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CONTENTS
Page
Abstract Al
Introduction 1
Previous work 2
Scope 2
Dat a sources 3
Stratigraphic terminology 3
Acknowledgments 6
Mare Imbrium and norther n Oceanus Procellar um 6
Introduction 6
Superposition relat ions 8
Mare ages on basis of small crat ers 14
Flooding of small crat ers 14
Morphology of small superposed crat ers 14
Other properti es 17
Color 17
Radar 17
Reflectivity 17
Correlations with time-str atigraphic unit s 17
Apenni nus-Ha emus region 19
Terra mater ials Imbriu m basin 19
Massif mat eri al 22
Materi al of Montes Archime des 23
Blocky ejecta 23
Lineat ed and smooth ejecta 23
Grooved mat eri al 24
Possible impact melt 25
Slump deposits 26Dark materia ls 26
Mare materi als 26
Mare and dark mant ling mater ial in Montes Hae mus 27
Sources 27
Terra east of Mare Serenitatis, west of Crisium, and north of
Tranquillitatis 27
Pre-Imbrian materi als 31
Possible Imb ri um effects 31
Internal versus basin origin of struct ures 31
Craters 34
Taru nti us region
Terr a units
Low albedo of some te rra uni ts
North ern Nectari s basin rim
Theophilus
Orient ale analogs
Secondary impact crate rs of Imbri um
Deposits
Post-Imbri um features
Central highlands
Grooves
Subcircular Imbri um secondary crate rs
Other possible secondary crate rs
Pri mary impact crate rs
Descartes mount ains
Othe r hummocky deposits and hills
Plain s deposits
Souther n Oceanus Procell arum
Fr a Mauro Format ion
Mare properties
Age
Color
Reflectivity
Thickness
Correlati ons of mar e properties
Age versus thickne ss
Age vers us color Color vers us reflectivit y
Reflectivity versus thic kness
Color versus thickne ss
Age vers us reflectivity .
Very red ter ra
Summ ary and conclusions
Imbri um impact i
Mare materials
References cited
ILLUSTRATIONS
T7i
FIGURE 1. Shaded relief map of part of the lunar nearside showing location of text figures
2. Geologic map of northern Oceanus Procellarum, Montes Harbinger, and Aris tarchus plateau
3 G l i f f h b i
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IV CONTENTS
FIG URE 12. Stereoscopic photo graphs of centr al par t of area mapped in figure 11A
13. Photog raph showing varie ties of ejecta and mare features on southeast -sloping flank of Montes A
14. Pho tog rap h of are a on flank of Ori ent ale basi n ana log ous to are a in figure 13
15. Geologic map of dark mate ria ls in part s of Apen nin us-Ha emus region, Mare Sereni tatis, and M16. Color-difference pho tog raph incl udi ng region map ped in figure 11
17. Geologic map of east ern Seren itat is, western Crisium, and nor the rn Tranq uill itat is region
18. Stereoscop ic pho tog rap hs show ing east -cen tral pa rt of are a covered by figure 17A
19. Photo graph showing par t of area mapped in figure 17
20. Phot ogra ph of area 900 km east-s outhe ast of Orien tale basin center
21. Geologic map of Tar unt ius region
22. Stereoscopic photo graphs showing south western corner of area in figure 21
23. Geologic map of part of nor the rn Nectari s rim
24. Stereoscopic phot ograp hs of par t of area mapped in figure 23
25. Stereoscopic phot ograp hs showing features of crate r Theoph ilus
26. Phot ogra ph of Orien tale secondary crat ers and basin deposits sout heast of Orienta le basin 27. Geologic map of par t of centr al high land s
28. Stereoscopic phot ograp hs of par t of centra l high land s
29. Phot ogra ph of Orien tale analog s of man y features in study area
30. Photo graph of crat er Struv e L
31. Photo graph of plain s deposits in floor of crat er Albat egni us
32. Geologic map of part of sout hern Oceanus Procel larum
33. Stereoscopic photo graphs of centra l part of area covered by figure 32A
34. Stereoscopi c pho tog rap hs of west ern pa rt of are a covered by figure 32JB
35. Stereoscopic phot ograp hs of easte rn par t of area covered by figure 32B
36. Color-difference photo graph includi ng area mapped in figure 32
37. Histo gram s showing relati ons between pairs of propert ies of mare soil mapped in figure 32
TABLES
TABLE 1. D, value s in the area s mapped in figures 2 and 3
2. Cra ter age assi gnme nts in the nort hern Oceanu s Procel larum- south ern Mare Imbri um region 3. List of mare uni ts mappe d in figure 32
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Stratigraphy ofPart of
the Lunar Near Side
G E O L O G I C A L S U R V E Y P R O F E S S I O N A L P A P
Prepared on belialf of the
National Aeronautics and. Space Administration
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UNITED STATES DEPARTMENT OF THE INTERIOR
CECIL D. ANDRUS, Secretary
GEOLOGICAL SURVEY
H. William Menard, Director
Library of Congress Cataloging in Publication Data
Wilhelms, Don E.
Stratigraphy of part of the lunar nearside
Apollo 15-17 orbital investigations Geological Survey Professional Paper 1046-A
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APOLLO 15-17 ORBITAL INVESTIGATIONS
STRATIGRAPHY OF PART OF THE
LUNAR NEAR SIDE
B y D O N E. W ILH ELMS
ABSTRACT
The geology of the part of the lunar near side west of longitude
50E. photographed by Apollos 15,16, and 17 has been remapped and
reinterpreted. Emphasis is on the strat igrap hy of the mare materi als
and on genetic and stratigraphi c interp retati ons of ter ra unit s and
landforms believed related to the Imbrium basin. The key data sets
are stereoscopic orbital pictures taken by the three Apollo missions,
Lunar Orbiter IV photographs of the Orientale basin, Earth-based
telescopic color-difference images, and the Apollo 16 rock analyses.In northern Oceanus Procellarum and southern Mare Imbrium, a
detailed stratigraphic sequence of 20 crater and mare units has been
determined. Working definitions of the Imbr ian-E rato sthen ian and
Eratosthenian-Copernican systemic boundaries based on this se
quence are proposed. The sequence is correlated with relative mare
ages that are calibrated against absolute rock ages, and values of
3.30.1 and =s2.30.1 billion years, respectively, are estimated for
the system boundaries.
The terrae of the north- central nea r side are dominated by the
rings and continuous ejecta of the Imbrium basin. The crest of
Montes Apenninus is pa rt of the main rim crest of the Imbr iumcrater of excavation, modified by slumps. Blocky primary basin ej
ecta lofted or thrust onto the Apennine flank grades outward to
lineated and smooth ejecta that flowed along the surface and over
rode pre-basin features and Imbrium-basin secondary impact cra
ters. Grooves in the overridden high terrain are flow lineations in the
continuous ejecta blanket. Flowing deposits obstructed by pre
existing terrain apparently piled up as small knobs and ridges. Im
pact melt was deposited on the Apennine flank and inside the basin
on the Apennine bench; parts of the bench deposits are superposed on
slump material, indicating slumping immediately after basin forma
tion. The terra east of Serenitatis, west of Crisium, and north andeast of Tranqui llitati s consists of overlapping deposits and inters ect
ing rings of pre-Imbrian basins modifed by superposition of Imbrium
secondary craters, secondary or primary deposits, and northwest-or
iented grooves and other landforms previously attrib uted to faulting.
In Maria Serenitatis and Tranquillitatis and on bordering terrae,
the oldest dark units are mare and dark mantling materials that
appear both red and blue on color-difference photographs. An early
several levels, and so have no common
mantling materials have flowed from one
localities. Superposition of mant les on
telescopic properties.
The central highlands, northern Nect
outer terrae were largely shaped by Im
Imbrium-radial grooves appear on the st
consist of coalescing elliptical seconda
grooves and ri dges were formed by flow ofVery few fault s were found in the terr ae o
With increasing distance from Imbrium, t
ters appear more circular, more widely s
sharper. Many sharp and degraded crater
impact craters here and elsewhere are n
Imbrium. Complex and diverse land
seemingly superposed on irregular crat
partly fill craters, and various basin-rad
explained by the near ly si multan eous imp
ejecta fragments a nd by interacti on wit h
pits near the Apollo 16 site are Imbriumposed on Nectaris basin ejecta, but the De
at the site could have been emplaced a
primary ejecta, as suggested by others. Su
other thick, hummocky deposits including
and also contri bute d to some of the l ar
transition zone between continuous Imb
featu res. D ista l plain s deposits are probab
ondary ejecta. Some small plains patche
could be of Orientale origin.
Southern Oceanus Procellarum include
mare units and terra islands geologicallyColor and reflectivity correlate closely
units being dark and red units light. A
mature, and composition is the only facto
most units. A few anomalously bright
contaminated by underlying terra materi
crystalline fragments. A few anomalousl
been contaminated or may contain titan
h ti l ti lt f
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A2 APOLLO 15-17 ORBITAL INVESTIGATIONS
photogeological tec hniq ues is the pr incipal topic of thi s
chapter. Subsequent chapters, by other authors, de
scribe remote-sensing studies (chapter B), crater ge
ometry (chapter C), and experimental photogrammetry
(chapter D) and include results from earlier Apollomissions as well as the last three.
