apollo 16 preliminary science report

8/8/2019 Apollo 16 Preliminary Science Report

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PHOTOGEOLOGY 29-13

Distribution of Terra Plains

The following patterns of distribution also bear onthe origin of terra-plains deposits: (1)pools are atwidely different elevations, (2)plains tend to beconcentrated in belts peripheral to the conspicuous

ejecta blankets of multi-ring basins, and (3) certainuplands deposits have some characteristics in com-mon with the plains deposits.

Elevation of pools . A wide variation of poolelevations in Cayley Plains exists. A spread of morethan 2 km in Cayley elevations was observed in thearea studied (170 by 140 km shown in fig. 29-14).This variation is in marked contrast to the nearlyuniform elevations of mare surfaces in similarlyrestricted areas.

I0 200-7I0000

98oo

96 0 0-- 7400

920(2 '_E 9000=" [ FIGURE 29-15.-Imbrian terra-plainsmaterials north of Mare

E- 8800 j Frigoris are concentrated in an annulus on the northern8600 r- - side of the Imbrium Basin (Lunar Orbiter IV photo-

8400 L graph M190).8Z00 distance of 300 to 500 krn by a blanket of texturedejecta (refs. 29-29 to 29-31), and beyond that are

8000 I numerous patches of plains-forming material. In78oo figure 29-16, large patches occur near Riccioh Crater;7 600 in and near the Grimaldi Basin; in Darwin Crater and

to the east for 300km; from Vieta Crater to7 4000 1 2 3 4 5 6 7 8 9 10 11 12 Schickard Crater; and beyond to the south andNumb erfpat che s

southeast. Some of these plains near the OrientaleFIGURE 29-14.-Histogram of elevationsof pools of Cayley Basin locally show surface textures (e.g., faint ridges

Formation Plainsshown in figure29-6. and furrows). These textures are of such low reliefthat similar textures in deposits as old as the Imbrium

Areal distribution .-Numerous large patches of the Basin would probably be degraded beyond recogni-Cayley Formation are concentrated in a belt periph- tion. West of the Orientale Basin on the far side, largeeral to the Fra Mauro Formation between Fra Mauro patches of youthful plains-forming material are notCrater on the west and Cayley Crater on the east conspicuous except in Hertzsprung Basin (fig. 29-11).(refs. 29-4 and 29-15). A similar belt of large patches Elsewhere, the area west of the Orientale Basin isof Imbrian terra-plains materials occupies an analo- rugged, heavily cratered terrain. As shown in fig-gous position north of the Imbrium Basin, from ure 29-17, instead of large pools, there are numerousArnold Crater to Volta Crater (fig. 29-15). closely spaced small pools at different elevations

The Orientale Basin is fresher and better preserved commonly filled to the brim with plains material.than the Imbrium Basin. The basin is surrounded to a The appearance is similar to the apparently heavily


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29-14 APOLLO 16 PRELIMINARY SCIENCE REPORT

:_ FIGURE 29-17 .-A_ea 750 t o 1200 km wes t of the weste r n": :_ rim cr est o f the Orie n tale Basin sh owing locall y h eavy

mantling by terra-plains material; for example, just northof the center of the figure (Lunar Orbiter I pho to-graph M 28).

FIGURE 29-16.-Imbrian terra-plains ma terials east of theOrientate Basin. The outlined area near Grimaldi Crate r isshown in figu r e 29-9. The outlined area southwest ofScbickard Crater is shown in figure 29-10 (L unar OrbiterIV photograph M19 0). Schr&li nger Basin

Cr a te re der ramantled ter rain northeast and northwest of Ptolemaeus J P re -I mbrian

Crater in the near side central high lands. / //terra p lai ns

The pre-Imbrian Necta r is Basin also appears t o / / Necta ris radia ls] Neeta risBa sinave remnants of a surr ounding belt of plains-forming j /materials, at least on the south (fig. 29-18). Thesepre-lmbrian plains are far to the south of the basinbeyond a belt with topographic grain radial to thebasin. The grain is caused by the intrinsic ridges ofthe mid-pre-lmbrian Janssen Forma t ion (ejecta of theNectaris Basin, ref. 29-32) and by the "sculpture" of

the Nectaris event. The plains appear to be super-

posed on the sculpture. Beyond the plains is a heavily FIGURE 29-18.-Nec taris Basin an d the area t o the south.cratered terrain with few patches of plains. Pre-lmbrian terra-plains material is peripheral to the area

Possibly r elated uplands deposit s.- Areas of s ub- with radial topographic grain. The plains appea_ to be

dued topography adjacent to the Cayley Plains, in superposed on Nectaris sculpture (Lunar Orbiter IV pho-some cases, are gradational in albedo and topography tograph M52).with plains-forming materials. This has led to theinference that such subdued areas are mantled by the

plains-forming material or related materials(refs. 29-20 to 29-22). One large upland that may be


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PHOTOGEOLOGY 29-15

heavily mantle d by draped, rather than p ool-like, The patch of the Cayley Formation that occupies theCayley materials isthe Kant Plateau -(ref. 29-21). entire floor of Parry Crater shows a profile that can

The Kant Plateau is one of the highest points on best be explained by differential compactionthe near side (ref. 29-33). The plateau rises above (fig. 29-8). The heightened rim flank relative to theadjacent terrain along scarps as high as 2.0 kin, interior of many of the subdued craters could beespecially on its eastern side, and is part of the main explained by the partial draining away of a blanketingmountainous ring, including the Altai Scarp (Rupes flow sheet in intercrater areas while portions of theAltai) to the south , that bounds the Nectaris Basin. sheet are trapped inside the mantled craters. InThe surface of the Kant Plateau is partly smooth and Ptolemaeus Crater, for instance, the subdued craterspartly undulating at distances of 1 to 10 km but are located in the northern two-thirds of the cratergenerally is distinctly smoother than surrounding (ref. 29-20), and it seems possible that Cayley mate-lunar terrain. Locally level surfaces suggest the rials could have flowed toward the southern third,plateau is heavily mantled by materials of the Cayley totally obscuring any preexisting craters there withFormation. At the south end of the plateau, promi- the resulting thicker cover.

