf

AHmw

HNf

HNvn

AHct

AHe

AHp

AHe AHp

AHp

AHf

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c3

Npld

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AHvn

AHvn

AHvn

AHvn

Npld

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AHct

AHp AHct

AHe

AHmw AHf AHvn

HNf HNvn

AHct

AHe

ANb

AHp

c2

c1

c3

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Jones2

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AHp

AHp

AHp

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HNp

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HNp

HNp

HNp

HNp

AHvn

AHvn

c2

HNvn

AHvn

AHvn

HNf

HNf

HNf

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

AHmw

HNvn

Npld

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

HNvn

AHp

AHf

AHct

AHct

AHct

AHct

AHct

AHct

AHct

AHct

AHct

AHct

AHct

AHe

AHe

AHe

AHe

AHe

AHe

ANb

ANb

ANb

ANb

ANb

ANb

ANb

ANb ANb

ANb

c1

c1

c3

c3

c3

c3

c3

c3

c3

c3

c3

c3

c3

c3

c3

c3

c3

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c3

c3

c3

c3

c2

c3

c3

c3

c2

c3

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c3

c3

c3

c3

c3

c3

c1 c3

Npld

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Npld

Npld

Nm

Nm

Nm

c1

AHct

AHe

AHct

HNvn

HNvn HNvn

HNvn

HNf HNf

HNf

HNf

15°

10°

14° 13° 12° 11°

–19°

–18°

–20°

–21°

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15° 14° 13° 12° 11° 10°

–18°

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–26°

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20 0

–10°

325° 330° 335° 340° 345° 360°

–15°

–20°

–25°

20 40 60 80 100

SCALE 1:1 004 000 (1 mm = 1.004 km ) AT 350° LONGITUDE

TRANSVERSE MERCATOR PROJECTION

Prepared for the

National Aeronautics and Space Administration

Prepared on behalf of the Planetary Geology and 

Geophysics Program, Solar System Exploration 

Division, Office of Space Science, National Aeronautics 

and Space Administration

Edited by Jan L. Zigler; cartography by Darlene A. Ryan

Manuscript approved for publication July 18, 2008

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, 

Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Available at http://pubs.usgs.gov/sim/3041

Geologic Map of MTM –20012 and –25012 Quadrangles, Margaritifer Terra Region of Mars

By

J.A. Grant1, S.A. Wilson1, C.M. Fortezzo2, and D.A. Clark3

2009

Scientific Investigations Map 3041

Atlas Of Mars: MTM –20012 and –25012 Quadrangles

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey

Printed on recycled paper

1Center for Earth and Planetary Studies, Smithsonian Institution,

 Washington, D.C.

2U.S. Geological Survey, Flagstaff, AZ

3Randolph-Macon College, Ashland, VA

Mass

Wasting

Material

Chaotic

Terrain

Material

Crater

Material

System

N(5) age1 AMAZONIAN NOACHIAN HESPERIAN

CORRELATION OF MAP UNITS

Vallis

Material

Highland

Material

Plains

Material

1,000

300

100

30

10

3,000

1Neukum and Hiller (1981)

2Crater Jones located 300 km west of map area

DESCRIPTION OF MAP UNITS

[Unit descriptions and interpretations are based on morphology, texture, albedo, and stratigraphic position as observed in Viking 

Orbiter, Mars Global Surveyor Mars Orbiter Camera (MOC), Odyssey THEMIS, and Mars Reconnaissance Orbiter HiRISE Images. 

THEMIS visible (VIS) image identification numbers, for example V14817005, are used to locate images (table 1, fig. 5)]

MASS-WASTING MATERIAL

Mass-wasting material (Amazonian to Hesperian)—Degraded, isolated tongue of material that 

originates in an alcove on a steep crater wall and extends onto the crater floor (V14817005). Overlies 

bright plains material (unit ANb). Type locality: lat 24.5° S., long 345.18° E. Interpretation: Failure of 

steep wall-rock material emplaced in a mass-wasting event. Unit is younger than bright plains material 

(unit ANb), but degraded appearance is inconsistent with very recent activity

VALLIS MATERIAL

Younger fan material (Middle Amazonian to Late Hesperian)—Forms a smooth to variably rough, 

sometimes light-toned, locally lobe-shaped deposit on the floor of an unnamed crater south of 

Erythraeum Chaos. Deposits incise and bury older fan deposits (unit HNf); channels and depositional 

lobes exhibit fairly uniform, intermediate brightness temperature in THEMIS nighttime IR data. Type 

locality: lat 23.5° S., long 347.7° E. Interpretation: Alluvial fans and associated distal alluvium 

composed of relatively coarse alluvium and (or) partially lithified material deposited on older alluvium 

(unit HNf). Depositional lobes radiating from mouth of younger inlet valley (unit AHvn) lack steep 

fronts, suggesting much of the discharge was subaerial and perhaps deposited as debris flows. 

