**GEOLOGIC MAP**

**OF THE**

**MICHAELANGELO (H-12)**

**QUADRANGLE**

**OF MERCURY**

By

Paul D. Spudis and James G. Prosser

1984

Prepared for the

National Aeronautics and Space Administration

by

U.S. Department of the Interior, U.S. Geological Survey

(Published in hardcopy as USGS Miscellaneous Investigations Series Map
I--1659, as part of the Atlas of Mercury, 1:5,000,000 Geologic Series.
Hardcopy is available for sale from U.S. Geological Survey, Information
Services, Box 25286, Federal Center, Denver, CO 80225)

Please direct questions or comments about the digital version to:

Richard Kozak

U.S. Geological Survey

2255 N. Gemini Drive

Flagstaff, AZ 86001

e-mail: rkozak@flagmail.wr.usgs.gov

**DESCRIPTION OF MAP UNITS**

**PLAINS MATERIALS**

pvs VERY SMOOTH PLAINS MATERIAL---Forms smooth, featureless plains on
floors of c4 and c5 craters (for example, within Bash\\O(o,--), --32°,
170°; FDS 0166846). *Interpretation:* Impact melt sheet and clastic
fallback debris associated with host crater

ps SMOOTH PLAINS MATERIAL---Widespread throughout map area in commonly
contiguous patches May also occur as primary floor material in c4 and c3
craters and as crater-fill material in c3 to c1 craters. Surface planar
to gently undulating. Appears sparsely cratered at Mariner 10
resolutions (FDS 0166837). *Interpretation:* Origin of regional deposits
uncertain, but they most likely consist of volcanic flows analogous to
those of lunar maria. Alternatively, could be associated with ballistic
debris of multiring basins that had a large melt component. Primary
crater-floor deposits probably consist of impact melt and clastic debris
that are slightly more degraded than unit pvs due to greater age

psi NTERMEDIATE PLAINS MATERIAL---Forms planar to undulating surfaces
that have higher crater density than smooth plains material, but are
less heavily cratered than intercrater plains material. May locally fill
floors of c3 to c1 craters. Gradational with smooth plains material in
some places (as at --52°, 137°) and with intercrater plains material in
others (--66°, 142°). *Interpretation:* Probably similar to smooth
plains unit, but older; may consist of volcanic flows or distal ejecta
of multiring basins or possibly a complex mixture of both

pi INTERCRATER PLAINS MATERIAL---Forms extensive, undulating to hummocky
surfaces between areas of large, overlapping craters. In detail,
displays complex topography of coalescing secondary craters. Appears to
predate most map units, but locally may overlie c1 crater rims and
numerous ghost craters. *Interpretation:* Complex unit including crater
and basin deposits and possibly volcanic flows. Probably lithologically
equivalent to lunar highlands megaregolith

**BASIN MATERIALS**

brl BEETHOVEN BASIN RIM MATERIAL---Radially lineated and grooved
material outside rim of Beethoven (basin centered at --20°, 124°).
Extensive to east and southeast of basin; in narrow band directly to
west. Large crater chains (unit csu) aligned with radial texture.
*Interpretation:* Ejecta produced by impact that formed Beethoven.
Radial texture due to ballistic deposition of both melt and clastic
debris. Some lineations may be structural in origin. Exact age
uncertain; density of superposed primary impact craters (table 1)
suggests a post-Caloris, late c3 age, but may be as old as early c2 due
to large range of error in crater age estimate

cvs CALORIS GROUP, VAN EYCK FORMATION, SECONDARY CRATER
FACIES---Overlapping craters larger than 20 km in diameter that appear
to have formed simultaneously; in two clusters near west map border.
Southern cluster (--49°, 182°) superposed on Dostoevskij Basin
materials. *Interpretation:* Secondary impact craters from the Caloris
Basin impact. Form, distribution, and resemblance both to lunar basin
secondaries and to Caloris secondaries outside map area suggest similar
origin

trl TOLSTOJ BASIN RIM MATERIAL---Radially lineated and grooved material
outside rim of Tolstoj (basin centered at --16°, 165°). Extensive south
of basin, but appears embayed by intercrater plains material to
southeast. Large crater chains (unit csu) aligned with radial texture.
*Interpretation:* Ejecta produced by the impact that formed Tolstoj.
Radial texture due to ballistic deposition of melt and clastic debris.
Some lineations may be structural in origin. Density of superposed
primary impact craters (table 1) suggests a pre-Caloris, c2 or c1 age

drl DOSTOEVSKIJ BASIN RIM MATERIAL---Radially lineated and grooved
material outside rim of Dostoevskij (basin centered at --44°,

