wilhelms 1980 stratigrafy of part of the lunar near side gspp 1046a

8/6/2019 Wilhelms 1980 Stratigrafy of Part of the Lunar Near Side Gspp 1046a

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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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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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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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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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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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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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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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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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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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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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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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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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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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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

A20 APOLLO 15 17 ORBITAL INVESTIGATIONS


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25/76



26/76

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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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

A 2 4 APOLLO 15 -1 7 ORBITAL INVESTIGATIONS


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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


29/76


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



30/76


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


31/76


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.



32/76



33/76

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


35/76


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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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



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EX PLA N A TI O N


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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(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



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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


by rim interactions. Intercrater septa are radial to Im- crater would have buried older c


48/76

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.


i fl d b h


49/76

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

wilhelms 1980 stratigrafy of part of the lunar near side gspp 1046a

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