Preserved lobes indicate episodic flow contemporaneous with associated younger valleys; limited 

evidence of flow from crater suggests ponding was likely and deposits may extend across crater floor 

and beyond lobes

Younger valley network material (Middle Amazonian to Late Hesperian)—Deposits within generally 

isolated, narrow valleys. Few examples found in and south of Erythraeum Chaos where valleys appear 

to incise plains materials (units HNp, AHp). Valleys are generally narrow and sharply defined relative 

to older valleys (unit HNvn) with abrupt headward terminations; no evidence of incised channels or 

developed tributaries. Valleys sometimes entirely confined within younger plains materials, but 

examples incising segments of older valleys and (or) emerging from broader and apparently older 

materials occur within map area (for example, lat 23.7° S., long 348.0° E.). Accumulations of lighttoned, eolian drift exhibit low brightness temperature in THEMIS nighttime IR. Type locality: lat 

20.93° S., long 348.24° E. Interpretation: Sedimentary materials eroded from surrounding plains and 

uplands and deposited by water flowing through poorly integrated valleys. Valley morphometry 

suggests a groundwater source for discharge, perhaps in association with emplacement of younger 

plains materials and (or) final drawdown of regional aquifers. Limited slope/colluvial processes likely 

contributed to greater valley widening and extension

Older fan material (Hesperian to Late Noachian)—Forms a smooth to variably rough, locally elevated, 

fan-shaped deposit(s) and associated materials mantling floors of two unnamed craters. Multiple 

channels and depositional lobes preserved in some cases; deposits exhibit fairly uniform, 

intermediate-brightness temperature in THEMIS nighttime IR data. Surface gradients of fans vary 

(V18199004). Underlies younger fan unit (AHf) in one location (lat 23.5° S., long 347.75° E.). Type 

localities: lat 23.5° S., long 347.9° E.; lat 24.8° S., long 345.1° E. Interpretation: Alluvial fans, deltas, 

and associated alluvium consisting of relatively coarse alluvium and (or) partially lithified material 

deposited on crater floors. Steep fronts suggest some material may have been deposited in crater-lake 

settings. Preserved lobes and distributary channels indicate sustained or perhaps episodic flow, 

probably contemporaneous with period of widespread valley formation (unit HNvn)

Older valley network material (Hesperian to Late Noachian)—Generally smooth and widely distributed 

deposits that fill numerous valleys throughout map area. Valleys often well integrated with preserved 

first- and second-order tributaries; valley floors do not typically exhibit preserved, incised channel 

features and low- to high-brightness temperatures in THEMIS nighttime IR data. Proximal reaches of 

Loire Valles exhibit a highly dissected, crenulated morphology. Type localities: Paraná and Loire Valles 

(for example, lat 22.35° S., long 348.9° E.; lat 21.15° S., long 345.62° E.). Interpretation: Sedimentary 

materials of perhaps varying composition and (or) mineralogy, eroded from surrounding plains and 

uplands and deposited by water flowing through multi-digitate, parallel to dendritic valley networks. 