PREVIOUS WORK
The Apollo orbital photographs provide a close look
at an area that has been studied geologically for many
years starting with Gilbert (1893). Astronomers
Baldwin (1949, 1963) and Kuiper (1954, 1959) also contributed many geological insights in their general
lunar studies. Geologic mapping in the space age began
with three near-side maps by Hackman and Mason
(1961), followed by an intens ive p rog ram of detai led
mapping based on systematic application of strati-
graphic principles developed by Shoemaker (1962) and
Shoemaker and Hackman (1962). Maps at 1:1,000,000
scale in the area covered by the present study were
prepared by Marshall (1963), Eggleton (1965), Carr(1965, 1966), Moore (1965, 1967), Hackman (1966),
Morris and Wilhelms (1967), Milton (1968), Howard
and Masursky (1968), Wilhelms (1968, 1972a), Scott
and Pohn (1972), and Elston (1972). The telescopic
phase of this m appi ng was summari zed by Wilhelms
(1970), and the res t of the pre-Apollo 15 ma ppi ng was
summarized and updated on a near-side map at
1:5,000,000 scale by Wilhelms and McCauley (1971).
Numerous other maps and topical studies cover parts
of the area, incl udin g large-s cale pre-mission map s
(Eggleton and Offield, 1970; Carr and others, 1971;
Milton and Hodges, 1972; Scott and others, 1972).
Among the achi evem ent s of thi s previou s work are (1)
recognition of the temporal gap between formation of
the Imbrium basin and Mare Imbrium, (2) correct in
ter pret ati on of the i mpac t origin of th e basin, (3) cor
rect volcanic int erpr etat ion of the ma re mat eria l, and
(4) correct gener al pr ediction of th e lithology of th e
rocks collected by Apollos 11, 12, 14, 15, and 17. The
lunar geologic framework established by these studies
gave direction to surface exploration by Apollo and
unmanned missions.
Despite the pre-Apollo photogeologic effort, however,
many aspects of lunar geology were not understood.
that was a consequence of (2) and
might have been avoided by more
tion of the principles of superposition
ticated crater countsentirely withi
photogeology. More timely and intenworkspecifically, on the Orientale
have mitigated the Apollo 16 error
tives to the volcanic inter pret ati on
othe r te rr a landforms. However, the
units at the Apollo 16 site probably c
unambiguously specified by remote
present u nder sta ndi ng is dependent
returned rocks. This reality illustrat
teraction between "ground truth" which can identify and classify lu
determine relative ages, identify p
pose multiple working hypothese
rarely prove origins (Greeley and
origins and absolute ages are learne
ration, photogeologists can then con
for testing.
SCOPE
This pap er prese nts a new set of d
interpretations for the terrae in the A
ing into account the Apollo and Lu
and other information acquired or in
ear lie r synoptic mappin g of the reg
McCauley, 1971). Many of the str a
and landforms observed in the terr
be interpreted logically by volcanic processes, but the Apollo 16 analyse
regarded as requiring impact interp
dame ntal ly new genetic inter preta
are required by the sample analyse
in their stratigraphy that have em
geology and radiometric dating are
includes more explicit and detaile
photogeologic reasoning than do ear
lunar mapping p r inc ip les (S
Shoemaker and Hackman, 1962;
Wilhelms, 1970, 1972b; Wilhelms an
Mutch, 1973; also see Varnes, 1974
abstract analysis of the logic of geo
eral).
For report purposes the overflown
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
or by material subunit except for the large crater
Theophilus (figs. 23, 25). The study area includes three
Apollo landing sites (15, 16, 17) and is near the otherthr ee (11, 12, 14), but the geology of th e sites is not
stressed because of extensive existing literature. The
division into regions is based partly on natural geologic
provinces and partly on the desire to retain the compi
lation scales for all maps (1:3,300,000 at the equator to
1:3,800,000 at 30 latitude, good mapping scales for
lunar studies in my opinion). The black and white re
production prohibi ts adequ ate port raya l of two super
posed units, so where dark mantling materials and
terra materials are both significant, separate maps are
drawn (figs. 11, 15).
The photographed strips (fig. 1) cover two principal
features, the volcanic maria and the Imbrium impact
basin and its flanks. The Apollo 15 and 17 strips of
photographs on one hand and the Apollo 16 strip on the
other, although oriented differently and separated
widely in most of the area, happen to compose a radial
sample of the Imb riu m basi n and its peripher y. The
Apollo 15 and 17 strips cover the basin from its buried
center to a point about 2,000 km from the center except
for a mare-covered gap. The Apollo 16 strip, which
makes an obtuse angle with the radial directions, cov
ers the basin periphery from about 1,350 km from the
basin center in the west to about 2,350 km at the bor
der of Mare Fecundi tati s. I nner basin feature s are de
scribed first in this paper and outer, mostly secondary-
impact features in later sections. Mare materials are
described in detail only in the first, second, and last ofthe seven regions. Par t of Mare Tranqui llit atis th at
was photographed by Apollo 15 west of long 39 E. is
not discussed because of a photographic sun illumina
tion too high to provide new information. Summaries
and conclusions about the detailed regional studies are
collected at the end of the report.
DATA SOURCES
Vertical stereoscopic metric photographs taken by
Apollo 15, 16, and 17 mapping cameras are the chief
but not sole data source for this work. Stereoscopy aids
in estimating the three-dimensional form of contacts
and volumes of deposits and in qualitatively assessing
of the Moon's most significant
resolution (100-150 m) Orbiter
used to fill out small map areas Apollo strips (fig. 1) and were he
coverage, especially where the
were taken at sun illuminations
Furthermore, the most importan
terpretations of lunar terrae has
tively unmodified Orientale ba
Orbiter IV but not Apollo. An
reinterpret the near-side terrae
exposed within them, but many
that were not resolved until c
Orientale were examined in de
report includes nume rous phot
distances from Orientale that ar
tances of similar features from
Apollo panoramic photograph
resolution than the mapping pho
check certain detailed relations b
to areal map pin g because of the
Impo rta nt data for studies of th
in color-difference image s (Wh i
pared by combining Earth-bas
graphs taken at two wavelen
trav iol et end of th e spect rum (0
maximum at about 0.37 /urn) an
infrared end (0.73 to 0.90 jam
about 0.82 /xm). The resulting im
blue ness or rednes s of surface
wavelengths: relatively blue arrelatively red areas are bright.
such areas are referred to for s
"red" although these terms are
lunar colors are reddish.
STRATIGRAPHIC TER
Ages of lun ar mate rial unit s afollows. Pre-Nectarian units are
taris basin. The Nectarian Syst
of the Nectar is basin and other,
older than the Imbrium basin
Wilhelms, 1975). The term pre-
to pre-Nectarian plus Nectarian
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A4 APOLLO 15-17 ORBITAL INVESTIGATIONS
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
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A6 APOLLO 15-17 ORBITAL INVESTIGATIONS
stratigraphic system, usually considered to consist of
mat eri als of rayed cra ters. New workin g definitions of
t he I mbr i an - Er a to s then i an and E r a to s then i an -
Copernican boundaries are proposed in the following
section.
ACKNOWLEDGMENTS
This stu dy was conducted on behalf of the N atio nal
Aeronautics and Space Administration from 1973 to
1976. Most of th e work was done as pa rt of Exp er ime nt
S-222, H. J. Moore, Principal Investigator, under
NASA contract T-1167B. The regional studies that
provided important feedback were performed underNASA contract W13,130. The work was facilitated by
the excell ent base maps of the LOC serie s pre par ed by
the Defense Mapping Agency, wh
detail needed for the present purpo
sentational fidelity and locational
uscript benefited greatly from revi
and H. J. Moore.
MARE IMBRIUM AND NOR
PROCELLARU
INTRODUCTIO
The nor thwe ster nmos t area of
graphed by Apollo includes the(Moore, 1967), Montes Harbinger
ma re of Ocea nus Pro cell arum (fig
D ETA ILED SEQ U EN C E
Ca Ejecta and secondary-crater
materials of crater Aristarchus
Csk Secondary-crater materials
of crater Kepler
Cp Materials of crater Pytheas
Csc Secondary-crater materials
of crater Copernicus
Edi Materials of crater Dioph antus
Em 3 Eratosth enian mare material,
youngest
Em2 Eratosth enian mare material,
intermediate age
Ede Materials of crate r DelisleEe Materials of crate r Euler
Emi Eratosth enian mare material,
oldest
Et Materials of crater Timocharis
Ese Secondary-crater materials
of crater Eratosthenes
El Materials of crate r Lambert
Imi Imbrian mare material,
intermediate color
Ik Materials of crat er KriegerImr2 Imbrian mare material, red,
younger
Imrj Imbrian mare material, red,
older
Idr Dark mantling material, red
Ip Wall and secondary-crate r
materials of crater Prinz
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
tur es of thi s region, studied by a varie ty of remo te sen s
ing techniques (Zisk and others, 1977), include a
markedly reddish mantle that may be a loosely frag-mental deposit, numerous sinuous rilles, and other en
dogenic features. The part of Mare Imbrium photo
graphed by Apollo (fig. 3), especially its well-developed
volcanic flow features, has also been extensively
studied (R. G. Strom, fig. 18 in Kuiper, 1965; Moore,
1965; Carr, 1965; Fielder and Fielder, 1968; Whitaker,
1972a, b; Hodges, 1973; Young and others, 1973a, b;
Schaber, 1973; Schaber and others, 1975, 1976; Boyce
and Dial, 1973, 1975; Boyce and others, 1975). Thepresent study integrates the stratigraphic conclusions
of these works an d adds new observati ons of ma re a nd
crater units made on the excellent Apollo photographs.