nent scarp-bounded lobes of Cayley-like material The domical hills in the Cayley Formation possi-occur (figs. 29-12 and 29-13). bly may be built of lithic fragmental debris, silicate

Another possible lobate form at approximately melt spatter, or viscous silicate flows erupted bythe same distance from the Imbrium Basin occurs degassing or other fluid loss from the Cayley itself,

near Ritchey J and Abulfeda D Craters, 300 km to more or less analogous to the formation of fumarolicthe west-southwest. Both there and at the plateau, mounds on the Bishop ash-flow tuff in Californiathe lobes are roughly south of large clustered craters described by Sheridan (ref. 29-34).elongated radial to the hnbrium Basin. The craters The lobate flow sheets of Cayley-like materialreferred to on the Kant Plateau are Z_llner and

around the Orientale multi-ring basin (figs. 29-9 toKant G (fig. 29-12). 29-11) appear to flow from the textured Orientale

ejecta blanket and Orientale secondary craters. Atleast some such sheets and lobes may represent parts

Interpretation of the Cayley-type flows that became more viscous

The foregoing characteristics can be explained by by addition of extra material from the ballisticthe hypothesis that terra plains-forming deposits are a system into the still-flowing, fluid transport system.facies of ejecta from the impacts that formed The presence of an unusually heavy mantle of

multi-ring basins. This facies must have been trans- Cayley-like material on the Kant Plateau possibly isported and deposited in a distinctly different regime associated with the formation of the Z 611ner andthan the radially ridged, continuous ejecta blankets Kant G Craters (fig. 29-12). The age, clustering, size,such as the Fra Mauro Formation. In the model, the elongation, degree of irregularity in shape, andbasin ejecta segregates into two principal t r ansport distance from the lmbrium Basin of these craters, andregimes, one mainly ballistic and the other highly their similarity with others alined roughly radial tofluid. The terra plains result from deposition of the the lmbrium Basin (Hypatia Crater, 150 km north-fluid Portion, mainly beyond and after deposition of east; the elongate cluster from Andel M C r ater tothe continuous, topographically textured blanket. Andel P Crater approximately 240 km to the west-

This interpretation of the Cayley Formation southwest; and Ritchey Crater and the cluster fromaccounts for its circumbasin distribution and occur- Ritchey J Crater to Abulfeda D Crater approximatelyrence in level pools. Each patch of terra-plains 60 km beyond), suggest that they all may be lmbriummaterial pooled in a local preexisting depression, so secondary-impact craters. If Z_311ner and Kant Gthat the resulting pools have a variety of elevations , Craters impacted on the Kant Plateau at the samedepths, and drainage areas, time that the postulated fluid Cayley debris was

The subdued or ghost craters might be produced passing the area, the sheet of flowing Cayley materialby differential compaction of an initially level cover may have become overloaded with the secondaryas suggested by Howard and Masursky (ref. 29-20), or ejecta. The resulting more viscous flow then mightby an initially draped mantle of fragmental material, have partly moved southeast and southwest off the


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plateau in thick, lobate tongues (figs. 29-12 and chided both solids and drops or shreds of rock melt.29-13), while much of the material was deposited The gas may have been vaporized target, projectile,before it flowed off the plateau, or both.

If the Cayley Formation originated from theImbrium Basin, the material must have segregatedfrom the continuous ejecta now represented by the Conclusions

Fra Mauro Formation. The continuous ejeeta may By the hypothesis discussed earlier , each basin-have traveled primarily on ballistic trajectories to near forming event produced thick plains deposits in a beltits site of deposition and then flowed along the peripheral to the continuous ejecta blanket and mayground as a mobilized debris sheet during deposition have deposited a thinner layer in pools over the entireto produce the radially ridged Fra Mauro deposit. It is Moon. Thus, each patch of terra plains is likely to bepossible that the segregated Cayley material was underlain by a sequence of ftuidized ejecta deposits,transported as a fluid system generally later than and which were derived from most or all multi-ring basinsto greater distances than the F r a Mauro material. This younger than the occupied depression. If the lightfluid or fluidized material pooled in low places, rarely color of the plains results from a high feldsparleaving a conspicuous subduing mantle over adjacent content of the excavated crustal rocks, an explana-terrain. As a partial explanation for the lack of a tion of the absence of exposed pre-Cayley mare rocksconspicuous continuous blanket, the fluid material may be that they are buried or dusted over.

may have been partly channeled into separate tongues The last basin-forming event was Orientale. If theor at least may have been partly channeled into thick dusting of plains materials from the Orientale Basinstreams and thin intervening webs. has a significant thickness on plains throughout the

Although other mechanisms may be possible, the Moon, this could account for the post-Fra Maurohigh fluidity of the transport system that formed the coeval ages for near-side and far-side plains patchesCayley Formation seems to imply that it was gas along the Apollo 16 orbital track determined fromfluidized. The particulate component may have in- crater shapes (part A of this section).