Valley floors exhibit uneven accumulations of eolian drift and dunes. Small valleys likely formed by 

fluvial processes related to precipitation-recharged groundwater sapping. Crenulated morphology 

likely caused when discharge from Erythraeum Chaos caused down-cutting and headward erosion of 

the main branch of Loire Valles and associated tributaries

CHAOTIC TERRAIN MATERIAL

Chaotic terrain material (Middle Amazonian to Hesperian)—Closely spaced, rounded to flat, elongate 

plateaus, buttes, knobs, and linear ridges, typically separated by troughs. Troughs between plateaus 

have an approximate east-west orientation but are occasionally interrupted by troughs with a northsouth orientation. Plateau surfaces generally smooth at scales of tens to hundreds of meters; most 

appear stripped and expose more resistant material and low, narrow, linear, intersecting ridges. Plateau 

surfaces exhibit intermediate- to high-brightness temperatures in THEMIS nighttime infrared (IR) data, 

whereas intervening troughs are intermediate to dark. Height relative to adjacent troughs ranges from 

tens of meters (north and east of Erythraeum Chaos, for example, lat 18.7° S., long 349.2° E.) to 

100–200 m in Erythraeum Chaos and as much as ~275 m (for example, lat 23.7° S., long 346.7° E.). 

AHct sometimes occurs in depressions bounded along their margins by discontinuous troughs on the 

order of 50–100 m deep and 3-7 km wide (for example, Erythraeum Chaos), whereas in other 

locations, material rises above the level of surrounding plains (for example, lat 23.7° S., long 346.7° 

E.). Wrinkle ridges occur locally and are oriented roughly north-south. Variably embays and cuts 

adjacent younger plains materials (units AHp, AHe, ANb), consistent with crater statistics (N5 age of 

~100). Type locality: Erythraeum Chaos (for example, lat 22° S., long 348.5° E.). Interpretation: 

Remnants of possibly more resistant alluvial (ice-rich?) deposits emplaced in association with older 

vallis materials (unit HNvn) and subsequently modified and exposed by eolian and (or) alternate 

processes. Collapse played a minimal role in formation, whereas some locations rising above level of 

surrounding plains may have experienced substantial constructional contributions via accumulation and 

upward expansion of ice, sedimentary diapirism, or mud volcanism. Expression of wrinkle ridges 

requires some internal strength that may reflect persistence of volatiles in what may be sedimentologically varied alluvium. Local intersecting ridges may reflect small, relatively resistant dikes exposed via 

differential erosion of the surface. Stratigraphic relations indicate a younger age than bulk of valley 

network materials (units HNvn, AHvn) and may be younger than younger plains materials (units AHp, 

AHe, ANb). Origin of dikes may be sedimentary or diagenetic, but proximity of valleys and paucity of 

volcanic landforms argues against a volcanic origin

PLAINS MATERIAL

Etched plains material (Late Amazonian to Late Hesperian)—Local scabby to rough, knobby, pitted 

materials; express relatively high, local relief. Deposits occur along margins of chaotic terrain materials 

(unit AHct) in Erythraeum Chaos; surrounded by younger plains materials (unit AHp). Exhibit 

intermediate brightness temperature in THEMIS nighttime IR data. Margins occasionally lobate. Type 

locality: lat 22.4° S., long 348° E. Interpretation: Possible volatile-rich flow deposits similar in origin 

to chaotic terrain materials, but intermediate strength between younger plains and chaotic terrain materials due to intermediate volatile content. Differential welding and subsequent eolian stripping possibly 

responsible for etched appearance

Bright plains material (Amazonian to Noachian)—Rough to locally knobby material on crater floors. 

Exhibits high-temperature brightness in THEMIS nighttime IR data. Few, degraded impact craters 

preserved. Type locality: Novara crater. Interpretation: Coarse-grained or indurated/cemented, 

fine-grained materials. Possibly bedrock-impact-melt deposits exposed by surface deflation and 

stripping of superposing deposits. Rough texture, composition, knobby appearance, and occurrence of 

few, well-developed valleys within some of the associated craters suggests material is not alluvial in 

origin, and general paucity of volcanic terrains in map region argues against a volcanic origin

Younger plains material (Early Amazonian to Hesperian)—Forms a widespread, lightly cratered plains 

surface; typically embays vallis materials (unit HNvn), older plains materials (unit HNp), mountainous 

material (unit Nm), and dissected unit of the plateau sequence (unit Npld). Occasionally embays 

chaotic terrain materials (unit AHct). Typically confined to topographic lows and basins, except where 

partially encircling chaotic terrain materials in Erythraeum Chaos. North-trending wrinkle ridges, 

partially buried craters (for example, lat 21.4° S., long 346.7° E.), and relatively few incised valleys 

preserved. Generally characterized by intermediate-brightness temperatures in THEMIS nighttime IR 

data. Type locality: lat 21° S., long 347.5° E. Interpretation: Sedimentary and (or) volcanic materials 

partially filling Erythraeum Chaos and burying other surfaces. Often surrounded by younger etched 

