**GEOLOGIC MAP**

**OF THE**

**BEETHOVEN (H-7)**

**QUADRANGLE**

**OF MERCURY**

By

John S. King and David H. Scott

1990

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--2048, 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**

\[Cumulative crater counts (Nc) made for craters ≥5 km in diameter per
square kilometer shown for some map units\]

PLAINS MATERIALS

ps **Smooth plains material**---Occurs within c4 and older craters,
locally within low intercrater areas. Craters of c5 age superposed.
Surface smooth, flat; sparsely cratered with few ridges. Nc=7.8 X 10-5 ±
4.5 X 10--5. *Interpretation:* Volcanic and impact melt materials;
clastic ejecta from primary and secondary craters

psi **Intermediate plains material**---Forms relatively smooth, slightly
hummocky surfaces within large intercrater areas and in floors of c3 and
older craters. More densely cratered than smooth plains unit. Nc = 1.1 X
10-4 ± 3.1 X 10-5. Mapped as cratered plains material to east in Kuiper
quadrangle (De Hon and others, 1981). *Interpretation:* Same as for
smooth plains material but older; deposited over larger areas

pi **Intercrater plains material**---Forms rough, planar, highly
cratered surface over western part of map area; grades eastward into
plains and terra material, undivided. Embays and buries parts of
Beethoven basin rim material (unit brl) in places, but in others is
overlapped by the rim material. Nc = 2.3 X 10-4 ± 4.4 X10-5.
*Interpretation:* Crater and basin ejecta, volcanic flows, possible
pyroclastic deposits; many partly buried crater rims contribute to
surface roughness

ptu **Plains and terra material, undivided**---Continuation of same unit
from Kuiper quadrangle (De Hon and others, 1981) to east; mapped there
and in eastern half of Beethoven quadrangle where high sun angle
prevents good image quality. Transitional westward with intercrater
plains material. Surface appears generally flat, highly cratered, with
lobate scarps and broad ridges. Nc = 2.3 X 10-4 ± 3.8 X 10-5.
*Interpretation:* Similar to intercrater plains material and to some
intermediate plains material

BASIN MATERIALS

\[Basins are interpreted to have been formed by impact\]

brl **Beethoven basin rim material**---Radially lineated and grooved
ejecta blanket covering rim of Beethoven basin and extending generally
outward from it; extensive on north and east sides. Craters of c2 and
younger age superposed; abundant clusters of secondary craters 10 to 20
km across. Nc = 1.6 X 10-4 ± 3.8 X 10-5

rrl **Raphael basin rim material**---Extends outward from rim of Raphael
basin. Similar to Beethoven rim material; abundant clusters of craters
10 to 15 km across. Nc=1.1 X 10-4 ± 3.0 X 10-5

CRATER MATERIALS

\[Craters are divided on the basis of their morphologic characteristics
into five categories (c1, oldest, to c5, youngest), which reflect their
degradational state and, ideally, their relative age (McCauley and
others, 1981). Craters less than about 30 km in diameter are not mapped,
excepting rayed craters of c5 age. Rim, wall, and floor materials are
generally not mapped separately, but rim-crest symbol divides exterior
and interior crater deposits. All craters are interpreted to have been
formed by impact\]

c5 **Material of very fresh craters**---Forms floor, rim, and wall of
fresh- appearing, sharp-rimmed, rayed craters. Highest albedo in map
area; haloes and rays may extend many crater diameters from rim crests.
Superposed on all other map units. Generally smaller and fewer than
older craters. Elsewhere on Mercury where sun angle is lower, some

larger, very fresh appearing craters have been mapped as c5, but in this
quadrangle craters of this type cannot be separated from c4 craters

c4 **Material of fresh but slightly modified craters**---Similar in
morphology to c5 craters but without bright haloes or rays; sharp rim
crests; continuous ejecta blankets; very few superposed secondary
craters (unit cs). Floors consist of crater or smooth plains materials

c3 **Material of modified craters**---Rim crest continuous but slightly
rounded and subdued. Ejecta blanket generally less extensive than those
of younger craters of similar size. Superposed craters and rays common;
smooth plains and intermediate plains materials cover floors of many
craters. Central peaks more common than in c4 craters, probably because
of larger average size of c3 craters

