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Geology topics

J.F. McCauley

Publications and source records attributed to J.F. McCauley.

At least 19 recordsLinked to original sources
USGS2012

Eolian features in the Western Desert of Egypt and some applications to Mars

Relations of landform types to wind regimes, bedrock composition, sediment supply, and topography are shown by field studies and satellite photographs of the Western Desert of Egypt. This desert, which lies at the core of the largest hyperarid region on earth, provides analogs of Martian wind-formed features. These include sand dunes, alternating light and dark streaks, knob ‘shadows,’ and yardangs. Surface particles have been segregated by wind into deposits (dunes, sand sheets, and light streaks) that can be differentiated by their grain size distributions, surface shapes, and colors. Throughgoing sand of mostly fine to medium grain size is migrating southward in longitudinal dune belts and barchan chains whose long axes lie parallel to the prevailing northerly winds, but topographic variations such as scarps and depressions strongly influence the zones of deposition and dune morphology. Sand from the longitudinal dunes on the plains is commonly redistributed into barchans in the depressions. These barchans are generally simple crescents that are morphologically similar to many of the dunes seen on Viking orbiter pictures of the north polar sand sea on mars. Light streaks are depositional features consisting of dune belts and elongate sheets of coarse to medium sand and granules. Intervening dark streaks are erosional features consisting of strips of desert-varnished bedrock and lag gravel surfaces exposed between the sand deposits. The shape of both light and dark streaks is controlled by wind flow around topographic highs. Dark zones (shadows) in the lee of mountains, hills, and knobs are erosional products from the topographic highs; they change shape only in response to movement of the adjacent lighter-colored sand deposits. Streamlined yardangs carved in crystalline limestone constitute one of the largest yardang fields on earth. Yardangs occur also in sandstone of the Nubian Series and in lacustrine sediments. The variables that affect the patterns of wind erosion and deposition in the Western Desert are topographic effects on wind velocities and directions, resistance of the bedrock, sand supply, and climatic change with time; vegetation is essentially absent and is not a controlling factor.

Journal of Geophysical Research Solid Earth↗
USGS1997

The use of multifrequency and polarimetric SIR-C/X-SAR data in geologic studies of Bir Safsaf, Egypt

Bir Safsaf, within the hyperarid 'core' of the Sahara in the Western Desert of Egypt, was recognized following the SIR-A and SIR-B missions in the 1980s as one of the key localities in northeast Africa, where penetration of dry sand by radar signals delineates previously unknown, sand-buried paleodrainage valleys ('radar-rivers') of middle Tertiary to Quaternary age. The Bir Safsaf area was targeted as a focal point for further research in sand penetration and geologic mapping using the multifrequency and polarimetric SIR-C/X-SAR sensors. Analysis of the SIR-C/X-SAR data from Bir Safsaf provides important new information on the roles of multiple SAR frequency and polarimetry in portraying specific types of geologic units, materials, and structures mostly hidden from view on the ground and on Landsat TM images by a relatively thin, but extensive blanket of blow sand. Basement rock units (granitoids and gneisses) and the fractures associated with them at Bir Safsaf are shown here for the first time to be clearly delineated using C- and L-band SAR images. The detectability of most geologic features is dependent primarily on radar frequency, as shown for wind erosion patterns in bedrock at X-band (3 cm wavelength), and for geologic units and sand and clay-filled fractures in weathered crystal-line basement rocks at C-band (6 cm) and L-band (24 cm). By contrast, Quaternary paleodrainage channels are detectable at all three radar frequencies owing, among other things, to an usually thin cover of blow sand. The SIR-C/X-SAR data investigated to date enable us to make specific recommendations about the utility of certain radar sensor configurations for geologic and paleoenvironmental reconnaissance in desert regions.Analysis of the shuttle imaging radar-C/X-synthetic aperture radar (SIR-C/X-SAR) data from Bir Safsaf provides important new information on the roles of multiple SAR frequency and polarimetry in portraying specific types of geologic units, materials, and structures mostly hidden from view on the ground and on Landsat images by a relatively thin, but extensive blanket of blow sand. Basement rock units and associated fractures at the Bir Safsaf are clearly delineated using C- and L-band SAR images. The detectability of most geologic features depend primarily on radar frequency. The SIR-C/X-SAR data also provide recommendations about the utility of certain radar configurations for geologic and paleoenvironmental reconnaissance in deserts.