(AHe) or older plains (HNp) materials. If sedimentary in origin, location relative to older plains material suggests possible accumulations of locally eroded and redistributed older plains material. Paucity 

of incised valleys relative to surface area implies limited, primary alluvial contributions; general 

absence of volcanic edifices in map area argues against volcanic origin. May be expression of volatilerich, partially welded eolian deposits or impact materials in some locations

Older plains material (Early Hesperian to Late Noachian)—Forms a widespread, relatively low-relief, 

lightly cratered plains surface, often dissected by valley network material. Locally embayed by 

younger plains materials; mantles floors of some moderately degraded craters. Generally north-southoriented wrinkle ridges and buried to partially buried/exhumed craters preserved. Topographically 

lower than older, exposed dissected unit of the plateau sequence (unit Npld) and mountainous material 

(unit Nm). Relatively older than valles materials and deposits (units HNf, HNvn), chaotic terrain material (unit AHct), and younger plains material (unit AHp). Type localities: lat 26.3° S., long 347.5° E. 

Interpretation: Mixture of fluvial/alluvial deposits, colluvium, and volcanic and (or) impact debris, 

which mantle topographic lows in dissected unit of the plateau sequence (unit Npld)

PLATEAU AND HIGHLAND MATERIAL

Dissected unit of the plateau sequence (Early to Middle Noachian)—Widespread, heavily cratered 

surface dissected by small valley networks (not mapped individually) and troughs. Wrinkle ridges and 

scarps are present; generally moderate, locally high-relief surface. Type locality: lat 19.5° S., lat 347.5° 

E. Interpretation: Materials formed during period of high-impact flux and are likely a mixture of lava 

flows, pyroclastic material, and impact breccia (Greeley and Guest, 1987; Scott and Tanaka, 1988)

Mountainous material (Early Noachian)—Topographically high, rugged, and isolated blocks. Type locality: lat 19.5° S., long 349° E. Interpretation: Ancient, resistant crustal material uplifted during formation of impact basins (Greeley and Guest, 1987)

CRATER MATERIAL

[Impact craters with rim diameters <2 km not mapped]

Well-preserved crater material—Characterized by pronounced, continuous crater rims elevated relative to 

surrounding materials, superposed on all surfaces. Well-defined, continuous ejecta blankets are often 

present. Type locality: lat 18.4° S., long 347.87° E. Interpretation: Pristine crater material exhibiting 

little degradation; some crater floors may contain deposits emplaced by mass-wasting, eolian, and (or) 

fluvial processes

Moderately degraded crater material—Characterized by mostly complex craters (>15 km and exhibiting 

terraces, central peaks/rings, and (or) flat floors; see Melosh, 1989) possessing subdued crater rims 

exhibiting minor relief relative to surrounding materials. Crater floors are typically infilled; some crater 

floors contain chaotic terrain (unit AHct). Partially buried or deflated ejecta blankets occasionally 

present. Type locality: lat 18.8° S., long 345.5° E. Interpretation: Impact craters with moderate degree 

of degradation; most crater floors contain deposits emplaced by mass-wasting, eolian, and (or) fluvial 

processes

Highly degraded crater material—Characterized by a degraded, incomplete crater rim that exhibits little 

relief relative to the surrounding materials, a featureless crater floor, and lack of ejecta. Type locality: 

lat 20.5° S., long 347.7° E. Interpretation: Highly degraded impact crater material. Ejecta has been 

completely eroded or mantled by younger materials; rim has been heavily modified by erosion

SYMBOL EXPLANATION

Contact—Dashed where approximately located or gradational. Internal contact distinguishes impact 

features

Fault—Bar and ball on downthrown block

Wrinkle ridge—Line delineates ridge crest

Scarp—Line marks top of slope; hachures point downslope

Small valley

Channel

Radial grooves in ejecta (schematic)

Crater rim—Showing crest where preserved and defined. Hachures point into crater

Buried or exhumed crater

Figure 1. Image showing Margaritifer Terra, within lat 10°–25° S., and long 325°–350° E., which has been 

greatly modified by fluvial and other geomorphic processes and preserves one of the highest drainage densities of valley networks on Mars. Margaritifer Terra is roughly bisected by the north-south-oriented depression 

informally called the "Chryse trough" (approximate axis of the Chryse trough indicated by the dashed yellow 

line), which extends northward from the Argyre impact basin, south of the figure, to the northern plains. 