PART C

SMALL-SCALE ANALOGS OF THE CAYLEY FORMATION ANDDESCARTES MOUNTAINS IN IMPACT-ASSOCIATED DEPOSITS

James I4/.Heada

Introduction Cayley Formation

The exploration of the Cayley F ormation and In the central highlands of the Moon, the Cayleymaterial of the Descartes Mountains and an under- Formation f orms locally hummocky but regionallystanding of the origin and evolution of these units flat plains that fill in older highland craters andwere primary objectives of the Apollo 16 lunar intercrater areas. Figure 29-19(a) shows the filledmission. The purpose of this subsection is t o examine craters Dollond B and C, less than 100 km northwestseveral areas associated with impact crater deposits of the Apollo 16 landing site. These plains show anthat show small-scale features similar in morph ology albedo that is intermediate between the maria and theto the regional characteristics of the Cayley and highlands, and the surface generally shows a higherDescartes units shown in the Apollo 16 photography, crater frequency than the maria. The contact between

the plains and surrounding deposits is generally sharpon a regional scale and gradational on a local scale.The:different isolated areas of the plains occur at a

aBeUTelephone Laboratories. wide variety of elevations. The highland materials


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PHOTOGEOLOGY 2% 17

km

FIGURE 29-19.-Analogous r egions o f the Cayley Plains and Aristarchus Crater. (a) Central highlandregion. Cayley Plains fill Dollond B Crater (center), DoUond C Crater (upper left, adjacent toDollond B), and low intercrater areas. The Apollo 16 landing site is in the lower right corner

(portion of Apollo 16 metric camera frame 1955). (b) Analogous region near Aristarchus Crater,showing lineated highlands and plains in low areas. The location of Aristarchus Crater is shown infigure 29-20 (portion of Lunar Orbiter V photograph 205 H3).

surrounding the Cayley Plains usually are in the form with the surrounding units and an apparently higherof old cratered terrain, forming either heavily cra- crater frequency. The surrounding terrain in figuretered plateaus or rims of large old craters (fig. 29-19(b) is plateaulike and contains several large29-19(a)). This terrain is often striated or grooved craters, some of which have been greatly modified.and furrowed by parallel to subparallel lineations that This terrain is regionally grooved and furrowed by

are generally radial to a nearby major multi-ringed parallel lineations radial to a surrounding nearby largebasin (Imbrium Basin in fig. 29-19(a)) but that do not crater (Aristarchus), but the grooves and furrows dotransect the plains. The crater frequency of the not cut the plains. The deposits and associatedhighland regions is generally lower than the fiat structures from Aristarchus (fig. 29-19(b))are there-plains, but this difference isprobablycaused by more fore very similar to those seen in the centralrapid erosion of craters on the topographically more highlands. However, the circular plains deposit inirregular highlandsurfaces, figure 29-19(b) is only 410 m in diameter. The

Certain deposits associated with Aristarchus Cra- diameter of the plains that fill Dollond B (fig.ter show particular similarity to the Cayley Plains and 29-19(a)) is approximately 32 km, more than 75surrounding highlands, both in morphology and in times larger. The Aristarchus structure occurs be-position relative to adjacent impact craters. The tween one and two crater diameters away from thedeposits and structures differ markedly in scale, rim of Aristarchus (fig. 29-20) in an area apparently"however. Figure 29-19(b) illustrates this area and dominated by secondary crater strings, which haveshows two distinct deposits of plains material: one been modified either by subsequent outward sweepfills in the crater at the lower right center, and the of Aristarchus continuous ejecta or by materialother is elongated in a furrow trending northwest- deposited in the same event that produced theward (parallel to the regional structural trend) at the secondary craters. Little evidence exists for anyupper left. These plains deposits are characterized by subsequent event that might have filled the lows anda smooth surface with regionally sharp boundaries formed the plains. The similarity between these


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29-18 A POLLO 16 PRELIMINARY SCIENCE REPORT

FIGUR E 29-20.-Aristarch us Cra ter and Atistarch us Plateauregions. The young crater A tistarchus in the upper leftcenter is 40 km in diameter. The location of the areashown in figure 29-19(b) is indica ted by the arrow(Apollo 15 metric cameraframe 2609).

deposits a nd the Cayley Plains and associated units inthe ce n tral highlands suggests that an impact-relatedorigin should be thoroughly inves tigated for theformation and modification of this terrain. The grossscale differences suggest that cratering on a muchlarger scale than Aristarchus (e.g., the Imbriumimpact) may be the event to which the Cayleydeposits are related.

Materials of t h eDescartes Mountains

The units comprising the hills and uplands fromDescartes Crater north to the region of the Apollo 16landing site include a wide variety of rugged topog-raphy with local relief of several hundred meters(refs. 29-21 and 29-35). Hilly, domed, furrowed, andsubdued subunits have been mapped (ref. 29-35).Particular attention is focused here on the furrowed lab I Isubunit of the Descartes Mountains, which is charac- 0 5kmterized by twisting elongate depressions that rangefrom 1 to 2 km in width. These elongate furrows ordepressi ons tend to be more continuous than the FIGURE 29-21.-Descartes region and M rsting C Crater.other subunits; their trend, while locally variable, (a) Apollo 16 landing area, Descartes region, showing thetends to be parallel or normal to regional lineations grooved and furrowed structures of the rough Descartesupland terrain ( portion of Apollo 16 pan camera frame(fig. 29-21(a)) such as those radial to the Imbrium 4563).


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PHOTOGEOLOGY 29-19

Basin. Individual furrows are often surrounded by twisting depressions median to ridges that trendraised rims , and occasionally two parallel furrows are dominantly concentric to the rim of M /Ssting Cconnected by a short perpendicular furrow in a zigzag Crater. Occasionally, two furrows are connected by a

manner (upper part of fig. 29-21(a)). Similar fur- short, radially trending furrow to produce a zigzagrowed deposits occur in the Zupns Crater r egion, structure. These furrowed structures appear to differ

northwest of the Humorum Basin. from other dunelike structures surrounding MSsting CAn area adjacent to the fresh, young impact crater Crater only in the presence of the furrow. Although

MSsting C (l50 ' S 810 ' W) shows features that are at present it is not clear why the furrowed structuresremarkably similar to the Descartes furrowed units in are locally developed, their similarity to other strut-almost every aspect except scale . The elongate fur- tures surrounding Mbsting C Crater suggests anrows in this area (fig. 29-21(b)) show linear and impact-associated, rather than volcanic, origin. The

dunelike structures may be clots or mounds of ejectathat have been modified by additional ejecta flowsimmediately following their deposition. They mayalso be dunes of material deposited around the craterduring the sweep of ejecta associated with theformation of MSsting C Crater (fig. 29-22). Where