The terr a materi als, which are pa
rings exposed in relatively small
cussed.The ejecta blanket of each crate
ally continuous layer of mat eri al
position in the lunar stratigraphic
craters and their ejecta form depo
poraneous with each primary crat
on most lunar geologic maps, the
of cra ter s are tog eth er classed as
For example, m ate ria ls of all raye
lumped as crater mat eri als of theand all nonrayed post-mare crat
signed to the Eratosthenian Syst
Hackman, 1962; McCauley, 1967;
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A8 APOLLO 15-17 ORBITAL INVESTIGATIONS
FIG URE 3.Geologic map of par t of sout hern Mar e Imbrium. Expla
Fe atu re nam es can be determ ined from geologic uni t symbols an
Apollo 15 mapping camera frames 595-602, 1002-1013, 1144-11
this report, 12 individual craters larger than 15 km are
ranked in their proper stratigraphic place among eight
mare or dark mantling units.
This detailed stratigraphic sequence was determined
data on small superposed crater
to locate additional boundaries.
photographs were re-examined,
crater-density contacts not prev
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
2063-2079, 2174-2192, 2330-2337, 2460-2475, and 2734-2742; Apollo 17 mapping-cameraframes 2115-2123, 2278-2296, 2714-2735, 2907-2932.
Fielder, 1968; Schaber, 1969, 1973; Schaber and of old redd ish Imb ri an mar e ma
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A10 APOLLO 15-17 ORBITAL INVESTIGATIONS
FIGURE 4.Young lava flows in Mare Imbrium (white arrowheads). Fine texture visible on most mare surfaces. SCopernicus (500 km in direction of black arrow) have cast conspicuous "herringbone" ejecta away from Copernicuscraters of crater Euler partly visible along lower left edge. Apollo 15 mapping-camera frame 1157, sun illuminationabove horizontal.
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
FIGURE 5.Crater Euler, 27.5 km diameter (E). A tongue of intermediate-age Eratosthenian mare material co
(arrow) cuts across the southe rn ejecta and isolat es a patch of ejecta. Copern icus seco ndari es (C) are super p
Lobate flows of youngest Erato sthe nian bas alt containing lava cha nnels t runc ate west ern ejecta of Eule r (arr
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A12 APOLLO 15-17 ORBITAL INVESTIGATIONS
FIGUR E 6.Crater Lambe rt, 30 km diamet er. Ri ng structu re south of Lambe rt is Lamber t R. Ejecta and secondary
mare materials in some places (A, B) but flooded by mare in others (C, D). The flooding at C was by thick flo
Eratosthenian mare unit, whereas at D the flows (oldest Eratosthenian mare) were thin and did not obliterate
at D contains a sinuous rille and possibly small endogenic pits and a volcanic ridge (between letters D and
featu re (arrowh ead) is in the older uni t to th e east. Se condary crat ers at E seem to be oute r second aries of E
southe ast and, like Lamb ert secondaries, are flooded by the oldest Eratos then ian mar e material . Apollo 15 ma
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
FIGURE 7 C D li l ( b 25 k ) d Di h (b l 18 5 k ) Th i di E h i
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A14 APOLLO 15-17 ORBITAL INVESTIGATIONS
mare u nit (inter mediate Erato sthenian) flooded the
southern and western ejecta of Delisle (as noted by
Moore, 1965) but did not flood materials of the im
mediate ly adjacent Diophantus. Secondaries of
Dioph antus t rans ect a sinuous rille in the part of theintermed iate Erat osthe nian mare unit tha t floods the
southern Delisle ejecta. Both craters are superposed on
the younger Imbrian red mare unit. Secondaries of
Diophantus are also superposed on the youngest
Eratosthenian mare unit. Thus the age sequence here,
from oldest to youngest, is younger red Imbrian mare,
Delisle, intermediate Eratosthenian mare, youngest
Eratosthenian mare, Diophantus.
The crater Timocharis is also probably older than theold Eratosthenian mare unit that embays Lambert;
that unit seems to truncate outer secondaries of
Timocharis (fig. 8). Secondary craters of Era tos then es
also overlie the two Imbrian mare units in the
sou the ast corn er of th e map a rea (fig. 3B) but are trun
cated by the old Eratosthenian unit (fig. 8).
Ejecta of the cr ate r Krieg er overlies the younger
Imbrian red mare and is in turn overlain by the oldest
Eratosthenian unit and probably the intermediate-color Imbrian unit (fig. 2B). Therefore, Krieger is Im
brian in age but younger than the Imbrian crater Prinz
that formed before the dark, reddish mantle.
Some small craters can also be ranked by relations to
mare units but are not included in the detailed se
quence. For example, the Eratosthenian crater at 30.5
N., 21 W. (Carlini B) is superposed on the younger
Imbrian red mare unit but is embayed by the inter
mediate Eratosthenian unit. The entire periphery ofthe Eratosthenian crater at 21.5 N., 39.5 W. (Brayley
C) is embayed, whereas the small adjacent crater
(Brayley E, unmapped) is completely untouched
(Neukum and others, 1975a). Four other mapped small
Eratosthenian craters are superposed on all nearby
units. Four small mapped craters are embayed by Im
brian mare materials, and so are also Imbrian.
In su mmar y, superposition relat ions yield the follow
ing stratigraphic relations:
Diophantus
Youngest Eratosthenian mare material
Intermediate Eratosthenian mare material
Delisle-Euler
The ambiguous cases can be
frequency counts of small superpos
and Konig (1976) determined that
than Euler and Eratosthenes you
Other relations found by Neukumwith those determined here; their
region is:
Aristarchus
Copernicus-Diophantus
Delisle
Euler /
Timocharis-Eratosthenes
Lambert
Ambi guit ies in the resul ts of Neuresolved by the superposition of
daries on Diophantus (fig. 7)
Timocharis secondaries on those o
8). Superposition relations among
ditional craters to the sequence in
tem that cannot be dated by relatio
rials (Kepler and Copernicus lie
area):
Aristarchus (very fresh secondall units)
Kepler (secondaries superpose
Pytheas (superposed on Coper
Copernicus
Diophantus
MARE AGES ON BASIS OF SMA
FLOODING OF SMALL C
On good photographs many smal
with subdued yet disti nct rim s app
material that spared the craters' inte
craters are flooded nearly to the
deep riml ess pit s. According to th
(1970) the craters ar e Eratos then
size would be more subdued if Im
sharp er and brigh ter if Copernican
by the mare on Eratosthenian crate
apparently "normal" population of
nican craters shows that the
Eratosthenian.
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FIGURE 8.Stratigra phic relations between oldest Eratosthe nian mare mate rial and secondary crater of Timocharis (large crater, 34 km diameter) and Eratos
northeast-trending flow texture, truncates Timocharis secondaries (upper arrow). Timocharis secondaries may be superposed on Eratosthenes secondarie
parts of Apollo 15 mapping-camera frames 0600 (right) and 0602; sun illumination from right (east) 2 above horizontal at center of right frame.
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A16 APOLLO 15-17 ORBITAL INVESTIGATIONS
FIGURE 9.Area in northern Oceanus Procellarum covered by approximately the eastern two-thirds of figure
largest craters are embayed by mare material (e), some are superposed on mare material (s, c) and one crate
partly superposed (x) . The unit which crate r x overlies is red mare mat eria l of Imbr ian age; the embaying
Eratosthenian mare material. The craters superposed on the blue unit are probably Copernican in age (c). Ap
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
TABLE 1.DL values of mare material units (Boyce and others, 1975)in the areas mapped in figures 2 and 3
[A few obviously anomalous measurements have been excluded. The uncertainty rangesgiven by Boyce and others (1975) for each measurement average plus or minus 35 and allbut a few range between 20 and 50]
Mare material unit D1 Numb er of points Average D1
Youngest Eratostheni an 140-195 12 165Intermediate Eratost henian . _ 170-21 5 13 200Oldest Eratosthenian 210- 245 21 220Intermediate-color Imbr ian 255 1 Smal l samp leYounger red Imbrian . 240 -26 0 9 250Older red Imbrian ._ 270 -38 5 16 310Dork, red mant ling mate ria l . - 360 1 Small sample
measured on islands of old surfaces too small to map,on secondary impact craters to which the Soderblom-
Lebofsky-Boyce method may not apply exactly, or on
craters whose ejecta is flooded by a thin unit and whose
unflooded interior slopes tell the age of an older buried
unit (fig. 9). A few additional anomalies remain, but
the match is so close th at I am convinced of th e valid ity
in this region of the crater-morphology technique of
determining relative ages.
Schaber (1973) reported DL values of the threeEratosthenian units as 23520, 1755, and 1605
meters (his phases I, II, and III). Schaber and others
(1976) proposed that each of these phases represents a
rapid and extremely voluminous eruption. The wider
range ofDL values in table 1, however, suggests that
each unit consists of many discrete flows erupted over a
long time.