176°). Extensive north and south of basin, but greatly restricted to
east because of nondeposition or overlap by younger units. Extent of
material to west cannot be determined due to terminator position just
west of basin rim. Large crater chains and clusters (unit csu) aligned
with radial texture. *Interpretation:* Ejecta produced by the impact
that formed Dostoevskij. Radial texture due to ballistic deposition of
melt and clastic debris. Some lineations may be structural in origin,
particularly in the area at --40°, 174°, where the Dostoevskij rim
intersects a ring of the preexisting Barma-Vincente Basin. Density of
superposed primary impact craters (table 1) suggests a pre-Caloris, c1
age

m MASSIF MATERIAL---Forms generally isolated, equant to rectilinear
massifs that protrude through adjacent units. Type area: --50°, 174°;
FDS 0166843. *Interpretation:* Fragments of rings from nearly
obliterated multiring basins Barma-Vincente, Hawthorne- Riemenschneider
and Eitoku-Milton. Probably consist of brecciated autochthonous rocks
and melt rocks produced by the basin impact. Used in conjunction with
arcuate ridge segments and scarps to delineate basin rings

**CRATER MATERIALS**

> CRATER MATERIALS---Craters ≥30 km in diameter. *Interpretation:*
> Impact crater materials of various degrees of degradation and
> infilling. Rate of degradation may be accelerated by adjacent impact
> events; therefore, stratigraphic significance of morphology is only
> approximate. Morphologic classification based on system of N. J. Trask
> (McCauley and others, 1981)

c5 Material of craters with very fresh rim crest, terraces, radial
texture, rays, and few or no superposed craters---Floor-wall contact
very sharp. Floored by very smooth plains material (example:
Bash\\O(o,--), --32°, 170°)

cp5 Central-peak material---May consist of single peak, elongated peak,
or peak dusters (a function of increasing crater size).
*Interpretation:* Uplifted, brecciated autochthonous rocks formed
contemporaneously with host crater

cr5 Radially textured material and secondary crater field forming
annulus outside some c5 craters

cs5 Satellitic-crater materials forming secondary crater clusters and
chains---Host crater identified; associated with c5 craters

c4 Material of craters with continuous, slightly subdued rim crest---Few
superposed craters; generally no rays visible. Floor-wall contact sharp.
Floor consists mostly of very smooth or smooth plains materials
(example: Hawthorne, --51°,116°)

cp4 Central-peak material---May consist of single peak, elongated peak,
peak clusters, or peak rings (a function of increasing crater size).
*Interpretation:* Uplifted, brecciated autochthonous rocks formed
contemporaneously with host crater

cf4 Crater-floor material---Hummocky, rough-textured material forming
floor deposits in some c4 craters; usually embayed by plains material

cr4 Radially textured material and secondary crater field forming
annulus outside unit c4---Shown only for craters \>100 km in diameter

cs4 Satellitic-crater materials forming secondary crater clusters and
chains---Host crater identified; associated with c4 craters

c3 Material of craters with rounded but continuous rims---Flat floors
generally filled with smooth plains or intermediate plains materials.
Central peaks uncommon except in basins such as Michelangelo. Moderate
number of superposed craters (example: Barma (Yakovlev), --41°, 163°)

cp3 Central-peak material---May consist of single peak, elongated peak,
peak clusters, or peak rings (a function of increasing crater size).
*Interpretation:* Uplifted, brecciated autochthonous rocks formed
contemporaneously with host crater

cf3 Crater-floor material---Hummocky, rough-textured material forming
floor deposits in some c3 craters; usually embayed by plains material

cr3 Radially textured material and secondary crater field forming
annulus outside c3 craters---shown only for craters \>100 km in diameter

cs3 Satellitic-crater materials forming secondary crater clusters and
chains---Host crater identified; associated with c3 craters

c2 Material of craters with rounded, subdued rims and flat
floors---Floor may be filled with either smooth plains or intermediate
plains materials. No radial texture evident in exterior deposits. Many
superposed craters (example: Sei, --64°, 90°)

cp2 Central-peak material---Very rare single peak. *Interpretation:*
Uplifted, brecciated autochthonous rocks formed contemporaneously with
host crater

c1 Material of flat-floored craters with low, discontinuous rim
crests--- No radially textured ejecta; no preservation of secondaries.
Floor is filled with smooth plains or intermediate plains materials and
is filled locally by ejecta blankets from adjacent craters. Large number
of superposed craters (example: Milton, --26°,175°)

csu Satellitic crater material, undivided---Occurs as crater pairs,
clusters, or chains that are satellitic to a larger host crater or
basin. Location of host feature mostly uncertain. *Interpretation:*
Secondary impact craters formed by ballistic erosion of subjacent
terrain