Remote Sensing of Environment↗
USGS1993

Surficial geology of the Safsaf region, south-central Egypt, derived from remote-sensing and field data

We used a decorrelation-stretched image of Landsat Thematic Mapper (TM) Bands 1, 4, and 7 and field data to map and describe the main surficial units in the hyperarid Safsaf region in south-central Egypt. We show that the near-infrared bands on Landsat TM, which are sensitive to very subtle changes in mineralogy common to arid regions, significantly improve the geologist's capability to discriminate geologic units in desert regions. These data also provide the spatial and spectral information necessary to determine the migration patterns and provenance of eolian materials. The Safsaf area was the focus of our post flight field studies using Shuttle Imaging Radar (SIR) data following the discovery of buried paleochannels in North Africa. Most of the channels discernible on SIR images are not expressed in TM data, but traces of a few channels are present in both the SIR and the TM data within the Wadi Safsaf area. Here we present a detailed digital examination of the SIR and the TM-band reflectance and reflectance-ratio data at three locations of the more obvious surface expressions of the buried channels. Our results indicate that the TM expressions of the channels are not purely topographic but are more compositional in nature. Two possibilities may account for the TM expressions of the buried channels: 1) concentrations of windblown, iron-rich materials that accumulated along subtle curvilinear topograpohic traps, or 2) curvilinear exposures of an iron-rich underlying unit of the flat sand sheet.

Safsaf region↗
USGS1986

Use of dust storm observations on satellite images to identify areas vulnerable to severe wind erosion

Blowing dust is symptomatic of severe wind erosion and deterioration of soils in areas undergoing dessication and/or devegetation. Dust plumes on satellite images can commonly be traced to sources in marginally arable semiarid areas where protective lag gravels or vegetation have been removed and soils are dry, as demonstrated for the Portales Valley, New Mexico. Images from Landsat and manned orbiters such as Skylab and the Space Shuttle are useful for illustrating the regional relations of airborne dust plumes to source areas. Geostationary satellites such as GOES are useful in tracking the time-histories of episodic dust storms. These events sometimes go unrecognized by weather observers and are the precursors of long-term land degradation trends. In areas where soil maps and meteorological data are inadequate, satellite images provide a means for identifying problem areas where measures are needed to control or mitigate wind erosion. ?? 1986 D. Reidel Publishing Company.

Climatic Change↗
USGS1982

Subsurface valleys and geoarcheology of the eastern Sahara revealed by shuttle radar

The shuttle imaging radar (SIR-A) carried on the space shuttle Columbia in November 1981 penetrated the extremely dry Selima Sand Sheet, dunes, and drift sand of the eastern Sahara, revealing previously unknown buried valleys, geologic structures, and possible Stone Age occupation sites. Radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand- and alluvium-filled valleys, some nearly as wide as the Nile Valley and perhaps as old as middle Tertiary. The now-vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat, hyperarid region. Underfit and incised dry wadis, many superimposed on the large valleys, represent erosion by intermittent running water, probably during Quaternary pluvials. Stone Age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation. The presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present-day oases which have been centers of episodic human habitation. Radar penetration of dry sand and soils varies with the wavelength of the incident signals (24 centimeters for the SIR-A system), incidence angle, and the electrical properties of the materials, which are largely determined by moisture content. The calculated depth of radar penetration of dry sand and granules, based on laboratory measurements of the electrical properties of samples from the Selima Sand Sheet, is at least 5 meters. Recent (September 1982) field studies in Egypt verified SIR-A signal penetration depths of at least 1 meter in the Selima Sand Sheet and in drift sand and 2 or more meters in sand dunes.

eastern Sahara↗
USGS1982

Shuttle imaging radar experiment

The shuttle imaging radar (SIR-A) acquired images of a variety of the earth's geologic areas covering about 10 million square kilometers. Structural and geomorphic features such as faults, folds, outcrops, and dunes are clearly visible in both tropical and arid regions. The combination of SIR-A and Seasat images provides additional information about the surface physical properties: topography and roughness. Ocean features were also observed, including large internal waves in the Andaman Sea.