cf3 **Floor material of c3 craters**---Hummocky, rough-textured material
forming floor deposits in crater V![](media/image1.pct){width="0.125in"
height="0.18055555555555555in"}lmiki (lat 23° S., long 142°)

cr3 **Rim material of c3 craters**---Forms rough blanket around crater
V![](media/image1.pct){width="0.125in"
height="0.18055555555555555in"}lmiki and crater Haydn in Discovery
quadrangle (Trask and Dzurisin, 1984) adjacent to southeast. Superposed
crater chains mapped as secondary crater material, undivided

c2 **Material of subdued craters**---Low-rimmed, relatively shallow
craters, many with discontinuous rim crests. Floors covered by smooth
plains and intermediate plains materials. Includes rim material of
Raphael basin and several double-ring craters. Crater density of ejecta
blankets similar to that of intermediate plains material: Nc = 1.1 X
10-4 ± 3.0 X 10-5 (Raphael basin rim material); Nc = 1.3 X 10-4 ± 4.3 X
10-5 (Mark Twain ejecta blanket, lat 11° S., long 138°)

c1 **Material of degraded craters**---Similar to c2 crater material but
more deteriorated; many superposed craters

cp **Central peak or ring material**---Occurs in c2 to c4 craters as
single hills or partial rings rising above crater floors near their
centers. *Interpretation:* Precrater brecciated rocks uplifted and
deformed at time of impact

cs **Secondary crater material, undivided**---Occurs throughout
quadrangle as aligned chains of craters of unknown age. Those mapped
probably originate from moderate- to large-size craters within and
outside quadrangle. In places parent or source crater can be inferred by
radial alignment of one or more chains to crater center

> **Contact**---Dashed where poorly defined
>
> **Fault or graben**---Ball on downthrown side
>
> **Scarp**---Line marks base; barb points downslope
>
> **Ridge**---Symbol on ridge crest
>
> **Trough**---Barbs point downslope
>
> **Crater rim crest**
>
> **Crater rim crest**---Greatly subdued or buried
>
> **Crestline of Beethoven basin**
>
> **Bright ray or halo material around or emanating from c5
> craters**---Interpreted as fresh ejecta
>
> **Area of abnormally low albedo**

**INTRODUCTION**

The Beethoven quadrangle is located in the equatorial region of Mercury,
in the center of the imaged area. Most pictures of the quadrangle were
obtained at high sun angles as the Mariner 10 spacecraft receded from
the planet. Geologic map units are described and classified on the basis
of morphology, texture, and albedo, and they are assigned relative ages
based on stratigraphic relations and on visual comparisons of the
density of superposed craters. Crater ages are established by relative
freshness of appearance, as indicated by topographic sharpness of their
rim crests and degree of preservation of interior and exterior features
such as crater floors, walls, and ejecta aprons. Generally, topography
appears highly subdued because of the sun angle, and boundaries between
map units are not clearly defined.

Impact craters larger than about 250 km are referred to as basins.
Unlike many basins on the Moon, however, the two obvious basins in the
quadrangle, Beethoven (610 km in diameter) and Raphael (320 km in
diameter), are not multiringed, whereas well-developed rings encircle
many craters of lesser diameters (Trask, 1976). Remnant ejecta blankets
around parts of the Beethoven and Raphael basins are subdued in
appearance and their margins poorly defined in places. However, where
they can be recognized, these extensive aprons allow a generalized
regional stratigraphic sequence to be determined. A third basin,
extremely subdued but probable, is centered at lat 0°, long 130°.

Images in the northeastern part of the quadrangle are very poor to
unusable. This area therefore contains blank patches or only a few
crater outlines and mapped materials. Another difficulty in mapping is
the poor match in topographic bases between Beethoven and adjacent
quadrangles. Mismatches are especially common along the borders with the
Kuiper and Discovery quadrangles to the east and southeast.