> CONTACT---Queried where doubtful; dotted where buried
>
> SCARP---Probably a fault. Bar and ball on downthrown side
>
> RIDGE---Interpreted as mare-type wrinkle ridge within smooth plains
> and intermediate plains materials; probably of compressive tectonic
> origin. Symbol on ridge crest
>
> RIDGE SCARP---Associated with rupes structures; probably of
> compressive tectonic origin. Line marks base of slope; barb points
> downslope
>
> DEPRESSION OF PROBABLE STRUCTURAL ORIGIN, LINEAR TO ARCUATE---Barbs
> point downslope
>
> CRATER RIM CREST
>
> CRATER RIM CREST, SUBDUED---Either degraded by age (c1 and c2 craters)
> or buried by later unit
>
> IRREGULAR DEPRESSION---Possibly a collapse crater
>
> BASIN RING CREST---Interpreted as part of basin ring of structural
> origin
>
> MULTIRING BASIN RING---Subdued ring of large multiring basins
> Barma-Vincente, Bartok-Ives, Hawthorne-Riemenschneider, and
> Eitoku-Milton. Solid line indicates mappable structural or topographic
> element; dots indicate inferred ring position
>
> AREA OF BRIGHT CRATER-RAY MATERIAL---Interpreted as fresh crater
> ejecta
>
> AREA OF ABNORMALLY LOW ALBEDO

**INTRODUCTION**

The Michelangelo quadrangle is in the southern hemisphere of Mercury,
where the imaged part is heavily cratered terrain that has been strongly
influenced by the presence of multiring basins. At least four such
basins, now nearly obliterated, have largely controlled the distribution
of plains materials and structural trends in the map area. Many craters,
interpreted to be of impact origin, display a spectrum of modification
styles and degradation states. The interaction between basins, craters,
and plains in this quadrangle provides important clues to geologic
processes that have formed the morphology of the mercurian surface.

Several low-albedo features are evident in Earth-based views of the
Michelangelo quadrangle (Davies and others, 1978, p. 15), but these
features do not appear to correlate directly with any mapped terrain
unit. Solitudo Promethei may correspond to a deposit of plains materials
centered at --58°, 135°, and Solitudo Martis may correspond to similar
materials at --30° to --40°, 90° to 100°. The color data
(orange/ultraviolet) presented in Hapke and others (1980) likewise show
no particular correlation with mapped terrain types. The "yellow" region
(moderately high orange/ultraviolet) centered at --33°, 155° appears to
correspond to a smooth plains deposit, but the region overlaps into
adjacent cratered terrain.

Mariner l0 data include complete photographic coverage of the quadrangle
at a resolution of about 2 km. In addition, twelve stereopairs cover
scattered areas in the quadrangle (Davies and others, 1978, p.
114--115); these photographs were used to supplement the geologic
interpretation. About 10° of longitude of the H-13 quadrangle (Solitudo
Persephones Province) adjacent to the west is included in the map area
because not enough Mariner 10 data were acquired of this quadrangle to
justify the production of another map.

**STRATIGRAPHY**

**ANCIENT BASIN MATERIALS**

Systematic mapping of the Michelangelo quadrangle has revealed the
presence of four nearly obliterated multiring basins These basins are
here named for unrelated superposed, named craters, as was done for
highly degraded lunar basins (Wilhelms and El-Baz, 1977). From oldest to
youngest, the basins are: Barma-Vincente, centered at --52°, 162°;
Bartok-Ives, centered at --33°, 115°; Hawthorne-Riemenschneider,
centered at --56°, 105°; and Eitoku-Milton, centered at --23°, 170°.
Diameters of the basin rings are given in table 1. The presence of these
basins is indicated by three criteria: (1) isolated massifs (unit m)
that appear to protrude through superposed materials; (2) arcuate
segments of ridges (rupes) aligned with massif material; and (3) arcuate
scarps aligned with both massifs and ridges.