Paraná-Loire (PL) and Samara-Himera Valles (SH) drain the east side of the Chryse trough, whereas the 

Uzboi-Ladon-Morava (ULM) outflow system drains the west side of the trough. The confluence of these 

drainage systems occurs at the Margaritifer basin near a possible Amazonian-aged volcano. The map area 

divided into MTM –20012 and –25012 quadrangles (lat 17.5°–27.5° S., long 345°–350° E.) is outlined in 

black. Image is a display of Mars Orbiter Laser Altimeter (MOLA) topographic data (64 pixels/degree or 926 

m/pixel) draped over a portion of the Viking MDIM mosaic. North towards top of image.

350° 355°

–4,000 2,000 METERS –2,000 0

–17.5°

–22.5°

–27.5°

345° 350°

AMAZONIAN NOACHIAN HESPERIAN

30

HNf

AHct

AHp

c3 c2 c1

HNp

Npld

Nm

HNvn

10

?

?

?

?

?

?

?

AHf

?

?

300

100

3,000

1,000

Cumulative Number of Craters > 5 km per 106 km2

1Neukum and Hiller (1981)

AHvn

Figure 6. Summary chart of crater statistics compiled by Grant (1987) for surfaces in MTM 

–20012 and –25012 quadrangles, Mars (red dots) and adjacent regional surfaces (black dots). 

The average (red dot) and standard deviation (red line) for counts completed in the map area 

are indicated to the right of unit data. Vertical dashed black lines represent inferred ages of 

various vallis materials and are based on crosscutting and embayment relations with plains 

materials. The uncertainty associated with relative ages for counts within the map area is 

indicated by question marks. Relative ages inferred for mapped local and more regional 

surfaces are similar and imply that events distinguished within the map area affected regional 

surfaces as well. Relative ages were derived from the number of craters >5 km in diameter 

normalized to 106 km2 and based on comparison to the standard curve published by Neukum 

and Hiller (1981). Comparison with alternate standard curves (Hartmann and Neukum, 

2001) yields broadly similar results.

Figure 11. Images showing detail of Paraná Valles in MTM –20012 and –25012 quadrangles, 

Mars. (A) The largest exposure of chaotic terrain material (unit AHct) is located in Paraná basin 

(see fig. 2 for map location). The north edge of the chaotic terrain material is bound by discontinuous troughs along its margin (white arrows). The head of Loire Valles is located on the west margin 

of the chaos material (black arrow). The white ouline shows the location of figure 11B; black 

oulines show the approximate location of figures 8B and 12. MOLA topography (463 m/pixel) over 

a portion of the Mars Viking MDIM 2.1 mosaic (~231 m/pixel). North to top of image. (B) The 

chaotic terrain is characterized by knobs, linear ridges, and buttes that are separated by narrow 

troughs and irregular depressions. The trough along the margin of the chaotic unit in Paraná basin 

(white arrows) is generally 50–100 m deep and 3–7 km wide. Large, discontinuous plateaus in the 

midst of the chaotic terrain suggest resistant capping material in some locations (black arrow). 

Subframe of THEMIS VIS images V18461004, V02298003, V10474003, and V06405002. North 

towards top of image.

Figure 2. Image showing MOLA topography (463 m/pixel) over a 

portion of the Mars Viking MDIM 2.1 mosaic (~231 m/pixel) used 

as the base map for MTM –20012 and –25012 quadrangles (see fig. 

1 for regional setting). MOLA data was used to determine elevation 

relations between mapped landforms and surfaces. The elevation 

within the map area ranges from roughly –3,100 m to over 1,400 m. 

A complete description of the MOLA data set can be found in Smith 

and others (1999). Features in the map area, including Loire Valles, 

Paraná Valles, Paraná basin, and Novara crater are labeled for 

reference. White outlines show approximate locations of figures 7, 

8A, 9, 10, 11A, and 13A. Simple cylindrical projection. North 

towards top of image.