FIGURE 29 -22.-MSsting C C r ater,a pproximately 3.5 km indiame ter. The inse t shows the location of the area shownin figure 29-21(b) (po r tion of Lunar Orbi ter 1II frame113 M).

furrOws occur in the dunelike structures ( fig.29-21(b)), they appear not to have been modified bythe general outward sweep, thus suggesting that they

Ib_ t I may have been formed in the latest stages of or500m subsequent to the M_Ssting C event. In addition, the

FIGURE 29-21.-Concluded. (b) Furrowed dunelike strut- down-range side of several of these structures appearstuxes near MSstingCCrater (portion of LunarOrbiter III to lie just inside an older crater or depression (lowerframe 112 H2). center of fig. 29-21(b)). These relationships suggest


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29-20 APOLLO 16 PRELIMINARY SC IENCE RE PORT

that at least some of the dunelike st r uctures formed they differ radically in scale. The ridges and furrowsat the edge of a depressi on during the MSsting C of M Ssting C Crater average approximately 70 m inevent and then partially collapsed or slid down into width and approximately 200 m in length (fig.the depression, which caused the formation of the 29-21(b)), and those in the Descartes region averagefurrow. Under this hypothesis, the furrows would approximately 2 by 8 km, approximately 30 to 40

originate through the mass wasting or faulting of times larger. The similarity between these depositsimpact-generated deposits, suggests that an impact-related origin, or an originAlthough the deposits associated with MSsting C related to the structural modification of impact-

are similar in morphology to the furrowed units of related deposits, should be thoroughly investigatedthe Descartes region (figs. 29-21(a) and 29-21(b)), for the formation and modification of this terrain.

PART D

DESCARTES HIGHLANDS: POSSIBLE ANALOGS AROUND THE ORIENTALE BASIN

Carroll Ann Hodges a

The Descartes highlands are adjacent to the terra straight walls and V-shaped cross sections, but manyplain on which the Apollo 16 lunar module landed are chains of small coalescent craters. The Stone(fig. 29-23). A variety of volcanic origins was Mountain unit has a rounded, knobby surface,proposed for the highlands before the mission produced by a network of closely spaced, branching,(refs. 29-4, 29-21, and 29-35 to 29-37), but the curved furrows. A steep escarpment marks thereturned samples of the area consist almost contact of the mountain with the plains along theexclusively of nonvolcanic breccias. The breccias northwestern edge. The unit apparently fdls andobtained from Stone Mountain have not been partly buries the rim of Descartes Crater , thusidentified conclusively as sample materials of the suggesting a depositional or constructional origin. InDescartes Mountains (ref. 29-35). A volcanic origin is contrast, the generally south-sloping Smoky Moun-thus not yet precluded (see. 6 of this report), but a tain unit exhibits a smoother, more subdued surfacereview of possible impact-related origins seems to be with broader spacing between furrows; the predom-appropriate. The orbital photography acquired during inant trend of these furrows is northwest. Because ofthe Apollo 16 mission pro vides excellent imagery on these northwest trends, the surface appears grada-which geomorphic interpretations may be based. No tional with pre-lmbrian crater rims to the northwest,obvious local crater is a plausible source of the wilich are furrowed or "sculptured" radially to thematerial, but there may be a relation to either the Imbrium Basin (fig. 29-23(b)).Nectaris or hnbrium Basin. The less degradedOrientale Basin (fig. 29-24) provides a model by Stone Mountain Analogswhich these comparisons can be made (part F of thissection). Two small patches of dunelike ejecta east of the

Orientale Basin (fig. 29-24) are similar morphologi-The Descartes highlands can be subdivided into tally to the Stone Mountain unit (fig. 29-25). These

two major geomorphic units. These units are desig- features apparently were formed by ejecta thatnated in this discussion as the Smoky Mountain flowed outward from the Orientale Basin and(north) unit and Stone M ountain (south) unit (fig. crowded against preexisting crater walls. The resulting29-23(b)). Both are characterized by furrows or crenulate ridges have been termed "decelerationgrooves of various dimensions. Some furrows have dunes" (ref. 29-31), and their textural similarity to

the materials of the Descartes Mountains has been

aU.S. Geol ogical Survey. discussed by Trask and McCauley (ref. 29-37). The


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PHOTOGEOLOGY 29-21

k

FIGURE 29-23.-Th e Descartesh ighland sregion . (a) Photograph icbase f or the accomp anyingm ap ofthe Desca rtesregio n (Apollo 16 mapping camera frames 0439 and 0440). (b) Sket ch map of thesame area; furrows and approximate outline of th e two units of the Descar tes highlands areindicated. Plains of t he Cayiey Formation are shaded; craters a xe shown by hachures.Northwest- southeastRend of t he furrows on t he western side of the map area i s radial to theImbrium Basin.

Stone Mountain uni t is adjacent to a west -facingescarpment of the Kan t Plateau (part of the Nectarisring structure, fig. 29-26), suggesting that this unitmay have been similarly derived from the Imbrium

Basin to the northwest. Deceleration dunes from theNectaris Basin are unlikely, because ejecta from thebasin would have crowded against east-facingescarpments. The apparent gradation of the materials

in Descartes Crater with lineated terrain immediatelyto the west (fig. 29-23) supports an Imbrium-ejectahypothesis. This terrain has a ridged and braidedtexture radial to the Imbrium Basin and resembles the

Fra Mauro Formation (Imbrium ejecta) (fig. 29-27).

However, several problems remain unexplained bythis hypothesis.