Because none of the four basins has ejecta deposits that are preserved,
the basins are assumed to be the oldest features in the map area;
moreover, they are embayed or buried by all other units. The relative
ages of the basins are given in table 1, based on the density of
superposed primary impact craters and stratigraphic relations. These
results are uncertain, as the crater density of heavily cratered terrain
on Mercury ranges from 11.2 to 17.4 x 10-5 km-2 for craters of diameters
20 km or greater (Guest and Gault, 1976). The results obtained are
consistent with a qualitative assignment of relative age that is based
on position and size of these ancient basins.

The basins have largely controlled subsequent geologic processes in the
map area. Large concentrations of smooth plains deposits are found
within the basin boundaries and at the intersections of rings of
different basins. Moreover, the trends of scarp segments, interpreted by
some workers to be expressions of thrust faults associated with global
compression (Strom and others, 1975; Dzurisin, 1978), are deflected into
basin-concentric patterns at their intersection with basin rings. These
relations have also been noted for ancient basins on both the Moon
(Schultz, 1976) and Mars (Schultz and others, 1982; Chicarro and others,
1983).

In addition to the four multiring basins, an ancient two-ring basin,
Surikov, is also evident at --37°, 125°. It is unique among the two-ring
basins in the map area because, although the inner ring is well
preserved and similar in morphology to peak rings of fresh basins such
as Bach, the outer ring is almost totally obliterated. This morphology
is similar to that of the lunar basin Grimaldi and is suggestive of an
extended period of structural rejuvenation along the margins of the
inner ring. Crater density on this basin suggests that it is one of the
oldest in the map area (table 1).

**OLDER PLAINS MATERIALS**

The oldest recognizable plains unit in the map area is the intercrater
plains material (unit pi), originally described by Trask and Guest
(1975). This material is generally undulating to hummocky and appears to
underlie tracts of cratered terrain, as evidenced by the superposition
of many coalescing secondaries from adjacent large craters. In some
areas, the intercrater plains material appears to embay c1 craters, and
it is found in all of the degraded basins described above. The origin of
mercurian intercrater plains material remains unknown. Both volcanic
(Strom and others, 1975; Trask and Guest, 1975; Strom, 1977) and
impact-debris models (Wilhelms, 1976a; Oberbeck and others, 1977) have
been proposed. The material is most likely polygenetic, including both
crater and basin debris and possibly ancient volcanic flows. Physically
and lithologically it resembles the lunar highlands megaregolith.

**YOUNGER BASIN MATERIALS**

At least seven basins in or partly in the Michelangelo quadrangle
postdate or are contemporaneous with the last stages of deposition of
intercrater plains material. Dostoevskij (--44°, 176°) displays only one
ring; presumably the inner peak ring is buried by plaint material. The
ejecta from this basin (unit drl) may be mapped as far as 450 km from
the rim; several secondary crater chains occur southeast of the rim.
Although Dostoevskij was considered a type example of a c3 large crater
(McCauley and others, 1981), crater counts indicate that it is much
older (table 1). The Dostoevskij impact probably occurred in cl time.

The Tolstoj Basin is centered in the Tolstoj quadrangle at --16°,165°
(Schaber and McCauley, 1980). It consists of three discontinuous rings
(table 1); ejecta (unit trl) may be mapped as far as 350 km from the
outermost ring. The density of superposed craters suggests an age older
than the Caloris Basin, either late c1 or early c2. A small. unnamed
basin at --48°, 136° may also have formed in this time interval (table
1), but its age is uncertain due to its partial burial by ejecta from
crater Delacroix (--44°, 129°).

The effects of the Caloris impact on the map area are not immediately
apparent. No Caloris ejecta are evident, and most structural trends
appear to be unrelated to this impact. However, near the west border of
the map are two groups of large, overlapping craters centered at --31°,
183° and --49°, 182°. These groups appear to have formed simultaneously,
as no specific stratigraphic sequence is evident. On the basis of crater
clusters of similar appearance in the lunar highlands, which have been
interpreted as Imbrium and Orientale basin secondaries (Schultz, 1976;
Wilhelms, 1976b; Eggleton, 1981), these crater groups are interpreted to
be Caloris Basin secondaries. Following the terminology developed by
McCauley and others (1981) we have assigned them to the Van Eyck
Formation, Secondary-Crater Facies (unit cvs). These secondaries overlie
Dostoevskij ejecta and thus confirm that basin as pre-Caloris. We
determined a reference crater density for Caloris in the Shakespeare
quadrangle (table l) in order to correlate basin ages to that
stratigraphic datum.