OTHER PROPERTIES
COLOR
Color as displayed by the color-difference photo
graphs taken by Whitaker (in Kuiper, 1965; Whitaker,
1966, 1972a, b) clearly correlates with mare units in
this region (fig. 10). There is a progression from rela
tively reddish to relatively bluish with decreasing age,
except for the youngest Eratosthenian unit, which isslightly more reddish than the next oldest (Schaber
and others, 1975). The Imb ri an uni t of int erm edi ate
color apparently fits the sequence on the basis of
superposition relations and one DL value. Generally
the Imbrian units are reddish and the Eratosthenian
bl i h lth h ll t h tl f t
The lava flows that flood the
crat ers west of the Ar ist arc hus
strongly blue, whereas adjacent s
similar Eratosthenian craters are
hence, thin flows are capable of
colors and imparting their own colo
is the material detected by the
primary and secondary craters, ho
the u nder lyi ng mate ri al an d sprea
ferent color upon the near-surface
RADAR
Schaber and others (1975) have
relation between diffuse echoes o
transmissions at 3.8- and 70-cm
geologic units in Mare Imbrium.
youngest Eratosthenian flows ha
polarized echoes at the 70-cm wav
intermediate Eratosthenian unit alnotably th e tongue s outh west of L
this could be part of the youngest
West of 40 longitude (fig. 2A), the
tion of 3.8-cm echoes between the
and mare materials (Zisk and oth
REFLECTIVITY
The property of reflectivity was
mapping criterion in the area. For
to correlate with color: blue units
bright. Therefore the progression h
The reddish mantle, however, is v
because of its content of devitrif
others, 1977). These interrelations
discussion of southern Oceanus P
CORRELATIONS WITH TIME-STRA
Traditionally, rayed craters hav
the Copernican System and unr
posed on mare materials to the Er
More exact definitions of the
thenian boundary have never been
h E h d l
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A18 APOLLO 15-17 ORBITAL INVESTIGATIONS
FIGURE 10.Area mapped in figures 2 and 3 (outlined) showing color differences between wavelengths of 0.31 to 0
0.73 to 0.90 ttm on the oth er. Da rk is blue, lig ht is red. Courte sy of E. A. Whi tak er (Whitake r, 1
has differed in detail (Wilhelms and McCauley, 1971;
Schaber, 1973). The stratigraphic relations amongin this area can then remain unc
Timocharis and Euler remained
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
TABLE 2.Crater age assignments in the area (figs. 2 and 3)
[W/M = Wilhel ms and McCauley, 1971]
CraterPrevious
assignment ReferenceRecommended
assignment
Aristarchus Copernican . -Moore, 1965; W/M Copernican.Kepler _ -Copernican . -Hack man, 1962; W/M -Copernican.Pytheas . Copernican . Carr, 1965; W/M Copernican.Copernicus Copernican Shoemaker and Hackman,
1962; W/M.Copernican.
Diophantus _ Imbrian' Moore, 1965 Eratos thenia n.Eratosthenian W/M
Del isle . . Imbr ian ' -Moore, 1965 Era tos the nia n.E ra to st he ni an - . W /M
Euler - -Copernican Carr, 1965; W/M Eratos theni an.Timocharis __ . -Copernican _Carr, 1965; W/M Eratos theni an.Eratosthenes . Eratosthenian . . . Shoemaker and Hackman,
1962; W/M.Eratosthenian.
Lambert Erat osth enia n . Carr, 1965; W/M Eratos theni an.
'Moore (1965) designated the materi als of Dioph antus and Delisle as the Diophan tusFormation, meaning older than some mare materials but younger than others.
Eratosthenian boundary has been regarded as the top
of the mare mat eri al in roughl y the easter n third of
figure 3B that is overlain by secondary craters of the
crater Erat ost hene s and overlies mater ial s of the Im
brian crater Archimedes (Wilhelms, 1970). This mare
material, mapped here as red Imbrian of both ages(map symbols Imr t and Imr2), includes DL values 250 to
360. Eratosthenes is overlain by mare material that
has to be considered Era tos the nia n (if not Copernican) ,
which hasDL value s of 210 and 230 (oldest Era tos the
nian unit, sout heas t of Lamb ert , fig. 6). Ot her large
stret ches of the sam e mare un it also hav e the se DLvalues, and only three measurements are larger than
230. Accordingly, I propose that mare units with DL
values of 230 and smaller be considered Eratosthenian,units 250 and larger Imbrian, and units with inter
mediate values be assigned according to the weight of
other evidence. All mare units which have been dated
radiometrically are Imbrian in this scheme, except
that sampled by Apollo 12 (DL 21020; Boyce, 1976).
Craters in the intervening range such as Lambert are
best retained as Eratosthenian unless proved other
wise.
If the maria here are Eratosthenian, the Eratos-thenian-Copernican boundary lies above the youngest
Eratosthenian unit and has DL values smaller than
140. No lunar maria1 are known to have smaller DLvalues. Unrayed craters younger than the youngest
Eratosthenian unit, such as Diophantus, may be re
tained as Eratos theni an pending more st udy of super
mined radiometrically on returne
ti mat es the ages (in billions of y
and 190 to be 2.60.3, between
3.20.1, and between 241 and 26the Imbrian-Eratosthenian bound
between DL 230 and 250 would
and the Eratosthenian-Copernica
DL 140 or less would be about 2.
APENNINUS-HAEMUS
TERRA MATERIALS IMB
The ter ra uni ts of the no rth- cen
are almost entirely par ts of the
circular basin and its flanks. Th
Apollos 15 and 17 includes a rad i
from a point on the Apennine ben
Hackman, 1964, 1966) within the
that rim (Montes Apenninus), an
transitions on the Apennine flank
to the western edge of Mare Tra
pact origin of th e basin and th e gmaterials were established by
1893; Baldwin, 1949, 1963; Shoe
1962; Hartmann and Kuiper, 19
1966). Rema ini ng questi ons abou
materials are considered here
stereoscopic photographs and com
ter exposed Orientale basin. Ana
brium are also displayed by th
philus discussed under the headinBasin Rim."
The cur rent gene ral pictur e of
materials is as follows. Terrestr
indicate that crater rims and pr
are structurally uplifted, partly o
with ejecta in a stratigraphic o
from the original order in the
hoemaker, 1959; Roberts, 1966
1968; Moore, 1971, 1976; Gaultravels outward from the basin
curtain , depositing mate ria ls clo
and distal materials last (Shoema
1975; Oberbeck and others, 1974
ejecta is also the last to leave the
tion occurs in reverse order fr
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A20 APOLLO 15-17 ORBITAL INVESTIGATIONS
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
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A 2 2 APOLLO 15 -1 7 ORBITAL INVESTIGATIONS
in the resulting deposits from predominantly primary
ejecta to predominantly local material excavated by
the secondaries. Many relations are explained by the
fact that the inner materials override the outer mate
rials, even though deposited earlier, because theirmomentum carries them outward behind the advanc
ing curtain of ejecta.
The principal remaining problems may be grouped
in two categories: (1) the origin of basi n rings, pa rti cu
larly the quest ion of which rin g best appro xima tes th e
rim crest and related questions about depth and
volume of the excavation and ejecta; and (2) the exact
na tu re of the trajector ies (surface or ballistic) and the
rela ted quest ion of the propo rtions of secondary an dprimary ejecta in the basin deposits at any point. Ring
origin and rim-crest location are discussed briefly in
the sections on "Massif Mat eri al, " "Mate ria l of Monte s
Archimedes," "Blocky Ejecta," and "Slump Deposits,"
and in the later section on "Theophilus," but they are
not major theme s of thi s paper. The rad ial s ample of
Imb ri um is favorable, however, for considerati on of the
emplacement processes including the primary-
secondary controversy and is a recurring subject in the
paper. Becaus e of the unce rta int i
scriptive term "continuous deposi
others, 1974; Oberbeck, 1975) is pre
ejecta" even in regions like the Ap
exposed secondary craters are scejecta must con sti tute a large propo
ejecta and lineated deposits.
Further controversy centers on
solid, melted, and gaseous materia
This and earlier studies (Moore and
identified impact melt on basin flan
was probably clastic; thus the ter
(Morri son a nd Ober beck, 1975)
(Moore and others, 1974) are approembrace primary and secondary eje
the two. The commonly used term
example, Lindsay, 1976) is less d
implies gas transport, a process no
important in emplacing lunar eject
MASSIF MATERIA
The Apennine front is characteriz
sive mountains, the Moon's largest (
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
steep, relatively smooth slopes that are bright at high
sun illumination. Their stratified appearance as re
ported by the Apollo 15 astronauts is probably a light
ing artifact (Swann and others, 1972; Howard and Lar-
sen, 1972; Wolfe and Bailey, 1972). Their massive
structur e indicates that they are par ts of the ri m of the
Imbri um crater of excavati on (Baldwin, 1963; Hodges
and Wilhelms, 1976; Wilhelms and others, 1977). The
amount of upth rus t or outt hrus t pre-Imbrian mat eri al
relative to basin ejecta in the massifs is uncertain
(Carr and others, 1971). The Apollo stereo photographs
of the tops of most massifs show textures like those of
the adjacent ejecta (figs. 11, 12, 13), but the thicknessof ejecta is not known; it may amount to the entire
height of th e massifs (Moore and oth ers , 1974).
MATERIAL OF MONTES ARCHIMEDES
Montes Archimedes (fig. 12) is a chaotically struc
tured elevated region south of the crater Archimedes.