Figure 5. Image showing location of THEMIS Visible (VIS) images in red 

(resolution of ~18 m/pixel) and Mars Orbiter Camera (MOC) narrow angle 

(NA) images in blue (generally <10 m/pixel) within MTM –20012 and 

–25012 quadrangles, Mars (see fig. 1 for regional setting; use location 

numbers to find image numbers in table 1). Images locally reveal increased 

detail that helps to define the morphology and limits of various surfaces within 

the map area. Simple cylindrical projection. North towards top of image. 

THEMIS VIS and MOC images released June 2007.

Figure 7 (left). Image of Loire Valles, west of the outlet from 

Paraná basin (see fig. 2 for map location), composed of valley 

network materials (unit HNvn) that were fed by numerous 

small tributary valleys. Most of the surrounding terrain is older 

plains materials (unit HNp). The deeply incised stem valley in 

the proximal reach of Loire Valles (white arrows) drains toward 

the northwest from Paraná basin. Numerous tributaries in the 

area impart a crenulated appearance to the surface. These 

tributaries likely incised as the trunk valley downcut in 

response to discharge from Paraná basin, enabling adjustments 

toward a more regional base level downstream and an overall 

widened valley form (boundary shown by black arrows). 

MOLA topography (463 m/pixel) over a subframe of the Mars 

Viking MDIM 2.1 mosaic (~231 m/pixel). North towards top of 

image.

–3,140 4,136 METERS

–1160 –520 METERS

0

0 50 km at –20° latitude

0

–1470 –770 METERS

–17.5°

–22.5°

–27.5°

345° 350°

92

101

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A B 0 20 KILOMETERS 0 5 KILOMETERS

–17.5°

–22.5°

–27.5°

345° 350°

0

Figure 3. Subframe of global Thermal Emission Imaging System 

(THEMIS) daytime infrared image mosaic (http://themis.asu.edu) 

covering MTM –20012 and –25012 quadrangles, Mars (~230 

m/pixel resolution; see fig. 1 for regional setting). Solid black 

swaths indicate gaps in data coverage. Simple cylindrical projection. 

North towards top of image.

–17.5°

–22.5°

–27.5°

345° 350°

0 50 KILOMETERS at –20° latitude

Figure 4. Subframe of global Thermal Emission Imaging System 

(THEMIS) nighttime infrared mosaic (http://themis.asu.edu) covering MTM –20012 and –25012 quadrangles, Mars (~230 m/pixel 

resolution; see fig. 1 for regional setting). Some of the plains materials within large crater (unit ANb) display relatively higher nighttime 

brightness temperatures, whereas some of the valley network (unit 

HNvn) floors have lower brightness temperatures (see map text for 

discussion). Solid white swaths indicate gaps in data coverage. 

Simple cylindrical projection. North towards top of image.

0 0 500 METERS

Figure 8. Images showing detail of Paraná Valles in MTM –20012 

and –25012 quadrangles, Mars. (A) The valleys (unit HNvn) that 

make up multidigitate, parallel to dendritic valley networks in 

Paraná and Loire Valles are highly degraded. Very few channels on 

the valley floors are preserved in the map area, but a muted channel 

is distinguishable on the floor of a valley in Paraná Valles (arrows). 

Subframe of THEMIS VIS image V06742003 near lat 20.48° S., 

long 349.49° E. in Paraná Valles (see fig. 2 for map location). North 

to top of image. (B) Most valley floors in the map area are typically 

covered with light-toned, eolian ridges. Subframe of MOC image 

E1302176 near lat 21.92° S., long 348.53° E. in Paraná Valles (see 

fig. 11A for location). North towards top of image.

A B

0 500 METERS

Figure 9. Enlarged image showing stripped, scabby, 

and light-toned nature of the bright plains materials 

(unit ANb) that occurs on the floors of some large 

craters (see fig. 2 for map location) in MTM –20012 

and –25012 quadrangles, Mars. Unit ANb exhibits 

very high brightness temperatures in the THEMIS 

nighttime data (fig. 4), which is consistent with exposures of bedrock. Sparse valleys and the lack of nearby 

volcanic structures suggests the materials are exposed 

impact melts rather than alluvial, volcanic, or eolian in 

origin. The few craters present on the bright plains 

surfaces are highly modified and preclude the determination of a relative age, which suggests they are 

relatively young. Subframe of MOC R0200723 from 

crater floor located at lat 26.6° S., long 349o E. North 

towards top of image.