The Beethoven Basin (--20°,124°), partly exposed in the Michelangelo
quadrangle, consists of one ring 660 km in diameter. The exact age of
Beethoven is uncertain; the density of superposed primary impact craters
(table 1) suggests a post-Caloris, late c3 age, but it may be as old as
early c2 age due to the large range of error in the crater age estimate.
The ejecta from Beethoven (unit brl) are very extensive east and
southeast of the basin rim and are mappable as far as 600 km downrange
from the rim. However, ejecta appear to be almost absent on the west
side of the basin. The reason for this asymmetry is unclear; possibly
Beethoven is the result of an oblique impact that produced an asymmetric
ejecta distribution (Gault and Wedekind, 1978), or possibly basin radial
texture in the western rim area has been obliterated by ejecta from
V\\O(a,--)lmiki.

The other basins in the quadrangle are Michelangelo, V\\O(a,--)lmiki,
and Bach (table 1). All contain two rings and appear to be transitional
between large craters and multiring basins. All postdate the Caloris
event.

**YOUNGER PLAINS MATERIALS**

The oldest of the three younger plains units is intermediate plains
material (unit psi). It forms planar to gently undulating surfaces and
both embays tracts of cratered terrain and fills crater floors. Both
upper and lower contacts with other plains units are gradational. These
gradations suggest that the assignment of age to plains deposits on
Mercury is partly dependent on the relative abundance of superposed
secondary craters, whose densities vary widely as a function of nearby
source craters.

The smooth plains unit (ps) forms both widespread regional deposits and
crater floor material. The regional deposits are significantly less
cratered than those of other plains units, although they typically
display crater densities comparable to older lunar maria (Murray and
others, 1974). The unit characteristically contains mare-type ridges,
although no flow fronts have been observed in the map area.

The origin of the younger plains materials is critical to mercurian
geologic history. They are thought to be either volcanic (Strom and
others, 1975; Trask and Strom, 1976) or a facies of ballistic ejecta
(Wilhelms, 1976a; Oberbeck and others, 1977). The interpretation favored
here is that large parts of these smooth plains are of volcanic origin,
because (1) they are distributed regionally and have no obvious source
for ballistic deposition; (2) large tracts are confined within basin
depositional environments, analogous to the lunar maria; (3) indirect
evidence elsewhere on Mercury exists for volcanic modification of impact
craters (Schultz, 1977); and (4) possible volcanic collapse craters are
associated with plains-filled craters (--61°, 161° and --57°, 102°).
Parts of smooth plains deposits may be a complex mix of overlapping
crater ejecta.

A very smooth plains unit (unit pvs) occurs only as floor material in
younger c4 and c5 craters. The material is interpreted to be crater
impact melt and associated clastic debris.

**CRATER MATERIALS**

Crater deposits are mapped stratigraphically according to a morphologic
degradation sequence devised by N. J. Trask (McCauley and others, 1981).
This method assumes that (1) all craters of a given size range initially
resemble fresh craters and (2) degrees of impact erosion are constant
for all craters within a morphologically defined sequence. Although
these conditions hold generally, degradation may be accelerated locally
by adjacent impact events and flooding by plains materials and, rarely,
may be decelerated by structural rejuvenation of topographic elements of
craters. Thus, the stratigraphic significance of crater morphology is
only approximate. By analogy with lunar materials, all mapped crater
materials are thought to be of impact origin. Only craters larger than
30 km in diameter are mapped.

The large basins of the Michelangelo quadrangle have been dated
relatively by counting the cumulative density of superposed primary
impact craters that have diameters greater than 20 km (table 1). This
technique has proven to be of great value in dating lunar basins
(Wilhelms, in press), where obvious superposition relations do not
exist. Results of these crater counts indicate that Dostoevskij,
presumed to be of c3 age (McCauley and others, 1981), is actually one of
the oldest basins in the map area (early c1). Thus, strict morphological
determination of stratigraphic age may be significantly in error.

Throughout the map area are crater clusters and chains (unit csu) that
are satellitic to both craters and basins, but the host crater may not
be identifiable everywhere. This material is interpreted to be from
secondary impact craters of a wide variety of ages. Many mercurian
secondaries are well preserved and have sharp, unrounded rims. This
morphology is probably a consequence of the stronger mercurian gravity,
relative to the Moon. that produces higher impact velocities for crater
ejecta on the mercurian surface (Gault and others, 1975; Scott, 1977).