(1) Whereas similar dunelike deposits occur atseveral places around the Orientale Basin, the StoneMountain unit appears unique around the ImbriumBasin, despite the prevalence of scarps against whichFIGURE 29-24.-The Orien tale Basin. Areas outlined are

shown separately: areaA is shown in figure 29-25(a); ejecta could have accumulated, such as the southernareaB is shown in figure29-25(b); and area C i s shown in walls of Ptolemaeus, Albategnius, Alphonsus, andfigure 29-28 (Lunar Orbiter IV mosaic), other craters (fig. 29-26).


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I FIGURE 29-26:-Centra l highlands, showing Nectaris Basinring structures, sglected craters, and area of Imbriumsculpture. The location of figure 29-23 (Descartes region)is outlined (Lunar Orbiter IV mosaic).

(a)

FIGURE 29-25.-Ejecta dunes in preexisting craters east ofthe Orientale Basin. Furrows between dunes are indicated.

These locat ions are shown in figu r e 29-24. (a) Ejecta dunesin Rocca Crater. (b) Ejecta dunes in Darwin Crater. (Theenlargements are from Luna r Orbiter IV p hotographH168). FIGURE 29-27.-Type locality of the Fra Mauro Formation.

Arrow indicates the direction from Imbrium Basin. Thearea shown is approximately 70km across (LunarOrbiter IV photograph H120) .


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PHOTOGEOLOGY 29-23

(2) The Descartes area is considerably far ther from highlands at the landing site. Despite the similarities,the Imbrinm Basin (1000 km from the Apennine however, some observations seem inconsistent withring) than are the deceleration dunes from the an analogous origin for the Descartes materials.Orientale Basin (300 km from the Cordillera ring). (1) The Stone Mountain unit appears to be a

(3) Within Descartes Crater are prominent concen- unique occurrence and is outside the third ring of

tric furrows (fig. 29-23), which conflict with the Nectaris. At the Orientale Basin, however, thedeposition hypothesis. Descartes-like materials are virtually ubiquitous

(4) If the Stone Mountain unit is Imbrium ejecta, between the second and third rings.it predates the Cayley material, which is superposed (2) Superposifion of the unit on Descartes Crateron Imbrium sculpture. However , crater frequencies indicates that, unlike the Orientale analog, preexistingon Stone Mountain appear lower than those of the landforms were not obliterated.Cayley Formation, suggesting relative ages that are (3) The low density of superposed craters on Stonethe reverse of those obtained by superposition Mountain suggests a p ost-Nectarisage.relationships. A possible explanation is the observa-

tion that crater populations on Stone M ountain have Smoky Mountain Unit

been reduced by mass wasting on the steep slopes. Possible nonvolcanic interpretations of the SmokyA second analog at the Orientale Basin suggests as Mountain unit include (1) pre-Imbrian crustal rock or

an alternative that there is a possible relation of the Nectaris ejecta, sculptured by secondary cratering orStone Mountain unit to the nearby pre-Imbrian faulting radial to the Imbrium basin, or (2) ImbriumNectaris Basin. The hummocky, furrowed terrain ejecta. The trend of the furrows is predominantlybetween the Rook and Cordillera Mountain rings of northwest, radial to the Imbrium Basin, suggestingthe Orientale Basin (fig. 29-28) resembles the Stone Imbrium sculpture. Smooth, broad surfaces are more

prominent than in the Stone Mountain unit, andcrater densities appear slightly higher (similar to thoseon the plains). The close spatial association with theNectaris Basin implies that the sculptured materialsmight include Nectaris ejecta.

Alternatively, the Smoky Mountain unit may beradially textured Imbrium ejecta. This possibility is

suggested by a gradational, although highly discontin-uous, relationship with lineated deposits in the norththat resemble the Fra Mauro Formation. Ridgeddeposits which are also similar in appearance to theFra Mauro Formation occur farther south, west ofDescartes Crater (fig. 29-23). The Smoky Mountainunit , however, does not itself appear ridged andbraided as does the Fra Mauro Formation (fig. 29-27)and similar deposits.

FIGURE 29-28. -Hummocky terrain be tweenthe second andthird rings of the OrientaleBasin.Furrows are indicated.Mare materials fl ood the hummocky terrain on the north Conclusion(Lunar Orbiter 1VphotogIaph H181).

These analogs, although not entirely satisfactory,

Mountain unit; the materials appear to be localized offer reasonable alternatives to the volcanic interpre-mainly in the inter-ring depression. Preexisting tation of the Descartes highlands. Reconsideration oflandforms are not recognizable and thus must have this complex terrain, prompted by the preliminarybeen obliterated during basin formation. Where later results of the Apollo 16 mission, will lead to themare materials have fiUed low areas within this revision of some theories on lunar volcanism and alsoterrain, the morphologic relations are slightly similar to a better understanding of the landforms caused byto those of the Cayley Plains and the Descartes the formation of multi-ring basins.


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PART E

ORIENTALE BASIN DEPOSITS (RICCIOLI AREA) IN APOLLO 16EARTHSHINE PHOTOGRAPHY

D. D. Lloyd a and J . 14/.Head a

Photography of Orientale Basin deposits was earthshine photographs obtained on the Apollo 16obtained under earthshine illumination conditions on mission as well as Lunar Orbiter IV coverage of thethe Apollo 16 mission. Although the quality of these same area are shown in figure 29-30.photographs is less than that obtainable in sunshine, The region between Riccioli Crater and thethese regions are in the dark during Apollo missions Orientale Basin is characterized by g_ooved, fur-because of the locations of Apollo landing sites, rowed, and braided terrain that generally has a linearPhotography of these regions under different lighting aspect radial or subradial to the Orientale Basin (fig.geometry and from different viewpoints is therefore a 29-31). These units are related to the gigantic ejectauseful addition to previous photographic data. blanket deposited at the time the Orientale Basin

Oblique photography was obtained of Riccioli Crater originated. Riccioli Crater existed before this origin,and adjacent areas, which lie northeast of the and the presence of Riccioli Crater appears to haveOrientale Basin. modified the regional characteristics of the ejecta