Bright, smooth-sloped peaks protrude above jumbled
material, and textural elements tend to parallel theApennine front. The origin of Montes Archimedes is
tied to the question of original size of multi-ringed im
pact basins. For example, Head (1977) proposed that it
is part of the rim crest of the Imbrium crater of excava
tion, modified by slumping. Thus Montes Apenninus
would be external to the original crater, uplifted by
outward-directed stresses, and the steep frontal scarp
would be formed by faulting as Montes Archimedes
and the adjacent shelf moved toward the basin center.The alternative preferred here is that the Apennines, a
far larger structure than Montes Archimedes, approx
imate the main crater rim. Montes Archimedes would
thus have been formed inside the crater either as a
subsidiary crater rim nested inside the main excavated
cavity (Hodges and Wilhelms, 1976; Wilhelms and
others, 1977) or as a relatively surficial slump from the
Apennines.
BLOCKY EJECTA
The most extensive unit is blocky ejecta from the
Imbrium basin. It dominates the southeast Apennine
slope (figs. 12, 13), where it is coarse, and also occurs in
Montes Haemus. Originally it was named the hum-
material of Montes Apenninus
closely spaced imbricate faults. O
tions in orie ntat ion, spacing , a
ejecta are indicated diagrammasymbols. The concentric, more m
dominates in the southwest Apen
the knobby Alpes typ e domina te
5 east longitude.
The m ode of emp lac eme nt of th
not entirely certain. The Apenni
consists either of ejecta or of ou
by ejecta, for it grades outwa
clearly have flowed (figs. 11, 1coarse str uct ure an d a lack
produced by its impact indicate th
short, slow ballistic trajectories o
face, in accord wit h th e gener al p
of near -ri m primar y deposits. Ma
position at Orien tal e has te xtu re
tion an d not of st ru ctu ral def or
Alp es facies seem s to be a mix o
finer material and so is probablyIts more chaotic structure may in
tic flight and a different source t
facies. If lunar basins consist of
could leave the inner crater(s)
from the outer and fall back u
ejecta (Oberbeck, 1975). The Alp
inner ejecta and the Apenninu
ejecta, a relation suggested by
similar materials at Orientale (sources closer to the basin cente
Some concentric texture in Mo
to hav e formed by decelerati on
posits (fig. 13, t) as is common a
(McCauley, 1968; Hodges, 1972
1974; Scott and others, 1977; see
piled-up ejecta commonly resem
has been called "deceleration dun
Similar small, bright, blocky hillposits in Montes Haemus (fig. 1
from craters and other elevations
been overridden by deposits mov
(lat 12 N., long 15 E., and lat
sout h of Auwer s). However, the
i bl h b l k d f
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A 2 4 APOLLO 15 1 7 ORBITAL INVESTIGATIONS
FI GUR E 13. Vari etie s of ejecta and ma re featur es on sout heas t-sl oping flank of Monte s Apenni nus . Blocks alined up
as those betw een mo unt ain front (ap) and cra ter Conon (C) are part of the Ap enn inu s facies. More widely space
Alpes facies (Alpes Form atio n); h ere the y are alined radi ally awa y from basi n. At bottom of photo grap hs, kn ob
smooth facies (s). Grooves (g) probably we re formed by surface flow, and tr ans ver se ridg es (t) probably from dece
(m) cont ains na rro w fissures t ha t suggest contr actio n of cooling mat eri al; th is may be impa ct melt, as may othe r
transverse fissures (f) in other ejecta could also be contraction cracks. Dark mantling material (d), D-caldera (a
features (arrow) like those in Apennine Bench Formation (fig. 12) are post-Imbrium, mare-related features. Same
of Apollo 17 mappi ng- came ra frames 1821 (right) and 1 823; sun illu min ati on from right (east) 13 above ho
frame, 10 in left.
The lineated ejecta shows clear evidence of flow gen
erally away from the basin (shown by orientation of
dashes on fig. 11). Some lineations curve around obsta
cles. Most lineations in this area are narrow, but some
are distinct grooves (fig. 13, g) as at Orientale (fig. 14,
g) (Moore and others, 1974, figs. 5 and 7). The lineated
and smooth ejecta appear to grade from blocky or other
coarsely structured ejecta at both basins. The grada
tion could reflect a finer grain size or greater melt con
tent in the outer ejecta (Moore and others, 1974) or a
Grooves, on the average about 2 km
the basin and are straight or gentl
and slopes facing the basin are
grooved features, but some slopes f
basin are also grooved. Reflectivit
though some occurrences are cove
(mapped in fig. 15). Ejecta is ban
sides of some of the grooved hills.
Evidence in the area is insufficie
an erosiona l or a depositiona l origi
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
FIGURE 14.Area on flank of Orientale basin at same position relative to basin rim, si
azimuth (east-southeast), similar scale, and similar geology as the Imbrium area in figur
Crater Eichstadt (E) 50 km diameter. Topographic basin rim of Orientale is Montes Clera (co). Concentrically oriented ejecta near basin rim and Eichstadt grades outward
smoother, radially lineated ejecta (s) with occasional deep flow grooves (g). Transverse
of ejecta (t) are piled up where ejecta flow encountered obstacles. Concentric structu
inner ejecta may have a similar deceleration origin or may result from low original ej
velocities and trajector ies. Narr ow trans ver se fissures (f) simila r to those of the Imb
area are also present, but their significance is uncertain; they may indicate shrinkage
impact-melted material in ejecta. Part of Lun ar Orbiter IV frame 17 3-H; su n illumin
from right (east) 15 above horizontal.
presu mably are massifs of th at basin, but some are
Imbrium basin secondaries emplaced onlymomentarily before being overridden by a debris surge
(Oberbeck, 1975; Wilhelms, 1976). Some occurrences
are not strongly grooved but consist of single or alined
knobs ("volcanic domes," Morris and Wilhelms, 1967).
These knobby features may also have been overridden
and are included in the grooved unit (fig 11) The
tne impact that formed the Imbri
the lineated and smooth ejecSecond, cracks in some wavy surf
shr ink age of molt en mat er ia l (fig
comparable positions in the Orie
facies") is interpreted as impact
others (1974).
The thi rd and larg est expan s
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A26 APOLLO 15-17 ORBITAL INVESTIGATIONS
age cracks, and gentle, smooth-walled depressions that
suggest sub sidence of viscous fluid into under lyi ng
cavities (fig. 12, above symbol ab). Volcanism cannot be
excluded, but an impact origin is more consistent with
current understanding of Orientale (Scott and others,1977) and the lunar terrae in general. Fractured melt
overlies slumps from the Apennine front (fig. 12), in
accord with inferences by Dence (1971) that melt in
terrestrial craters is emplaced after slumping.
SLUMP DEPOSITS
Much evidence suggests that the hilly material im
mediately nor thwes t of the Apenn ine front slumpedfrom the mountains. The mounds and ridges nearest
the front roughly parallel the Apennine crest, are most
massive opposite the largest concavities, and in gen
eral can mentally be fit back into the front in jigsaw
puzzle fashion (figs. 11, 12, arro ws) . The ir finer
morphologymostly irregular imbricate structure and
a few massif-like hillsalso matches that in the
Apennines. Lineations radial to the front are probably
scour or flow grooves al ong the di rect ion of mov eme nt.Superposition relations show that the slumps formed
episodically. Superpos ition of th e impact melt shows
that major slumping occurred within a short time after
the basi n formed. Ne ar the head of Rim a Hadley, a
massive, linear slump ridge parallel to the front is
transect ed by a later hummocky ton gue of slump m ate
rial (Carr and others, 1971) perpendicular to the front
(fig. 12, black cross). The topog rap hy of th ese int ers ect
ing slumps matches "missi ng" part s of the Apenni necrest. The later, radial flow apparently was a fragmen-
tal mass that travelled farther than the earlier more
coherent slump. Long-continued movement toward the
basin centerthough probably regional subsidence
rather than true slumpingis indicated by grabens
parallel to the Apennine front that cut the mare mate
rial as well as the slumps (fig. 12, g).
DARK MATERIALS
The regions of Mar e Sere nit ati s mapped here (fig. 15)
and to the east (fig. 17) contain typical and long-
studi ed examp les of the t wo major morphologic types of
lunar dark material, mare material and dark mantling
t i l Th t d l ll d
the highland rim. The dark borde
younger than the brighter ce
Wilhelms and McCauley, 1971).
materials are level (marelike) in p
thought to indicate that they ovedark mare materials were believe
lighter ones on the basis of spars
analogy with the better understo
northern Procellarum-southern Im
cussed above, where the younger m
the darker. The Apollo photogra
tha t the lighter mare mater ials o
abut and embay the border mare
are younger (Howard and othermantling materials are also clearl
materials in most places; the level
may overlie old mare material, o
accumulati ons of dark mant lin g m
as will be discussed.
MARE MATERIA
Mare units are mapped (fig. 15)th ir ds of th e area of figure 11 m
bri um and nor the rn Oceanus Proc
tr al Mare S eren ita tis is composed
in which 18 D, values ranging fro
measured (Boyce and others, 197
presumably reflects a complex str
absence of strong color boundarie
red units (both Imbrian, map sym
could be tentatively distinguishedThe mar gi nal zone of Mare Sere
diverse th an the interior . The eas
margin in this area is the oldest
mar e materi al) a nd is a continua
that fill northern Mare Tranqu
Pli niu s are a of Howar d and other
others, 1972; Thompson and other
others, 1975). The unit slo
Tranquillitatis toward Serenitatifaulted by grabens. This slope pre
subsiden ce of cent ral Mar e Seren i
blue mar e mater ials west of the
younger Imbrian.