**STRUCTURE**

The rings associated with the four ancient basins (table 1) are the
oldest structures within the mapped area and have to some degree
controlled the structural trends of subsequent tectonism. Several of the
lobate ridges described by Strom (1979) follow arcuate patterns along
rings of the Barma-Vincente Basin; Hero Rupes is an example. These
lobate ridges appear to be of compressive tectonic origin and, although
global in distribution, may be deflected locally by the presence

of preexisting, basin-related structure. Additional effects of these
ancient basin rings may be seen where the rim of Dostoevskij intersects
the Barma-Vincente rings (for example, the horst at --40°, 174°); parts
of the Dostoevskij rim appear to have been structurally accented by this
intersection. These relations are similar to those associated with
highly degraded, ancient basins on Mars (Chicarro and others, 1983). The
smooth plains material (unit ps) displays numerous ridges that generally
resemble lunar mare ridges and also are considered to be of tectonic
origin. The mercurian ridges are probably related to minor compressive
stresses that postdate smooth plains emplacement. Numerous lineaments
are associated with basin rim material (units drl, trl, brl), but most
of these lineaments are probably related to ejecta deposition. A few may
be faults, particularly where they occur close to preexisting basin
rings.

**GEOLOGIC HISTORY**

The interpretable geologic history of the Michelangelo quadrangle begins
with the formation of the four ancient, multiring basins. From oldest to
youngest, they are: Barma-Vincente, Bartok-Ives,
Hawthorne-Riemenschneider, and Eitoku-Milton. These basins presumably
formed during the period of heavy bombardment inferred from lunar
history (Wilhelms, in press). Contemporaneous with their formation and
shortly afterward, was the deposition of the intercrater plains
material. This unit has a complex history of deposition; it was reworked
in place and probably includes brecciated plutonic rocks and possibly
ancient volcanic flows. Deposition of the intercrater plains material
was waning as the next oldest basins (Dostoevskij, Tolstoj) were formed.
Partly overlapping their formation was the deposition of the
intermediate plains material, probably emplaced partly as distal basin
ejecta and partly as volcanic flows. Regional deformation of these
plains units by compressive tectonics, forming scarps, was
contemporaneous with there deposition.

The Caloris impact occurred during the time of formation of the
intermediate plains material. In the map area, Caloris ejecta may be
present at depth or may have been reworked locally by adjacent impacts.
Two groups of Caloris secondary craters (unit cvs) are evident. Shortly
after the Caloris impact, extensive smooth plains material, probably of
volcanic origin, was deposited. During this period of deposition
occurred the impacts of the last of the major basins (Beethoven,
Michelangelo, V\\O(a,--)lmiki, and Bach). Minor tectonic activity
continued as scarps and lunar mare-type wrinkle ridges developed within
the smooth plains materials.

The cratering rate declined rapidly as the c3, c4 and c5 craters were
produced. Regolith production continues to the present day on all units.
If the geologic history of the Moon is a guide, most of the events
discussed were essentially complete within the first 1.5 to 2.0 billion
years of Mercury's history (Murray and others, 1975). A summary of
global mercurian geology may be found in Guest and O'Donnell (1977) and
Strom (1979).

**REFERENCES CITED**

Chicarro, Augustin, Schultz, P. H., and Masson, Philippe, 1983, Basin
control of ridge patterns on Mars: Abstracts of papers submitted to the
Lunar and Planetary Science Conference, 14th, Houston, 1983, p.
105--106.

Davies, M. E., Dwornik, S. E., Gault, D. E., and Strom, R. G., 1978,
Atlas of Mercury: National Aeronautics and Space Administration Special
Publication SP-423, 128 p.

Dzurisin, Daniel, 1978, The tectonic and volcanic history of Mercury as
inferred from studies of scarps, ridges, troughs, and other lineaments:
Journal of Geophysical Research, v. 83, no. B10, p. 4883--4906.

Eggleton, R. E., 1981, Map of the impact geology of the Imbrium basin of
the Moon, *in* Geology of the Apollo 16 area---Central Lunar Highlands:
U.S. Geological Survey Professional Paper 1048, pl. 12.

Gault, D. E., Guest, J. E., Murray, J. B., Dzurisin, Daniel, and Malin,
M. C., 1975, Some comparisons of impact craters on Mercury and the Moon:
Journal of Geophysical Research, v. 80, no. 17, p. 2444--2460.