A Nikon 35-ram camera with an f /1.2 lens was blanket in this local area. In particular, the outer edgeused. The photographs were obtained at 122:39 of the radially patterned ejecta blanket (fig. 29-31) isground elapsed time with an exposure time of 1 /8 sec indented toward the Orientale Basin as if the presenceunder lighting conditions of approximately 15 from of Riccioli Crater may have obstructed the outwardthe earthshine terminator. The location of these flow of material.

photographs is shown in figure 29-29. The two The photograph of the northern half of RiccioliCrater (fig. 29-30(b)) shows the northeastern rim of

L0 the crater enhanced in brightness by the viewingdirection.eve ralmallratersnheinne rall show

,_- '_ "_._,_ _ high brightness characteristics of zero-phase viewing

5 ____ (here in earthshine), tn the oblique earth shine and in__"__' _-_ _ . the Lunar Orb iter photograph, there is a distinct

z

i_ __'_J_" :_:" impression of material preferentially piledupor

0 _- _ deposited along the northeast crater wall. A distinc-.,,__ tive aspect of this material is that the structures are_ _ _ oriented in a direction generally parallel to the crater

" wall in this area, but normal to the general radial

5 structure of the Orientale blanket. This observationhas led to the suggestion that these linear structuresmight be "deceleration dunes" (ref. 29-31); that is,

185 8O 15 10 65 60 dunes deposited when the outward flow of materialLongitude ,degW was locally slowed by the interference of the Riccioli

Crater wall to such an extent that it largely ceasedFIGURE 29-29.-Location of two earthshine photographs flowing radially at this point and was deposited in

(AS16-127-20018and 20019) obtained on the Apollo 16 transverse dunes. This theory also would explain themission, regional embayment in the outer edge of the distinct

radial structures (fig. 29-31), because much of thematerial would have been trapped within Riccioli

aBellTelephone Laboratories. Crater. It seems clear, however, that at least some


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PHOTOGEOLOGY 29-25

FIGURE 29-30. -Apollo 16 earthshine photography compared to Lunar Orbiter IV coverage.(a) Lunar Orbiter IV photograph H169. (b) Earthshine photograph looking west a t Ricciofi Cra tershowing north half of Riccioll and area east of Ricciofi, including Riccioli G Crater(AS16-127-20019). (c)Earthshine photograph showing craters east of Ricciol i Cra ter, includingRiccioli G and Lohrmann B Craters (AS16-127-20018).


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29-26 APO LLO 16 PRELIMINA RY SCIENCE REPO RT

material surmounted the wall and was deposited tothe northeast (fig. 29-30(a)).

An alternative possibility for these transverseridges is that they may represent slumping of materialback down the crater wall after being piled up againstthe wall of Riccioli Crater during the ejection ofOrientale material . This hypothesis would differ fromthe deceleration dune explanation in the formationmechanism of the deposit structur e, not in thematerial of the deposit. R. Eggleton (personal com-munica tion) has pointed out parts of the materials ofthe Descartes Mountains and associa ted deposits thatmay have originated as a result of major slumping andfaul ting, rather than from constructional volcanism.Some of the structures associated with and formingthese transverse ridges in Riccioli Crater show markedmorphologic and scale similarities to structures seenin the Descartes material. (In particular, see the area

indicated by the arrow in fig. 29-30(a).) The possi-bility that morphologies such as those seen in RiccioliCrater and similar depos its could have originated

through slumping and down-faulting of depositsassociated with major basins should be seriouslyconsidered.

i I0 250

Approximatecale, km

FIGURE 29-31. -Regional embaymen t in the outer edge ofthe distinct radial structures in the Orientate Basin nearRiceioli C r ater.


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PHOTOGEOLOGY 29-27

PART F

REINTERPRETATIONS OF THE NORTHERN NECTARtS BASIN

Don E . Wilhelms a

Geologic units of the Nectaris Basin rim have been multiple ring segments produced during basin forma-interpreted as partly impact and partly volcanic in tion. At both the Nectaris and Orientale Basins (fig.origin (refs. 29-4 , 29-21, 29-35 , 29-38, and 29-39). 29-33), the rings are composed of massifs of variousAn exclusively volcanic origin was proposed for the heights and degrees of ruggedness. Dashed lines onmaterial in the vicinity of the Apollo 16 landing site, figure 29-32 show the approximate position of theslightly northwest of the Nectaris Basin (ref. 29-36). Nectaris rings. The inner ring bounds Mare NectarisIn view of the dominance of breccia and the paucity itself, as the inner Rook Mountains ring would boundof volcanic material in the returned Apollo 16 Mare Orientale if post-Orientale lavas had filled thesamples, it now seems appropriate to reevaluate this basin to a higher level. The second Nectaris ringpart of the Moon to test whether the geology of the corresponds to , though is less conspicuous than, the

units mapped to date can be reconciled with an ring of massifs formed by the outer part of the Rookimpac t origin. Therefore, photogeologic analysis was Mountains at Orientale. The third ring at Nectarisattempted on a strip of Apollo 16 metric photo- (Altai-Kant-Censorinus) corresponds to the Cordilleragraphs; the superior quality and stereographic prop- ring around the Orientale Basin.erties of the photography permit this reevaluation The second major unit related to the Nectaris(fig. 29-32). Geologic contacts, as redrawn, closely Basin, material of small peaks, was not recognizedresemble those of the earlier maps cited, but some previously as a separate photogeologic unit (fig.differences result because of improved photographic 29-34). Parts of it were assigned to various terra unitsquality and a conscious attempt to test fully the interpreted as basin-related material and other partsimpact hypothesis, to hilly and pitted units interpreted as probable

For the purpose of this study, an area including volcanic material. The Apollo 16 metric photographsthe Nectaris Basin rim is compared with an analogous show that the pattern of the small peaks resemblesarea of a younger basin of similar size, Orientale (fig. the less rugged parts of the Orientale rings. At each