The western margin of Serenitat
E t th i bl t i
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
Mare Vaporum seems to contain the unit of
Eratosthenian or Imbrian age and intermediate color
and a similarly colored but clearly Eratosthenian unitthat embays deposits of the crater Manilius.
Thus the sequence here contains a red-to-blue pro
gression like that in the northern Procellarum-south-
ern Imbrium region, but some young units are not the
bluest and extensive blue units occur in the old part of
the sequence. As will be discussed in the section on
southern Oceanus Procellarum, color and reflectivity
correlate in mature mare regoliths, and both depend on
composition of the unde rly ing basalt . This expl ains
why the generalization that young lavas are dark could
not be correctly extrapolated to the present region
young lavas are dar k only if they ha ppen to be blue
(titanium rich). Blue old lavas are also dark.
The presence of the old blue materials here and not
in the northern Procellarum-southern Imbrium region
has been taken as an indication that erupted lunar
mare lavas progressed in time from blue in the east to
red in the center to blue again in the west (western
Oceanus Procellarum contains many young blue lavas)
(Soderblom and Lebofsky, 1972; Soderblom and Boyce,
1976). However, there are numerous exceptions to this
generalization here and elsewhere including to the
east in Sinus Amoris, where very old red materials are
exposed (fig. 17).
MARE AND DARK MANTLING MATERIAL IN
MONTES HAEMUS
Dark materials were deposited on most of Montes
Haemus at levels considerably higher than Maria
Serenitatis and Tranquillitatis (fig. 13). The terra
along the border of Mare Serenitatis is thickly mantled
by a deposit called the Sulpicius Gallus Formation
(Carr, 1966) that grades outward to a thinner blanket
(fig. 15). Small bright peaks protrude through all but
the thickest part s of thes e deposits. The mant le was
probably deposited even on high ground, for somematerial on steep slopes is streaked with dark as well
as bright material (the latter presumably derived from
the underlying bedrock). The thick deposits are dis
tinctly reddish (for example, Lucchitta and Schmitt,
1974). Unit Idr north of Menelaus is an arched, faulted
deposit (dark member of the Tacque t Form ati on; Ca rr
in both belts appear to be as old
red mare units along the Sereni
stratigraphic relation between reuncertain. In addition, a few sm
mediate or uncertain color and
mare, undivided (map unit m), a
young, probably Eratosthenian
surmounted by the "D-caldera"
1972d; El-Baz, 1973).
The distinction between mant
rials is unclear in this region.
would normally be mapped as m
of the ir overal l level surfaces, b
Imbrium basin materials; in the
scopic pictures, linear radia l st
show through. Most patches have
also reflect the subjacent topogr
gradational deposits mantle the
of thes e mant le s connect "la kes
flowe d from one la ke to ano th e
Other dark mantles (mapped as u
ciently like the adjacent terra,
bluish, as to suggest that thei
weakened by mixture with terra
Montes Haemus may have been
Imb ri an epoch of basa ltic volc
deposits"mare materials" bein
cum ula ted in sufficient thi ckne s
substrate to appear flat.
SOURCES
The region has an unusually la
lar craters, rilles, and cones wh
sources for the dark materials. A
lar crater in the mare (Greeley,
perched high on the terra (fig. 1
15.3 E.). The most common possi
numerous in the Sulpicius Gall
regular craters that appear too
photographs to be secondary im
picius Gallus rilles are likely a
much of th at format ion (Car r,
depressions could have formed
without eruption.
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A28 APOLLO 15 17 ORBITAL INVESTIGATIONS
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EXPLANATION
FIGURE 15.Geologic map of dark materi als in part s of the Apenninus-Haemus region, MareSerenitatis, and Mare Tranquillitatis. Based on Apollo 15 mapping-camera frames 398-416,
570-588, 977-995, 1119-1137, 1659-1678, 1800-1819, 2029-2048, 2143-2162, 2287-2305,
2426-2445, 2694-2712; Apollo 17 mapping-camera frames 796-813, 1221-1241, 1502-1522,
1805-1825, 2091-2108, 2252-2271, 2688-2708, 2882-2901; and color-difference photograph
reproduced in figure 16.
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FI GU RE 16.Color-difference photo grap h of regi on mapped in figure 11 (outli ned). Wav elen gth pair s 0.31 -0.40 ;u.m
is blue , light is red. Court esy of E. A. Whit ake r (Whitak er, 1966, 1972b).
Pohn, 1972; Scott and others, 1972; Head, 1974a). The
dominant northwest-southeast topographic "grain" of
the terrane (figs. 17, 18, 19) is radial both to Imbrium
(1,200 km to the northwest) and, in places, to the
nearby Serenitatis or Crisium basins. This grain and a
weaker, roughly northeast set of lineations follow the
most common "lunar grid" directions (Strom, 1964;
Scott and others, 1975) and have been ascribed to im
pact rejuvenation of endogenic st ruc tur es (Scott andPohn, 1972; Scott and others, 1972; Head, 1974a). After
considering the pre-Imbrium basins, I conclude that
Imbrium ejecta has played a major role in shaping the
terrane and that endogenic interpretations are unnec
essary. This conclusion relies less on direct observa
tions here which remain ambiguous than on obser
Sinus Amoris and the dark, blue, p
ma nt li ng deposit of th e Apollo 17 s
1972; Scott and others, 1972; Hinne
1973; Pieters and others, 1973; Tho
1973; Muehlberger and others,
others, 1974; Head, 1974b; Lucch
1975; Wolfe and others, 1975). In
dark mantling materials were foun
the Cr isiu m basin ri m jus t east of
the la titu de of Macrobius. A red E
unit apparently is also present (fig
Steplike distribution of patches of
nected by probable flows starting
stan tial ly above th at of the predo
was noted in the "lakes" perip
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
1973; Howard and Muehlberger, 1973; Scott, 1973b;
Young and others, 1973b; Muehlberger, 1974; Luc-
chitta, 1976). However, Mare Tranquillitatis south of
Dawes, a diverse area that includes a large sinuousrille, disc-shaped filled craters or domes, flow lobes,
large mare ridges, orthogonal faults in different units,
and degraded terra islands, was not well photographed.
PRE-IMBRIAN MATERIALS
The pre-Imbrium basins most likely to contribute to
the topography and lithology of the regi on are
Serenitatis, Crisium, and Tranquillitatis (Stuart-
Alexander and Howard, 1970; Wilhelms and
McCauley, 1971; Wilhelms, 1972a, 1973; Short and
Forman, 1972; Scott and Pohn, 1972; Head, 1974a).
The Tranquillitatis basin is very obscure but may have
contributed to the gross form of th e ter ra. The massifs
around the Apollo 17 landing site (figs. 17A, 18) are
part of the most conspicuous ring on the sou the ast side
of the Sere nit ati s basin, which m ay be double (Scott,
1972c, 1974; Reed and Wolfe, 1975; Wolfe and Reed,1976). Groups of irregular, overlapping craters north of
the area mapped here are alined radially to the south
ern Serenitatis basin and are probably its secondary
impact craters (Wilhelms, 1976). Crisium basin mas
sifs and radial l ineat ions (of possible non-C ris ium ori
gin) occur near the eastern map boundary (figs. 17B,
19), and hum moc ky ter ra in wes t of Pro clus (fig. 19)
that resembles the Alpes Formatio n of Imbr ium may
be ejecta of Cris ium. O therw ise, few feat ures att ri but able to Crisium have been identified in spite of the
proximity of the area to this large and relatively
youthful-appearing basin. Possible reasons are that
Crisium ejecta was ejected preferentially in other di
rections or that it is covered here by Serenitatis ejecta.
This younger age of Ser eni tat is , thoug h contrar y to
intuition because of its degraded appearance, is sup
ported by superposition relations outside the mapped
area. Its "old" appearance probably results frommodification by Imbrium ejecta.
POSSIBLE IMBRIUM EFFECTS
Five general types of small-scale topographic ele
of Orientale was selected (fig. 20
dary craters (p) and lineations
Orientale terrane. Lineations on
secondary pits (pi) apparently arejecta of the pits and partly flow
wi th thick mas ses of conti nuous
ward the basin (figs. 26, 29). Iso
from the basin are likely to be
gouges, but ori gin as flow groov
is also possible. If th e Orien tal e
degraded or poorly photographe
preted as faults. Thus regional
interpretations of landforms. Orientale scene, the pits east o
interpreted as Imbrium second
lineat ions as text ures of either
ejecta.
The mantles on the pre-Imbri
It) are also probabl y of Im bri um
and plains deposits that are
obscure the pre-Imbrian topogr
clearly to be of Imbrian age Orientale is surrounded at a sim
tles and plains in comparable
dational with secondary crater
continuous ejecta on the basin
symbols). The covered terrane
basin crater rims or of seconda
itself (fig. 20, c; compare figs. 26
and secondary basin ejecta may
and the former may flow outwaers (figs. 20, 26, 29). The Imb ri u
east of Mare Serenitatis presu
ap pa re nt if the zone bet w
Apenninus-Haemus region were
Orientale counterpart (fig. 20).