Gault, D. E., and Wedekind, J. A., 1978, Experimental studies of oblique
impact: Lunar and Planetary Science Conference, 9th, Houston, 1978,
Proceedings, v. 3, p. 3843--3875.

Guest, J. E., and Gault, D. E., 1976, Crater populations in the early
history of Mercury: Geophysical Research Letters, v. 3, no. 3, p.
121--123.

Guest, J. E., and O'Donnell, W. P., 1977, Surface history of Mercury: A
review: Vistas in Astronomy, v. 20, p. 273--300.

Hapke, Bruce, Christman, Craig, Rava, Barry, and Mosher, Joel, 1980, A
color-ratio map of Mercury: Lunar and Planetary Science Conference,
11th, Houston, 1980, Proceedings, v. 1, p. 817--821.

McCauley, J. F., Guest, J. E., Schaber, G. G., Trask, N. J., and
Greeley, Ronald, 1981, Stratigraphy of the Caloris Basin, Mercury:
Icarus, v. 47, no. 2, p. 184--202.

Murray, B. C., Belton, M. J. S., Danielson, G. E., Davies, M. E., Gault,
D. E., Hapke, Bruce, O'Leary, Brian, Strom, R. G., Suomi, Verner, and
Trask, N. J., 1974, Mercury's surface: Preliminary description and
interpretation from Mariner 10 pictures: Science, v. 185, no. 4146, p.
169--179.

Murray, B. C., Strom, R. G., Trask, N. J., and Gault, D. E., 1975,
Surface history of Mercury: Implications for terrestrial planets:
Journal of Geophysical Research, v. 80, no. 17, p. 2508--2514.

Oberbeck, V. R., Quaide, W. L., Arvidson, R. E., and Aggarwal, H. R.,
1977, Comparative studies of lunar, martian, and mercurian craters and
plains: Journal of Geophysical Research, v. 82, no. 11, p. 1681--1698.

Schaber, G. G., and McCauley, J.F., 1980, Geologic map of the Tolstoj
quadrangle of Mercury: U.S. Geological Survey Miscellaneous
Investigations Series Map I-1199, scale 1:5,000,000.

Schultz, P. H., 1976, Moon morphology: Austin, Tex., University of Texas
Press, 626 p.

\_\_\_\_\_\_1977, Endogenic modification of impact craters on Mercury:
Physics of the Earth and Planetary Interiors, v. 15, nos. 2--3, p.
202--219.

Schultz, P. H, Schultz, R. A., and Rogers, John, 1982, The structure and
evolution of ancient impact basins on Mars: Journal of Geophysical
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Scott, D. H., 1977, Moon-Mercury: Relative preservation states of
secondary craters: Physics of the Earth and Planetary Interiors, v. 15,
nos. 2--3, p. 173--178.

Strom, R. G., 1977, Origin and relative age of lunar and mercurian
intercrater plains: Physics of the Earth and Planetary Interiors, v. 15,
nos. 2--3, p. 156--172.

\_\_\_\_\_\_1979, Mercury: A post-Mariner 10 assessment: Space Science
Reviews, v. 24, p. 3--70.

Strom, R. G., Trask, N. J., and Guest, J. E., 1975, Tectonism and
volcanism on Mercury: Journal of Geophysical Research, v. 80, no. 17, p.
2478--2507.

Trask, N. J., and Guest, J. E., 1975, Preliminary geologic terrain map
of Mercury: Journal of Geophysical Research, v. 80, no. 17, p.
2461--2477.

Trask, N. J., and Strom, R. G., 1976, Additional evidence of mercurian
volcanism: Icarus, v. 28, no. 4, p. 559--563.