29-33), which is doubtless of impact origin. A sketch basin, the small peaks appear basically the same as themap and a description of the major impact-produced more conspicuous massifs, but are broken intounits in and around the Orientale Basin provide a smaller pieces.useful comparison (ref. 29-26). Materials of the two The third unit, hummocky material (fig. 29-35),basins appear to be similar in surface properties and has been variously interpreted; Elston (ref. 29-39)distribution patterns; the differences observed can be suggested two possibilities, volcanic or basin-relatedascribed to the greater age, state of degradation, and material. The Apollo 16 photographs con vincinglylava fill of the Nectaris Basin. However, some favor the second interpretation. The unit resembleslandforms, including the hilly (sou thern) unit of the the sharply humm ocky material that occurs ma inlyDescartes Mountains (ref. 29-35), are difficult to fit between the Rook and Cordillera rings of Orientaleinto a pure impa ct model. Basin and in radial troughs on and beyond Montes

The comparison with the Orientale Basin suggests Cordillera. Hummo cky material at Nectaris occursthat three major units are part of the impact also mainly between the second and third basin rings,stratigraphic sequence of the Nectaris Basin. As in a radial trough west of Lubbock D Crater, and insuggested by most workers, the first unit, material of patches beyond the third ring . The origin of thismountains (fig . 29-34), probably represents uplifted material remains uncertain; it may be basin, ejecta,

bedrock fractured during basin formation, or slumpmaterial, but it almost certainly is related to the

aU.S. Geological Survey. formation ot"the Nectaris Basin.


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Explana tion

Mater ia lsyoung er Crate rmaterial Ma remateria l Lightp lain s Imb rium -influencedthan Ne c ta risBas in ma teria l ma terial

Mantlemater ia lMa te ria lsre lated

toNe ctarisBasi n _ _

Materia lof Material of Hu mmockymo un tains s mallpeaks mater ial

.... O

Basinring structures Buriedcraterrim crest

FIGURE 29-32. -Geo|ogic ma po f the n o rth ern part o f the Ne cta ris Bas in.

Around the Nectaris Basin, as nearly everywhere sions and the fact that this type of terrain seems towithin the terra, there are large areas of undulatory blanket some areas such as that south of the Apollomaterial of rather characterless appearance and uncer- 16 landing site where material of the Descartesrain age. Many of the Orientale landforms, if suffi- Mountains drapes over Descartes Crater (refs. 29-4,ciently degraded by meteorite bombardment and 29-21, 29-35, and 29-37). As concluded earlier from

mass wasting, might resemble this circum-Nectaris telescopic observation (ref. 29-38), basin-related gene-unit. sis is a reasonable alternative for much of the terrain

West of the Nectaris Basin, small pits and grooves because it is near the Nectaris Basin and becausedominate the landscape, including the Descartes many of its landforms appear to be allied to ImbriumHighlands (fig. 29-36). Previously, a volcanic origin sculpture (part D of this section). In a broad belt westseemed best to explain the mix of hills and depres- of the Apollo 16 landing site, the Imbrium sculpture,


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PHOTOGEOLOGY 29- 29

FIGURE 29 -33. -Orientale Basin (Lun ar Orbit er IV mosaic),

trending radially to the Imbrium Basin, is seen inApollo 16 photographs to consist of pits or grooves.The Imbrium sculpture is commonly interpreted asfractures (ref. 29-40 and part G of this section), butthese pits and grooves lend support to the early FIGURE 29 -34.-M aterial of mountains and small peaks ininterpretation (ref . 29-4 1)that sculpture results from the Nectaris Basin. lsidor u s Crater is 4 0 km across ,gouging by secondary impacts of ejecta from the Typic al broad massifs of t he Nectaris inner ring adjoinsiflor uscrater on the wes t and sou th; typical small peaksImbrium Basin Hence, sculptured areas, including the are to the no r th and northw est (Apollo 16 metric cameraDescartes material, are interpreted as Imbrium- frame0148).in fluenced terrain (fig. 29-32). It should be stressedthat, a t this great d istance fi 3m Mare Imbrium. the ors that are sharper than those west of the basin. Asecondary craters and gouges considered for these unitsto the amou n t of impactin_ gular craters that do notthem; hence, only a small am sin secondaries (refs. 29-4material should be mixed witt,In addition to the northwest _ the one certain lunarDescartes material south of th s material in this regiondoes have some northeast-tre_ be basin ejecta (part B ofare not radial to Mare Im reworked erosional debrisDescartes Crater, and appea _rigins that have been longyoung population of superp , the volcanic origin of thethis section) A possible non_ ne of the light plains arethese observations is that :d Nectaris ring as is theBasin ejecta which was modif tale Basin, as if light plains

valent lavas.gouging and faulting that de_ :t of the nonmare materialcraters. A sequence of impact [explain the Descartes materi_ em Nectaris Basin rim can

tartes Crater, formation of tion of impact basins. Thisswamping of Descartes Crater i ed only for some irregularthe Imbrium Basin and pitti_ a of Mare Nectaris and forfaulting along a northeast-soul I : Descartes material. If theImbrian cratering. The bulk o! have been sampled and to

S" iwould then be Nectans Bam ni extensive hill and crater-.The Imbrium-influenced u! of lmbrian or younger age

taris Basin (fig 29-32) refer _tu _u_t_u _t_ u_ p_uouu_y uu_ ,UL _a_t u_the lunar terra


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29-30 APOL LO 16 PRELIM INARY SC IENCE REPORT

F IGURE 29-3 5.-Humm ocky material in th e Nee tar is Ba sin. G utenb erg G Crater is 3 0 km across.Typical hummocky ma ter ial is shown in mo st of the figure and i s best developed in the troughextending nor th of Gute nberg G Crater (s tereopair, A pollo 16 met r ic camera frames 1641 and1639).


