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Don E. Wilhelms

Publications and source records attributed to Don E. Wilhelms.

10 recordsLinked to original sources
USGS2007

Geologic Map of Part of the Western Hellas Planitia, Mars

Introduction Rock units were deposited on Mars by meteorite impact, volcanism, wind, flowing water, standing water, and ice, acting separately or in concert. Hellas Planitia, the deepest tract on Mars, is a broad depression lying within the high-rimmed, approximately 2,300-km-wide Hellas impact basin. The basin and the planitia are centered about 250 km east of the southeast corner of the map area. Like other stratigraphy-based planetary mapping (Wilhelms, 1990), we suggest the most likely origins for age relations and morphologies visible in the map area.

Scientific Investigations Map↗
USGS1987

The geologic history of the Moon

More than two decades of study have established the major features of lunar geologic style and history. The most numerous and significant landforms belong to a size-morphology series of simple craters, complex craters, and ringed basins that were formed by impacts. Each crater and basin is the source of primary ejecta and secondary craters that, collectively, cover the entire terra. The largest impacts thinned, weakened, and redistributed feldspathic terracrustal material averaging about 75 km in thickness. Relatively small volumes of basalt, generated by partial remelting of mantle material, were erupted through the thin subbasin and subcrater crust to form the maria that cover 16 percent of the lunar surface. Tectonism has modified the various stratigraphic deposits relatively little; most structures are confined to basins and large craters. This general geologic style, basically simple though complex in detail, has persisted longer than 4 aeons (1 aeon = 10 9 yr). Impacts began to leave a visible record about 4.2 aeons ago, after the crust and mantle had differentiated and the crust had solidified. At least 30 basins and 100 times that many craters larger than 30 km in diameter were formed before a massive impact created the Nectaris basin about 3.92 aeons ago. Impacts continued during the ensuing Nectarian Period at a lesser rate, whereas volcanism left more traces than during pre-Nectarian time. The latest basin-forming impacts created the giant and still-conspicuous Imbrium and Orientale basins during the Early Imbrian Epoch, between 3.85 and 3.80 aeons ago. The rate of crater-forming impacts continued to decline during the Imbrian Period. Beginning in the Late Imbrian Epoch, mare-basalt flows remained exposed because they were no longer obscured by many large impacts. The Eratosthenian Period (3.2-1.1 aeons ago) and the Copernican Period (1.1 aeons ago to present) were times of lesser volcanism and a still lower, probably constant impact rate. Copernican impacts created craters whose surfaces have remained brighter and topographically crisper than those of the more ancient lunar features.

Professional Paper↗
USGS1973

Stratigraphic studies: Part D: geologic map of the northern Crisium region

Apollo 17 metric photographs (fig. 29-26) provide the best available coverage for geologic interpretation of northern Mare Crisium and the northern Crisium basin. The area was covered previously by low-resolution telescopic and Lunar Orbiter IV photographs and by oblique, high-illumination, or low-resolution photographs from earlier Apollo missions. One region in particular, between Alhazen Crater and longitude 66° E, had previously been covered very poorly. The Apollo 17 photographs provide excellent monoscopic (fig. 29-26) as well as stereoscopic viewing because of the favorably low Sun illuminations (15° to 49°). These new photographic data allow the geology of the basin, the mare, and other nearby terrains to be reevaluated. This reexamination together with data from continuing Moon-wide photogeologic studies and analyses of returned rocks from Apollo landing sites, has produced a simple evolutionary picture of the region, expressed by fewer map units and explained by fewer basic processes than previously thought necessary (refs. 29-35 and 29-45 to 29-48).

Book chapter↗
USGS1972

Orbital-science investigation: Part J: preliminary geologic map of the region around the candidate Proclus Apollo landing site

The Proclus Crater region was mapped to test the value, for photogeologic mapping purposes, of Apollo 15 metric photographs and to estimate the scientific value of the area as a potential landing site. A metric photographic frame (fig. 25-67) serves as a base for a map of the region around the Proclus Crater (fig. 25-68), and adjacent frames were overlapped with the base frame to provide stereographic images. The excellent stereocoverage allows easy simultaneous observation of topography and albedo. The large forward overlap and the extensive areal photographic coverage provide the best photogeologic data available to date. Brief study has already refined earlier interpretations of the area (refs. 25-7 and 25-32). Although volcanic units have been shown to be extensive in this region, mass wasting apparently has been more important than volcanism in shaping terra landforms.

Book chapter↗
USGS1972

Photogeology: Part F: reinterpretations of the northern Nectaris Basin

Geologic units of the Nectaris Basin rim have been interpreted as partly impact and partly volcanic in origin (refs. 29-4, 29-21, 29-35, 29-38, and 29-39). An exclusively volcanic origin was proposed for the material in the vicinity of the Apollo 16 landing site, slightly northwest of the Nectaris Basin (ref. 29-36). In view of the dominance of breccia and the paucity of volcanic material in the returned Apollo 16 samples, it now seems appropriate to reevaluate this part of the Moon to test whether the geology of the units mapped to date can be reconciled with an impact origin. Therefore, photogeologic analysis was attempted on a strip of Apollo 16 metric photographs; the superior quality and stereographic properties of the photography permit this reevaluation (fig. 29-32). Geologic contacts, as redrawn, closely resemble those of the earlier maps cited, but some differences result because of improved photographic quality and a conscious attempt to test fully the impact hypothesis.

Book chapter↗