Wilhelms, D. E., 1976a, Mercurian volcanism questioned: Icarus, v. 28,
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\_\_\_\_\_\_1976b, Secondary impact craters of lunar basins: Lunar
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Map I-948, scale 1:5,000,000

> **NOTES ON BASE**
>
> This map sheet is one of a series covering that part of the surface of
> Mercury that was illuminated during the Mariner 10 encounters (Davies
> and Batson, 1975). The source of map data was the Mariner 10
> television experiment (Murray, 1975).
>
> ADOPTED FIGURE
>
> The map projections are based on a sphere with a radius of 2,439 km.
>
> PROJECTION
>
> The Lambert conformal conic projection is used for this sheet, with a
> scale of 1:4,623,000 at lat --22.5°. Latitudes are based on the
> assumption that the spin axis of Mercury is perpendicular to the plane
> of the orbit. Longitudes are positive westward in accordance with the
> usage of the International Astronomical Union (IAU, 1971). Meridians
> are numbered so that a reference crater named Hun Kal (lat --0.6°) is
> centered on long 20° (Murray and others, 1974; Davies and Batson,
> 1975).
>
> CONTROL
>
> Planimetric control is provided by photogrammetric triangulation using
> Mariner 10 pictures (Davies and Batson, 1975). Discrepancies between
> images in the base mosaic and computed control-point positions appear
> to be less than 5 km. The base mosaic was tied to a much later
> iteration than the base mosaics of other Mercury quadrangles.
> Discrepancies as large as 20 km were adjusted along the north edge to
> match the Tolstoj (H-8) and Beethoven (H-7) quadrangles. No attempt
> was made to join the Discovery (H-11) quadrangle to the east or the
> Bach (H-15) quadrangle to the south. Discrepancies as large as 40 km
> exist on these boundaries.
>
> MAPPING TECHNIQUES
>
> Mapping techniques are similar to those described by Batson (1973a,
> b). A mosaic was made with pictures that had been digitally
> transformed to the Lambert conformal conic projection. Shaded relief
> was copied from the mosaics and portrayed with uniform illumination
> with the sun to the west. Many Mariner 10 pictures besides those in
> the base mosaic were examined to improve the portrayal. The shading is
> not generalized and may be interpreted with nearly photographic
> reliability (Inge, 1972; Inge and Bridges, 1976).
>
> Shaded relief analysis and representation were made by P. M. Bridges.
>
> NOMENCLATURE
>
> All names on this sheet are approved by the International Astronomical
> Union (IAU, 1977, 1980).
>
> H-12: Abbreviation for Mercury (Hermes) sheet number 12.
>
> H 5M --45/135 G: Abbreviation for Mercury (Hermes) 1:5,000,000 series;
> center of sheet, lat --45°, long 135°; geologic map, G.
>
> A small part of the H-13 quadrangle is included on this sheet because
> insufficient data are available to justify preparation of a separate
> sheet.
>
> REFERENCES CITED
>
> Batson, R. M., 1973a, Cartographjc products from the Mariner 9
> mission: Journal of Geophysical Research, v. 78, no. 20, p.
> 4424--4435.
>
> \_\_\_\_\_1973b, Television cartography: U.S. Geological Survey
> Open-File Report, Astrogeology 58, 35 p.
>
> Davies, M. E., and Batson, R. M., 1975, Surface coordinates and
> cartography of Mercury: Journal of Geophysical Research, v. 80, no.
> 17, p. 2417--2430.
>
> Inge, J. L., 1972, Principles of lunar illustration: Aeronautical
> Chart and Information Center Reference Publication RP-72-1, 60 p.
>
> Inge, J. L., and Bridges, P. M., 1976, Applied photointerpretation for
> airbrush cartography: Photogrammetric Engineering and Remote Sensing,
> v. 42, no. 6, p. 749--760.
>
> International Astronomical Union, 1971, Commission 16: Physical study
> of planets and satellites, *in* 14th General Assembly, Brighton, 1970,
> Proceedings: International Astronomical Union Transactions, v. 14B, p.
> 128.
>
> \_\_\_\_\_1977, Working Group for Planetary System Nomenclature, *in*
> 16th General Assembly, Grenoble, 1976, Proceedings: International
> Astronomical Union Transactions, v. 16 B, p. 330--333, 351--355.
>
> \_\_\_\_\_1980, Working Group for Planetary System Nomenclature, in
> 17th General Assembly, Montreal, 1979, Proceedings: International
> Astronomical Union Transactions, v. 17B, p. 291 .
>
> Murray, B. C., 1975, The Mariner 10 pictures of Mercury---an overview:
> Journal of Geophysical Research, v. 80, no. 17, p. 2342--2344.

Murray, B. C., Belton, M. J. S., Danielson, G. E., Davies, M. E., Gault,
D. E., Hapke, Bruce O'Leary, Brian, Strom, R. G., Soumi, Verner and
Trask, Newell, 1974, Mercury's surface: Preliminary description and
interpretation from Mariner 10 pictures: Science, v. 185, no. 4146, p.
169--179.