INTERNAL VERSUS BASIN ORI
Not only fine lineations but a
and mare-terra "shorelines" form
oriented northwest-southeast (fi
dogenic interpretations were ba
that these gross structures we
"squared off" to have been
Moreover, this trend is parallel t
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FIGURE 17.Geologic map of the eastern Serenitatis, western CTranquillitatis region. Based mostly on Apollo 15 mapping-cam
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
26.5 N
2278-2287, and Apollo 17 mapping-camera frames 289-314, 432-453, 1484-1506,2671 2692 L O bi IV f H 78 l
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FIG URE 18.Stereoscopic photographs sho wing east-centr al (right- central) par t of area covered by figure 17A. Arrow
landing site; d, dark mantling material. Labelled craters are Vitruvius (V), Maraldi (Ma), and Littrow (L). Sere
Apollo 17 site; sm aller hills in re main der of picture ha ve been termed "sculpture d hills." Rugged, ragged elev
and arro w with shaft at top of pict ure ("V itruv ius front," Head, 1974a) may be a Ser eni tat is basin ring . Typica
uni ts (fig. 17) are shown by geologic symbols . Hilly, pit ted, and line ated ter ra in (pi) on rim of Litt row and adjace
mant le (Itl) grades to thi nne r mantle with lineati ons on rim of crater Maral di (It). Str uctur e (white line) transv
help s give region an orth ogon al pat ern . Pa rt s of Apollo 17 mapp ing -cam era frames 444 (right) and 446; sun e
right frame, 14 in left. North at top.
Coarse and fine lineations not radial to Imbrium,
Serenit atis, or Crisi um also bound man y of the smal lknoblike mounds called "sculptured hills" or "corn-on-
the-cob" in Apollo mission terminology (fig. 18; Lunar
Sample Preliminary Examination Team, 1973). Major
scarps of the roughly northe ast- southw est trend seem
too irregular to be endogenic and are probably parts of
pre-Imbrian concentric basin structure l ike the
"Vitruvius front" (fig. 18; Head, 1974a). The small hills
could be Imbrium or Serenitatis ejecta blocked by ob
stacles, as is common around Orientale (fig. 29). Anorigin as an inner knobby facies of Serenitatis ejecta
compar able to the Alpes For mat ion of Im bri um is also
consis tent with the morphology and distri buti on of th e
small hills (Head, 1974a).
CRATERS
dued topography and irregular ou
to burial and deformation by thebasi ns. Origin by secondary imp
perhaps Serenitatis basin ejecta
likely. This conclusion is far from
supported by the Orientale analog
tical cr ater s of almost cer tain seco
occur (figs. 20, 26, and 29; discu
sections). Morphologies of the O
differ greatly because of different
tion by lineated and planar primejecta, but the craters are contemp
1976). This wide morphological ra
basi n shows th at secondar ies of
also resemble one another.
The recognition of craters as
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STRATIGRAPHY OF PART OF TH E LUNAR NEAR SIDE
FIGURE 19.Labelled craters are Maraldi (Ma, compare fig. 18), Romer (R), Macrobius (M), Tisserand (T), Proc
(L). Large mari a are Mare Tranqu illi tatis (MT) and Sinus Amoris (SA); cluster of mare domes is nea r scal
elevations, m; secondary impact crate r of Imbr ium or Sere nitat is basin, c. Other le tter symbols refer to typ
units or features (compare figs. 17, 18, 20). Large scarps (X) could be Imbrium basin ejecta (compare fig. 20
Apollo 17 mapping-camera frames 295 (right) and 302; sun illumination from right (east), varies from 20 ab
to 6 at left.
positions and ages. Becaus e of
tion of the Apollo photographs
not attempted west of long 39E
dent in the rest of the region on
of the better photographed
ged, and perhaps Tisserand, whose depth is inter
mediat e between depths typical of pri mar y and secon
dary craters.
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FIGURE 20.Area 900 km east-southeast of Orientale basin center. Labelled craters are Vieta (V)
(P), and Lacroix (L); the latter two are also on figure 26. Geologic symbols 1, p, t, It, pi, Ip, It, an
sam e me an in g as in Imbri um-in flue nced are a west of Mar e Ser en ita ti s (figs. 17, 18, 19). The
li t d t i ( i) th f Pi i C i t f th ti O i t l j t h th th
STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
EX PLA N A TI O N
A38 APOLLO 15-17 ORBITAL INVESTIGATIONS
hi h h h (fi 22) i li d i f h M i bl d P
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on high-sun photographs (fig. 22), in mantling deposits
(unit Itl) and in hilly ter rai n southeas t of nume rou s
irregular pits (unit pi). The radial lineations resemble
those north of Mare Tranq uil lit ati s and elsewhere at
similar distances from Imbrium, which is centered
1,950 km to the northwest. Hence it is inferred that the
mantling deposits are secondary or primary Imbrium
basin ejecta and that the lineated and pitted deposits
are Imbrium secondaries and their ejecta which are
superposed on pre-Imb rian ma ter ial s (probably of the
Nectaris and Crisium basins). The patch of lineated
material that seems to embay the crater Taruntius M
could be a tongue of Im br iu m deposits.
Volcanic or tectonic interpretations are also unnec
essary for the irregular craters. Secchi and Taruntius
L, for example, previously considered endogenic and
pre-I mbrian because of the ir shape and degradati on
(Wilhelms, 1972a), in fact resemble other large Im
brium secondary craters at comparable distances from
the basin.
LOW ALBEDO OF SOME TERRA UNITS
In the Taruntius region and adjacent areas, the
dichotomy between mare and terra that is distinct on
most of the Moon is blurred. Prev
lated between mare and terra-ma
for units having properties interme
cal wavy, textured, red, high-albed
flat , smooth, blue, dar k mare ma
maps by Wilhelms, 1972a, an
McCauley, 1971). The proposed rel
the lineations and pits in the unit
prop erti es shows the m to be of ter r
darkening is probably due to mantl
mare affinity. The stereoscopic ph
support the telescopically observed
1972a) that the flattest areas are
rugged areas bright. This relation
superposition of a mantle upon th
lowed by shedding from slopes,
clearly in Montes Haemus.
This hypothesis is supported by st
tions of dark materials that are
difference photographs (fig. 16). Blu
appear superposed on an otherwis
which includes both the main mar
dark and light terra materials. The
pear to have flowed from Mare Tra
Fecund itat is across the int erveni n
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STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
(arrows, figs. 21, 22). Tranquillitatis is obviously
higher than Fecunditatis; Defense Mapping Agency
topographic orthophoto map LTO 61C4 shows a differ
ence of about 200 m. The d escent of th e blue m at er ia l
occurs in a series of steps and cascades. In places it
forms smooth surfaces that probably represent deep
pools, while elsewhere it only thinly mantles the terra
material, darkening it but leaving the various textures
including rims of superposed craters still visible.
NORTHERN NECTARIS BASIN RIM
The overall ter ra topography nort h of Mare N ectar is
is that of the pre-Imbrian Nectaris basin rim, but ori
gins of the small er features includi ng diverse crater s,
Irregular pits, and hills (figs. 23, 24) are less obvious.
Most were previously believed to be volcanic (Elston,
1972; Wilhelms and McCauley, 1971) but are here in
terpreted as products of the impact of Imbrium basin
ejecta. Non- Imbr ium featur es include pa rt s of th e Nec
taris basin and relatively few large primary impactcraters. Stereoscopic photogr aphs of th e larg e (100 km)
crater Theophilus (fig. 25) provide a guide to the Im
brium interpretations, as do further references to the
Orientale analog (fig. 26). Mare and dark mantling
materials are inadequately photographed, so are not
discussed.
THEOPHILUS
Lunar impact craters and basins constitute a con
tinuum of impact features t hat incr ease in complexity
with increasing size (Gilbert, 1893; Baldwin, 1949,
1963; Stuart-Alexander and Howard, 1970; Hartmann
and Wood, 1971; Hartmann, 1972; Howard, 1974;
Hodges and Wilhelms, 1976). Therefore the generally
accepted interpretations of crater features can be
applied, with caution, to analogous but more complex
and puzzling feat ures of basi ns. T he high , rugge d cen
tra l peak of The oph ilus (fig. 2 5, A) proba bly formed by
instantaneous rebound after impact in response to ex
cavation of th e crater , a mecha ni sm advocated by
many workers (for example, Baldwin, 1963; Milton and
Roddy, 1972). The inn er rings of ba si ns may form in a
similar fashion, enhanced in layered target materials
(Hodges and Wilhelms 1976; Wilhelms and others
Head, 1974c; McCauley, 1977; Sc
and by extension, a similar int erp
nine Bench Formation advanced
The wall terra ces of large cr at
lar geme nt of the cra ter rim imm
ing. Hum mocky pa rt s of the Theo
are readily explained as slump fe
bly analogous to chaotic slumps
Apennine front.
The Theophilus crater rim als
brium basin rim. Like the Apen
mediate rim crest (fig. 25, F) is
pears smooth at fine scale, and h
inner par t of the ri m flank is a
raised ring that terminates at a
(G) at abou t 25 km or one-half a
rim. Montes Apenninus has a s
dropoff, although the raised mon
narrower125 km wide as comp
of 600 km from the basin center.
At the base of th e esca rpm ent (
rial apparently emplaced in a flui
contacts of some pools are shar p
gradational as if a widespread shee
hummocky (presumably mostly c
pooled in depressions. These r
studies of fresher lun ar crate rs
plains-forming mat eri al is impac t
place after depositio n of th e clasti
Wilshire, 1975). Cracked materi
pact melt was noted on the O
others, 1974) and Apennine flank
of these pools at Theophil us and o
that more may be present arou
basins than can be identified by
tures (Moore and others, 1974).