**STRATIGRAPHY**

PLAINS MATERIALS

Major divisions of rock units in the quadrangle are (1) plains materials
and (2) crater and basin materials. Surfaces of the plains units range
in morphology from relatively level but rough to nearly flat and smooth;
the latter terrain has intermediate albedo like that of the Cayley
Formation or older maria on the Moon. Plains materials are identified in
part by surface texture and their relative ages determined by density of
superposed craters. Intercrater plains material (unit pi), one of the
two oldest plains units, was originally described by Trask and Guest
(1975). It covers large areas in the western, central, and southeastern
parts of the quadrangle. There, as in other regions of Mercury (Malin,
1976), its surface reveals the outlines of many buried crater rim crests
and knobby remnants of an older resurfaced terra. This unit has been
scoured by many secondary craters that have formed overlapping chains
and troughs that contribute to its hummocky texture. The intercrater
plains unit is inferred to consist of crater and basin ejecta deposits,
volcanic flows, and possible pyroclastic deposits that have partly
resurfaced and smoothed older, highly cratered, crustal rocks. The unit
appears to be gradational laterally eastward with plains and terra
material, undivided, and vertically with intermediate plains material.
The intercrater plains material is probably about the same age as the
ejecta blanket around Beethoven basin (unit brl): both units have a high
crater density. That the plains unit is younger than Beethoven may be
indicated in some areas where the basin's ejecta blanket appears to be
partly obscured by the overlap or embayment of plains material. Spudis
and Prosser (1984) have suggested that Beethoven may possibly be late c3
in age or as old as early c2.

The age of the plains and terra material, undivided (unit ptu) is
probably equivalent to that of the intercrater plains material, and to
at least part of the intermediate plains material, though it was not
found in contact with the latter. The plains and terra unit, occurring
in the central and eastern parts of the quadrangle, was originally
mapped to the east in the Kuiper quadrangle (De Hon and others, 1981).
The term was there applied where differences in image quality prevent
clear distinctions between plains and terra materials. The name was
adopted in the Beethoven quadrangle for the same

reason. The unit intergrades to the west and south with intercrater
plains material and is interpreted to be of the same origin and
composition.

The intermediate plains material (unit psi) and smooth plains material
(unit ps) probably also consist of mixtures of relatively fine crater
ejecta and volcanic materials that appear to form a continuous sequence.
Both units are thicker than the intercrater plains unit. The
intermediate plains material is widespread in intercrater areas in the
west half of the quadrangle and fills floors of older craters and basins
in the southern part. Smooth plains material (unit ps), the youngest
plains unit, occurs as scattered patches in low areas and covers the
floors of many craters of c4 age and older. In some crater floors,
especially smaller ones, differentiation between smooth plains and
intermediate plains materials is difficult and the choice becomes
arbitrary.

Aside from a few small patches of dark material, and areas covered by
bright rays (stippled map pattern) around and emanating from c5 craters,
all plains units and the exterior rim materials of many craters have
albedos in the intermediate range. Collectively, these materials impart
a homogeneous appearance to the surface of the planet that is unlike the
contrast in bright highlands and dark maria of the Moon.

No terra material similar to that in the Kuiper quadrangle (De Hon and
others, 1981) was recognized in the Beethoven quadrangle. Its absence
may be due, in part, to fewer clusters of large young craters whose
coalesced ejecta blankets could have yielded the coarsely textured,
rough surfaces that characterize the unit in the Kuiper area. Also, the
visible effect of roughness is diminished by the higher sun angle at
which the Beethoven images were acquired.

BASIN AND CRATER MATERIALS

Coarsely lineated ejecta blankets from Beethoven and Raphael basins
dominate the southern part of the map area. The crater wall of Beethoven
is buried by its ejecta blanket (unit brl) and by plains materials
(units pi and psi). Although the ejecta blankets from both basins are
extensive, they are highly asymmetrical and deeply embayed in places by
intercrater plains and younger plains units. These embayment relations,
together with the discontinuous and subdued appearance of the rim crests
and interior walls of the basins, suggest that they are relatively old
impact structures. Morphologic appearances may be misleading on Mercury,
however, because of the planet's high temperature and gravity field
compared with, for example, those of the Moon. Both of these conditions
may promote, particularly on large structures (Trask, 1976), more rapid
isostatic adjustments that would be expressed by subdued topography and
the premature "aging" of once-large topographic features. Crater counts,
on the other hand, tend to support observed stratigraphic relations.
(See Description of Map Units.)

