Geology topics
D.E. Wilhelms
Publications and source records attributed to D.E. Wilhelms.
Lunar highlands volcanism implications from Luna 20 and Apollo 16
Highlands materials sampled at the Apollo 16 and Luna 20 sites represent units of distinctive morphology that are widespread on the lunar nearside. Samples from the Apollo 16 site represent hilly and furrowed materials of the Descartes highlands and Cayley Formation. Materials were collected by Luna 20 from terrain resembling the Descartes terrain. Most photogeologic interpretations of these units favored volcanic origins, but the samples fail to support this interpretation. Luna 20 soil fragments are mainly glassy microbreccia with lithic inclusions of fine-grained hornfels; less than 3 percent of the fragments have textures of volcanic rocks, and most of these are likely crystalline products of impact melting. Apollo 16 soils formed on ejecta derived from a plutonic anorthosite-norite-troctolite suite. The similarity of Luna 20 soils indicates that these too formed as regolith on ejecta of anorthosite-norite-troctolitc composition. Interpretation of the samples from the two locations now suggests that hilly and furrowed terrains, previously thought to be of volcanic origin, are impact ejecta; in view of the plutonic nature of the source rocks and their extensive fusion and metamorphism, it is likely that the ejecta were derived from multiring basins. At one point, the Apollo 16 site, the Cayley Formation is composed of basin ejecta.
Preliminary geologic map of the Oxia Palus Quadrangle of Mars, Viking Mars 1975 landing site
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Mariner 9 television reconnaissance of Mars and its satellites: Preliminary results
At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark, spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes, are at different levels. The largest crater within the southernmost spot is approximately 100 kilometers wide. The craters apparently were formed by subsidence and resemble terrestrial calderas. The south polar cap has a regular margin, suggesting very flat topography. Two craters outside the cap have frost on their floors; an apparent crater rim within the cap is frost free, indicating preferential loss of frost from elevated ground. If this is so then the curvilinear streaks, which were frost covered in 1969 and are now clear of frost, may be low-relief ridges. Closeup pictures of Phobos and Deimos show that Phobos is about 25 ±5 by 21 ±1 kilometers and Deimos is about 13.5 ± 2 by 12.0 ±0.5 kilometers. Both have irregular shapes and are highly cratered, with some craters showing raised rims. The satellites are dark objects with geometric albedos of 0.05.
Geologic map of the Taruntius Quadrangle of the Moon
The distribution of major physiographic provinces and geologic units of the Tarant ius quadrangle is determined by the five intersecting circular multi-ringed mare basin s. Three basins, i n probable order of decreasing age, are Tran quill itatis , Fecun ditatis , Serenitatis, Nectaris , and Crisiu m . The uplifted ring structures of the basin form terra mountains, peninsulas , and islands, and the depressions between the uplifts are the major deposition sites of post -basin terra and mare material.
Geological provinces of the near side of the moon
Systematic geologic mapping of the near side of the Moon has provided the basis for defining and delineating the major geological provinces of the near side. From the nature of the provinces and their distribution patterns a general historical sequence evolves. Five main surface-shaping periods are recognized: (1) one of intense early impact cratering; (2) another, probably overlapping the first, during which the impact basins were formed; (3) a prolonged period of varied terra volcanism; (4) a short period of mare volcanism that resulted in filling of the multiring basins; and (5) a period of diminishing volcanic activity continuing up to the time of formation of the last ray craters.
Two former faces of the moon
Systematic geologic mapping of the lunar near side has resulted in the assignment of relative ages to most visible features. As a derivative of this work, geologic and artistic interpretations have been combined to produce reconstructions of the Moon's appearance at two significant points in its history. The reconstructions, although generalized, show the Moon (1) as it probably appeared about 3.3 billion years ago after most of the mare materials had accumulated, and (2) about 4.0 billion years ago after formation of the youngest of the large multiringed basins, but prior to appreciable flooding by mare material.
(ORB II-2(25)) Geologic map of Apollo landing site 1, part of Maskelyne DA region southeastern Mare Tranquillitatis
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Summary of lunar stratigraphy - telescopic observations
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(LAC-59) Geologic map of the Mare Vaporum quadrangle of the moon
The Mare Vaporum quadrangle is centrally l ocated on the near side of the Moon, southeast of the craterlike basin of Mare Imbrium . Stratigraphic units and structures peripheral to the basin and rela ted to it domina te the terra of the quadrangle, and one of the maria, S inus Medii , is in a trou g h that is concentric with the basin. The other principal maria, Mare Vaporum a n d Sinu s Aestuum , occupy craterlike basins that apparently antedate the Imbrium basin and developed independently of it. Some stratigraphic units and structures, mostly relatively young , are present that are not related to mare basin.
(LAC-60) Geologic map of the Julius Caesar quadrangle of the moon
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Preliminary geologic map of Ellipse II-2-1 and vicinity
The map area contains landing ellipse II-2-1 and lies near the southern edge of southeastern embayment of Mare Tranquillitatis, a region of typical flat mare and terrain of gently undulating relief and moderate albedo.