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PHOTOGEOLOGY 29-31

PART G

STRUCTURAL ASPECTS OF IMBRIUM SCULPTURE

David H . Scott a

Apollo 16 metric photographs taken at low to high on the floor of Albategnius Crater are shown well onSun angles (from approximately 7 to 40) provide Apollo 16 metric camera frames 0448 and 0449the first stereographic coverage of the distinctive adjacent to figure 29-37. In the area of figure 29-37landforms collectively referred to as "Imbrium 1 (best seen at higher Sun angles as in Apollo 16 metricsculpture" (refs. 29-40 and 29-41). The sculpture camera frames 2803 and 2804), grabenlike, rimless,consists of a series of nearly linear ridges and troughs linear furrows grade into arcuate rimmed depressionsextending radially outward for more than 1000 km resembling highly coalescent crater chairis. Thesefrom the rim of the Imbrium Basin. The sculpture is latter characteristics are not defin itive and mayparticularly well developed in the highlands south- reflect either a volcano-tectonic or secondary-impactwest of the basin, where individual segments have crater origin.

lengths measured in tens of kilometers. The origin of Several topographic characteristics supporting anthe ridges and troughs, whether by deposition and endogenetic origin for the larger elements of Imbriumimpact scoring by fluidized clouds of ejecta from the sculpture are shown in figure 29-38. The wide,Imbrium Basin or by faulting and volcanism during prominent depression in the upper right corner of theand subsequent to basin formation, is controversial, photograph extends across the entire rim and wall ofSimilar appearing features occur around other large Ptolemaeus Crater on the side nearest the Imbriumbasins on both the near and far sides of the Moon;thus, information leading to a better interpretation oflmbrium sculpture has significance throughout theMoon.

Studies of Apollo 16 stereographic photographs inthe vicinity of the large craters Albategnius andHipparchus .(fig. 29-37) show that some troughs haverelatively sharp rims or edges, whereas others aremoderately to highly subdued. In this respect,variations in morphology of the troughs are probablyanalogous to some of the criteria used for the ageclassification of impact craters (ref. 29-42). On thisbasis, the sharpest appearing troughs may be as youngas late Imbrian in age. Some may have volcano-tectonic origins and th us may be younger than similarappearing features formed by impact, if endogeneticprocesses produce forms with an inherently oldappearance. However, most of the troughs seem to beolder than plains material, and their buried outlines

au.s. Geol ogica lSur vey. FIGURE 29-37.- lmbrium scu lpture between Alba tegrdus1Both "Imbrium" and "Imb r ian" have been applied b y Cra ter (lower left) and Hipparchus Crater (top).

var ious autho r s to desc ri bethe sculptu r e. Imbrium is pre- Prog r ession in degradation of furrows is shown by: 1,letted because it shows association with the Imbrium Basin sharp r immed; 2, mode r ately subdued; 3, highly subduedr atherthan the lmb r ian Period. (north toward top, Apollo 16 met r iccamera frame0168).


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Formation. In figures 29-37 and 29-38, the absenceof randomly oriented, overlapping crater clusters is incontrast to the patterns of secondary craters usuallyobserved around large craters.

In figure 29-39, a series of elongate hills forms alinear ridge extending approximately 100 km alongthe east side of Fra Mauro Crater. The ridge is radialto the Imbrinm Basin (approximately 500 km to thenorth) and parallels Rima Parry, a large linear rillepresumably of structural origin. Toward the south,the ridge of hills grades into typically sculpturedtopography. Smaller, isolated, oval-shaped hillsproject above the mare material to the east. All thesehills resemble constructional landforms, probablyformed by a combination of faulting and volcanism.A similar origin is suggested for Imbrium sculpture inthis region.

Evidence indicative of the mode of origin ofImbrium sculpture is summarized as follows.Evidence of a volcano-tectonic mode of origin isfavored by (1) wide variation in relative age of partsof the sculpture, (2) furrows without rims, (3)

FIGURE 29-38. -Sculptured terrain around west side of absence of ballistic shielding, (4) asymmetry ofPtolemaeus Crater (right center). 1, large depression sculpture, (5) absence of randomly oriented clusters,extending across rim and wail of Ptolemaeus; 2, trough and (6) association with other features of structuralwith prominent eastern wall; 3, furrow with high rims; 4,smooth, lineated texture (north toward top, Apollo 16metric cameraf r ame 2814).

Basin. From the figure, no evidence of the rimshielding the wall against missile gouging is

detectable, such as is noted in the disposition ofsecondary crater clusters around large, young,primary-impact craters such as Tycho Crater(ref. 29-43). In the lower right corner of the figure,one side of a large trough appears to be much higherand better defined than the other. This type ofasymmetry is more suggestive of a structural originthan gouging and scoring by impact ejecta. In thisphotograph, as well as in several others, some of thefurrows have conspicuous rims, more readilyexplained by high-velocity, surface-grazing impactsthan by tectonism. However, similar r immed furrowsfarther to the south in the vicinity of Airy andDelaunay Craters are associated with lobate, f lowlikematerials and may be of volcanic origin.

Toward the lower left corner of figure 29-38, aFIGUR E 29-39. -Area ar ound Fra M anroCrater (left center).

continuous gradation is noted between coarse 1, ridge-forminghills; 2 , Rima Parry; 3 , typical sculptu resculpture patterns and finely lineated materials, 4, elongate hills surrounded by mare material (northwhich elsewhere have been mapped as the Fra Mauro toward top, Apollo 16 metric camera frame 1418).


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PHOTOGEOLOGY 29-33

origin. An origin by ejecta scoring and deposition is power function of explosive energy (ref. 29-44). Thefavored by the gradational ejecta with a Fra application of this relationship to energy estimatesMauro-type texture. Features that are ambiguous as required to produce the Imbrium Basin indicates thatto mode of origin are furrows made up of coalesced radial fractures produced by the lmbrium impactcrater chains and prominent rims on furrows, might we

apollo 16 preliminary science report

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