In addition to the large single-ringed basins of Beethoven and Raphael,
at least eight double-ringed craters exceeding 100 km in diameter occur
in the quadrangle. These craters range in age from c1 to c3 and, on a
minor scale, their ejecta blankets provide stratigraphic horizons useful
for the relative dating of material units in their vicinity. Two of the
youngest of the double-ringed craters, Durer (lat 22° N., long 119°) and
Vivaldi (lat 14° N., long 86°), have prominent and nearly continuous
inner rings whose diameters measure about half that of their outer
rings. Unlike some of the lunar multiringed structures, no vestiges of
additional rings are apparent around these craters.

Central peaks are common within craters of c3 and c4 age, rare in
craters of c2 age. Their origin may be genetically related to the inner
rings of larger craters and basins. Crater floors are underlain by a
zone of shattered and brecciated material formed by the shock wave
resulting from impact. Crater-rim material consists of decompressed
ejecta from the impact, whereas central peaks were probably formed by
the converging flow of slump material from the crater walls (Shoemaker,
1981). If a crater was sufficiently large, the converging flow resulted
in an inner ring rather than a central peak. An alternative model for
central ring or peak formation was discussed by Melosh (1983), who
suggested that they form as a result of rebound of fractured material
analogous to the jet produced by a stone dropped into water. Depending
on the size of the crater, the result is either a central peak or an
inner ring. The limiting

crater size for central peaks has been defined by Guest and others
(1979, p. 88) as about 150 km. This size limit seems to be generally
applicable in the Beethoven quadrangle with the exception of the ringed
crater Judah Ha-Levi (lat 11° N., long 109°), which has an inner
rim-crest diameter of about 80 km. Although this crater appears to have
two rings, its inner ring structure is morphologically fresher than the
outer ring, and it may have been formed by a separate and later impact.

Craters less than about 30 km in diameter were not mapped except for
those that are rayed and those occurring in chains and clusters
satellitic to larger craters and basins. These satellitic or secondary
craters (unit cs) are not distinguished as to relative age or origin.
(However, near the southwest map corner, elongate chains are radial to
their parent crater V![](media/image1.pct){width="0.125in"
height="0.18055555555555555in"}lmiki). In general, secondary craters
appear topographically fresher and occur closer to their primary sources
than do their lunar counterparts. This effect is probably due to the
fact that the higher gravity field on Mercury compared to the Moon has
resulted in higher impact velocities for crater ejecta (Gault and
others, 1975; Scott, 1977).

**STRUCTURE**

Neither faults nor scarps that are possibly associated with faults or
monoclinal folding appear to be common in the Beethoven quadrangle,
possibly because of the high sun elevation. The longest and most
prominent of these structures occur in the plains and terra material,
undivided, in the southeast quadrant of the map area. There, a series of
prominent scarps extends northeast from near lat 10° S., long 95° to lat
4° S., long 86°, over a distance of about 400 km. The inner ring of
crater Durer appears to be slightly offset on the north side by a small
normal or strike-slip fault.

Troughs and ridges are present throughout the quadrangle. Where the
troughs are not clearly radial to crater or basin centers, they may be
grabens; however, in most places they are difficult to distinguish from
linear gouges produced by impact ejecta at low-angle ballistic
trajectories. Some ridges resemble those on the lunar maria, but
generally they are less sharply defined. Ridges interpreted to be buried
rim crests of two ancient basins are partly visible almost due north of
Beethoven basin; the probable centers of the basins are near lat 11° S.,
long 127° and lat 2° N., long 124°.

**GEOLOGIC HISTORY**

Geologic evidence for the reconstruction of the evolutionary history of
Mercury is less complete than for the Moon and Mars, for which orbiting
spacecraft and landers have provided total or near-total coverage and
high-resolution images. However, available data allow certain parallels
to be drawn with respect to the bombardment and accretionary histories
of the three bodies. The geologic record shows a period of decreasing
meteoroid flux on all three, wherein the basins and large craters formed
early in their crustal evolution were superseded by impacts of
progressively smaller size. The relative paucity of mappable c5 craters
in the Beethoven quadrangle is indicative of the decreasing
crater-production rate in the younger crater classes. The low density of
small craters in the oldest class, c1, results from their destruction by
impacts and obscuration by ejecta and volcanic material over a long
period of mercurian history.