Figure 10. Image showing fan material (units HNf, AHf) on the 

floor of an unnamed 30-km-diameter crater south of Paraná basin 

(see fig. 2 for map location) in MTM –20012 and –25012 quadrangles, Mars. Multiple channels (dashed lines) and depositional 

lobes (solid lines) are preserved on the surface of the deposits. The 

elevated, oblong portion of the alluvial deposit (HNf, covering ~165 

km2) underlies a younger, sometimes light-toned fan material (unit 

AHf) in the center of the crater. Rugged knobs associated with this 

deposit may be remnants from the crater’s central peak. An outlet 

breach in the northwest rim was primarily incised during the older 

fan (unit HNf) activity and only slightly modified during later activity. Few deposits outside of the crater outlet can be assigned to the 

younger fan (unit AHf). Subframes of THEMIS VIS images 

V16614006, V16302005 and V1960005. North towards top of 

image.

0 5 KILOMETERS

0 500 METERS

Figure 12 (left). Image showing detail of 

Paraná Valles in MTM –20012 and –25012 

quadrangles, Mars. Plateaus in the chaotic 

terrain materials (unit AHct) appear 

stripped and exhibit narrow, crisscrossing 

dikes (arrows) that consist of apparently 

more resistant materials. These dikes could 

mark locations where limited water moving 

through fractures in the material resulted in 

alteration and local diagenesis. Many 

troughs within the chaos materials, such as 

the trough near top of image (~140 m deep 

relative to surrounding plateaus), are 

commonly partially filled with light-toned 

eolian materials. Subframe of MOC NA 

image M0900897 (see fig. 11A for 

location). North towards top of image.

0 500 METERS

Figure 13. Image showing detail along Paraná Valles in MTM –20012 and –25012 quadrangles, Mars. (A) The etched plains material (unit AHe) occurs in patches between the 

margins of the chaotic terrain materials (unit AHct) in Paraná basin and the adjacent 

younger plains materials (unit AHp). The etched plains material exhibits dark-toned, somewhat flat mesas and pits exposing light-toned material. Black outline shows location of 

figure 13B. THEMIS VIS image V17837005 (see fig. 2 for map location). North to top of 

image. (B) Detail of the pitted, scabby, and knobby texture of the etched plains material 

(unit AHe) showing a range of dark- and light-toned materials. Light-toned eolian ridges 

are common throughout the unit. This complex topography, exposed by eolian stripping of 

the surface, is consistent with the juxtaposition of materials in alluvial depositional 

settings. The material may contain (or have contained) less ice than adjacent chaotic terrain 

materials (unit AHct), thereby leading to differential stripping rather than formation of 

additional chaos. Subframe of MOC NA E1500848. North towards top of image.

0 2 KILOMETERS

A B

13B

Chaotic

Terrain

Material

Crater

Material

System

N(5) age1

Vallis

Material

Highland

Material

Plains

Material

20 KILOMETERS

50 KILOMETERS at –20° latitude

2 KILOMETERS

exit breach to

Paraná basin

345° Descriptions of nomenclature used on map are 

listed at http://planetarynames.wr.usgs.gov/

346° 347° 348° 349° 350°

–27.5°

–27.5°

–27°

–26°

–25°

–24°

–21°

–20°

–19°

–18°

–17.5°

–23°

–22°

–27°

–26°

–25°

–24°

–23°

–22°

–20°

–21°

–19°

–18°

–17.5°

KILOMETERS

Planetocentric latitude and east longitude coordinate system shown in black.

Planetographic latitude and west longitude coordinate system shown in red.

345° 346° 347° 348° 349° 350°

MC–19

MC–3

MC–4 MC–5

MC–6

MC–10 MC–11 MC–12 MC–13

MC–1

MC–18 MC–20 MC–21

MC–25

MC–26 MC–27

MC–28

MC–30

QUADRANGLE LOCATION

Photomosaic showing location of map area. An outline of 

1:5,000,000-scale quadrangles is provided for reference.

300°

300°

60°

60°

0°

30°

65°

270° 315° 0° 45° 90°

–30°

–65°

0°

30°

65°

–30°

–65°

North

South

East

West

50 KILOMETERS at –20° latitude

knobby material

light-toned material