Outside the massive rim flank
pact melt are continuous deposi
craters, and discontinuous depos
formed by ejecta from the crate
exact mea ns of empl aceme nt i
morphology of th e ridg ed ejecta cl
could re sul t from flow of pr im ar y
face. Close to it, however, the
ringbone pattern (L) demonstrat
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EXPLANATION
FIGURE 23.Geologic map of the par t of the northern Nectaris basin rim covered by vertical mapping photographs taken by Apollo 16. Principal sources oframes 138-154, 416-433, 952-968, 1243-1258, 1636-1651, 1933-1946, 2156-2172, 2773-2787, 2930-2945. Lunar Orbiter IV high-resolution frApollo coverage.
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FIGURE 24.Stereopairs of area outlined in figure 23. The large craters in the left two frames are Isidorus (left) and Capella (with central peak); part of ma
right-hand edge (le tter U in its mar e fill). Letters designat ing features are the same as in figures 23 and 25; a thr ough g have analogs in figure 26. Apollo 16
424, 426 (partial), right to left. Sun illumination from right (east) 37 above horizon in center.
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FIGURE 25.Stereopairs showing features of crater Theophilus. To r ight (east> of Theophilus is cra ter Madier, 28 km diameter. Apollo 16 mapping-cam
and 431 (partial i, right to left. Sun illumination from right (east1
30 above horizon.
A. Central peak
B. Plains on crater floor
C. Hummocky material on crater floor
D. Wall terrace s
E. Hummocky wall material
F. Raised crater rim crest
G. Massive hummocky crater rim one-half crater- radius wide
H. Pool of plains ma teri al (probably impact melt) at bottom of slope of (G)
I. Anothe r pool of probabl e impact melt, less crat ered than (H)
J. Smooth ejecta, probably a coating of impact melt
K. Radiall y ridged ejecta
L. Herringbone pattern of secondary craters
M. Group of sharper secondaries with herringbone
N. Closely clustered secondaries with rugged rim in
P. Thin mantle of materia l on mare surface
Q. Material similar to P but thick and bright enough
ing unit
STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
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ejecta are also present in this outer regime (P, Q).
Hence there is clearly a general transition from pre
dominantly primary ejecta deposits on the inner rim
flank (G) to predominantly secondary deposits at theedge of the contin uous Theoph ilus deposit s (L- Q), bu t
the exact point of transition is not known.
ORIENTALE ANALOGS
Many Orientale features in a comparison area 1,200
km from the basin center (fig. 26), proportional to the
1,800 km of th e discussion ar ea from th e la rg er Im-
brium, resemble outer Theophilus features and land-
forms superposed on the Nectaris rim. Just as sharply
defined satellitic craters appear at about one crater di
ameter (100 km) from the rim cres t of The oph ilus (fig.
25, M), concentr ations of conspicuous cra ter s appea r at
about one basin diameter (930 km) from the topo
graphic basin of Orientale (Montes Cordillera). Some
Orientale satellitic craters are readily identified as
secondary by their moderately shallow depths and ir
regular outlines (fig. 26, a), like typical Theophilus
secondaries. Others are morphologically diverse and
have been interpreted as primary impact craters of dif
ferent ages (for example, Karlstrom, 1974). The diver
sity can be explained, however, by mutual interaction
(Oberbeck and Morrison, 1974) and differential burial
of secondary impact crat ers th at formed near ly sim ul
taneously (Wilhelms, 1976). For example, rims have
interacted to produce linear septa between the craters
(fig. 26, b). Similar interactions occur at Theophilus
but are har der to detect because of th e sma lle r scale
(fig. 25, N). At Orientale the typical craters are con
verted into flat-floored craters through burial by depos
its from the basin and from other secondaries (fig. 26,
c); craters that are located in depressions or are other
wise susceptible to burial are more deeply filled than
others. Coalescing craters form linear valleys (fig. 26,
e) or small, diverse clusters (f). Very sharp craters thatresemble primary impact craters could also be second
ary to Orientale (fig. 26, d), perhaps formed by frag
ments that were ejected at high angles and impacted
late, as proposed for craters at Tycho (Shoemaker and
others 1968) A random distribution of such high-
ria l excav ated by secondary i mpa
redistributed in debris clouds (
1974, 1975). Previously the e
around Orientale (for example, fiwere interpreted as volcanic, b
gous plains at Theophilus (fig. 25
be coincid ental man tl es of pos
materia ls.
SECONDARY IMPACT CRATE
Central to the Imbrium study i
of divers e crat er s mostly betw een
ameter (figs. 23, 24). Their rim cr
irregular in plan and range from
profile. Some appear so sharp th
investigators thought that they w
brium basin secondaries, althoug
recognized (Elston, 1972). Eggle
others, 1980) interpretation that
are Imbrium secondaries is suppo
sizes and shapes, their compoun
and Imbri um-r adial orient ation
ters, crater clusters, and accomp
Altho ugh the overall appear a
similar enough to suggest a gen
ual craters vary considerably in
and so the relation would not be
Theophilus and Orientale analog
secondary-crater morphology (figs
Orientale (fig. 26, a), but morp
others led to interpretations as e
impact crat ers of different ages.
was the interaction between cra
filling by deposits (c). Even sharp
(d) once considered young prima
secondary becaus e of th eir compo
ciated Imbrium-radial lineations,
is not certain either here or at O
Linear valleys that resemble graboverlapping secondary craters (e)
Hills once considered volcanic
by secondary-impact mechan isms
cra ter (b) on th e east wall of Cap
post I mbrium crat er "R") has a ru
A44 APOLLO 15-17 ORBITAL INVESTIGATIONS
by rim interactions. Intercrater septa are radial to Im- crater would have buried older c
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briu m on the nor thwe st flanks of Isidorus and Guten
berg (fig. 24, f). During nearly simultaneous impact of
closely spaced, smal l projectiles, ejecta of th e younges t
depressions, accounting for the
that secondary craters can be flo
posits.
STRATIGRAPHY OF PART OF THE LUNAR NEAR SIDE
i fl d b h
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DEPOSITS
Deposits of Imbrian age occur on much of the north
ern Nectaris rim. The nor the rn par t of the ma pped
area, consisting of pla teau s, low hill s, a nd depressio ns,
is heavily to lightly mantled (fig. 23, h). Plains deposits
appear transitional with the mantles (figs. 23, 24). A
few have sharp contacts and are flat and smooth (fig.
24, g, at top center). In contrast, little or no mantle is
observed on rugged terrain including the steepest mas
sifs, a few crater rims, the vicinity of the craters
Isidorus and Capella, and the terrain east of about
40.5E. longitude (the farthest from Imbrium). The de
posits are probably local materials that have been ex
cavated and ejected from secondary impact craters as
in the outer regi me of The oph ilu s (fig. 25, P, Q) a nd
Orientale (fig. 26, g). Abundant primary ejecta is un
likely to have reached this far from Imbrium by ground
flow, because the Nectaris rim would have intercepted
it. Therefore the deposits are probably ejecta from the
secondaries or, perhaps, primary ejecta that arrived in
comminuted form along ballistic trajectories (Chao and
others, 1975). Imbrium deposits are treated more fullyin the discussion of th e regio n to th e west.
A peculiar knobby or hummocky terrain (fig. 23, i, j)
is also mantled in places (i) though it appears rela
tively fresh in a trough cut in the Nectaris basin rim
(j). This knobby unit resembles the Alpes Formation of
Imbrium and may be the equivalent Nectaris basin
ejecta or Imbrium secondary ejecta blocked by the
trough as observed at Orientale.
POST-IMBRIUM FEATURES
Post-Imbrium primary impact craters in the area,
besides Theophilus, provide some information useful in
interpreting crater landforms. The small primary im
pact crater Capella A (fig. 24, R) has a compound out
line apparently due to collapse of part of its rim. The
prim ary origin (and Coperni can age) of Capell a A is
demonstrated by the line of small sharp secondaries to
the southwest. Another presumed primary, Capella J
(S), was influenced by the pre-ex
of Capella J that formed against
shaped crater is higher than the
When degraded, Capella J will p
moundsa high one on the horselow one opposite. Thus both Cap
mimic forms of secondaries.
The peculiar knobby or hummo
(T) next to Capella J may be ejec
ing Imbrium secondaries or from
tively the raised, structured floor
ter floor rebound. Rebounded cra
near mare boundaries (Pike, 1971
inderl ike uplift may explain ththe nearby crater Gaudibert (B
along the mare border is also ind
between the mare (U) and a h
terra (V).
CENTRAL HIGH
The central location and good
the tract described here have e
since the ear ly days of lu na r geol1893). The western two-thirds, c
basin, is characterized by "I
grooves and ridges radial to the
variously att rib uted to an "out
Imbrium (Gilbert, 1893; also Bald
Imbrium-related faulting or volc
hoemaker, 1963, p. 349; Har
Wilhelms, 1970, p. F15; Scott, 19
deposits and various small hills
interpreted either as related or a
to Imbriu m. Pa rt of the Fra Mau
wes ter n par t of th e area, a nd in
16 la ndi ng site, whi ch was select
plin g te rr a volcanic mat er ial s o
peculiar hilly and furrowed ter
cartes mountains (site selection
1972; Muehlberger and others,
that these units are composed of
nar Sample Preliminary Exam
FIGU RE 26.Orient ale secondary crater s and basin deposits southeast of Orien tale