The intercrater plains and younger plains materials probably have mixed
origins, and they consist of both volcanic and impact ejecta-related
deposits. The plains materials accumulated mostly in low-lying areas and
have buried or partly buried older craters and surfaces. Their relative
ages and thicknesses are reflected by the number of craters visible on
their surfaces: where crater densities are high, the plains material is
relatively old or thin; low crater densities indicate relatively thick,
young deposits. Where superposed craters can be distinguished from
partly buried craters, relative ages of the plains units can be
established. Crater counts (Description of Map Units) indicate that the
intercrater plans unit, whose crater density is twice that of the
intermediate plains unit, is significantly older.

Whether the mercurian plains materials are analogous to volcanic flows
of the lunar maria is unknown. In this quadrangle, the former lack many
characteristics of mare

materials, including low albedo and strong albedo contrasts with other
units, lobate flow fronts, sinuous rilles, and numerous "wrinkle"-type
ridges and domes with summit craters. Possibly the plains units on
Mercury are similar to the Cayley Formation on the Moon and consist
largely of finely divided ejecta materials. Whatever the origin and
composition of the plains units in the Beethoven quadrangle, they
represent late stages in the crustal evolution of this region.

Other differences between the Moon and that part of Mercury observed in
this quadrangle are the absence in Beethoven of distinct highlands and
lowlands, as well as the preservation in the quadrangle of secondary
crater chains around older craters and basins (Scott, 1977).

The geologic history of Mercury has been summarized by Guest and
O'Donnell (1977), Davies and others (1978), and Strom (1979).

**REFERENCES CITED**

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

De Hon, R.A., Scott, D.H., and Underwood, J.R., Jr., 1981, Geologic map
of the Kuiper quadrangle of Mercury: U.S. Geological Survey
Miscellaneous Investigations Series Map I-1233, scale 1:5,000,000.

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.

Guest, J.E., Butterworth, Paul, Murray, John, and O'Donnell, W.P., 1979,
Planetary Geology: New York, John Wiley, 208 p.

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

International Astronomical Union, 1977, Working Group for Planetary
System Nomenclature, *in* 16th General Assembly, Grenoble, 1976,
Proceedings: International Astronomical Union Transactions, v. 16B, p.
330--333, 351--355.

Malin, M.C., 1976, Observations of intercrater plains on Mercury:
Geophysical Research Letters, v. 3, no. 10, p. 581--584.

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.

Melosh, H.J., 1983, Acoustic fluidization: American Scientist, v. 71, p.
158--165.

Scott, D.H., 1977, Moon-Mercury: Relative preservation states of
secondary craters: Physics of the Earth and Planetary Interiors, v. 15,
no. 2--3, p. 173--178.

Shoemaker, E.M., 1981, The collision of solid bodies, *in* Beatty, J.K.,
O'Leary, Brian, and Chaikin, eds., The New Solar System: Cambridge,
Mass., Sky Publishing Co., p. 33--44.

Spudis, P.D., and Prosser, J.G., 1984, Geologic map of the Michelangelo
quadrangle of Mercury: U.S. Geological Survey Miscellaneous
Investigations Series Map I-1659, scale 1:5,000,000.

Strom, R.G., 1979, Mercury: A post-Mariner 10 assessment: Space Science
Reviews, v. 24, p.3--70.

Trask, N.J., 1976, History of basin development on Mercury: Conference
on Comparisons of Mercury and The Moon: Lunar Science Institute
Contribution no. 262, p.36.

Trask, N.J., and Dzurisin, Daniel, 1984, Geologic map of the Discovery
quadrangle of Mercury: U.S. Geological Survey Miscellaneous
Investigations Series Map I-1658, scale 1:5,000,000.

Trask, N.J.,and Guest, J.E., l975, Preliminary geologic terrain map of
Mercury: Journal of Geophysical Research, v. 80, no. 17, p. 2461--2477.