Andaman Sea, Indian Ocean↗
USGS1981

Stratigraphy of the Caloris basin, Mercury

Caloris basin, Mercury’s youngest large impact basin, is filled by volcanic plains that are spectrally distinct from surrounding material. Post-plains impact craters of a variety of sizes populate the basin interior, and the spectra of the material they have excavated enable the thickness of the volcanic fill to be estimated and reveal the nature of the subsurface. The thickness of the interior volcanic plains is consistently at least 2.5 km, reaching 3.5 km in places, with thinner fill toward the edge of the basin. No systematic variations in fill thickness are observed with long-wavelength topography or azimuth. The lack of correlation between plains thickness and variations in elevation at large horizontal scales within the basin indicates that plains emplacement must have predated most, if not all, of the changes in long-wavelength topography that affected the basin. There are no embayed or unambiguously buried (ghost) craters with diameters greater than 10 km in the Caloris interior plains. The absence of such ghost craters indicates that one or more of the following scenarios must hold: the plains are sufficiently thick to have buried all evidence of craters that formed between the Caloris impact event and the emplacement of the plains; the plains were emplaced soon after basin formation; or the complex tectonic deformation of the basin interior has disguised wrinkle-ridge rings localized by buried craters. That low-reflectance material (LRM) was exposed by every impact that penetrated through the surface volcanic plains provides a means to explore near-surface stratigraphy. If all occurrences of LRM are derived from a single layer, the subsurface LRM deposit is at least 7.5–8.5 km thick and its top likely once made up the Caloris basin floor. The Caloris-forming impact would have generated a layer of impact melt 3–15 km thick; such a layer could account for the entire thickness of LRM. This material would have been derived from a combination of lower crust and upper mantle.

Icarus↗
USGS1979

Erosional scarps on Io

Irregular or fretted scarps on Io are similar to those found on Earth and Mars. A sapping mechanism involving liquid SO2 is proposed to explain these complexly eroded terrains on Io. ?? 1979 Nature Publishing Group.

Nature↗
USGS1979

The Jupiter system through the eyes of Voyager 1

The cameras aboard Voyager 1 have provided a closeup view of the Jupiter system, revealing heretofore unknown characteristics and phenomena associated with the planet's atmosphere and the surfaces of its five major satellites. On Jupiter itself, atmospheric motions—the interaction of cloud systems—display complex vorticity. On its dark side, lightning and auroras are observed. A ring was discovered surrounding Jupiter. The satellite surfaces display dramatic differences including extensive active volcanism on Io, complex tectonism on Ganymede and possibly Europa, and flattened remnants of enormous impact features on Callisto.

Science↗
USGS1978

Geologic map of the Coprates Quadrangle of Mars

The Coprates quadrangle lies to the east of the Tharsis volcanic complex and the Noctis Labyrinthus tectonic complex. To the north are the plains of Lunae Planum, to the east the vast patches of chaotic terrain and the large sinuous channels that trend northward to the Chryse Planitia. On the southwest is the Thaumasia Fossae region of the tectonically deformed cratered terrain, to the southeast, the Argyre Basin, the best preserve of the ancient Martian impact basins. The geology of the Coprates quadrangle is dominated by the Valles Marineris chasma system, which stretches in a east-southeast direction for about 2,500 km across the quadrangle. Its maximum width is about 600 km form the north rim of Ophir Chasma to the south rim of Melas Chasma. The terminus of Valles Marineris at the eastern edge of the map is about 500 km wide in the north-south direction. Individual segments of the chasma system are 100 to 150 km wide and 2 to 4 km deep. Much of the geology described here is common to other regions of Mars and has been discussed previously not only in summary papers but by other quadrangle mappers. Preliminary attempts at the regional geology of Mars have been made by McCauley and others (1972) and Carr and others (1973). Those units and features common to other parts of Mars are discussed first. The focus of this discussion is on Valles Marineris and those features that are unique to this quadrangle.

IMAP↗
USGS1977

Orientale and Caloris

Applications of experimental explosion-crater data to Orientale and recent geologic mapping of the basin have produced a new stratigraphy and genetic model for Orientale that are also applicable to Caloris. The inner-basin scarp of Orientale is thought to be a bench separating the upper parts of the basin from its deep bowl-shaped interior. The elongated and complexly fractured domes of the basin floor formed by inward compression in the terminal stages of the cratering sequence. The Inner Montes Rook are considered a central peak ring. The Montes Rook and the nonlineated knobby and associated smoother materials that overlie the Cordillera scarp around much of its circumference are the uppermost parts of the overturned rim flap which formed early in the cratering event. The knobs and smaller massifs are probably coherent blocks quarried from deep within the moon. They were among the last materials to leave the basin and had little radial momentum unlike the lineated Hevelius which formed earlier by disaggregation of the rim flap, secondary cratering, and the ground surge. The Cordillera scarp, best seen on the east side of the basin but poorly developed and discontinuous on the west, is a primary feature formed early in the crater excavation process by basinward motions of the walls and the fractured zone beyond the rim of the expanding cavity. The Cordillera scarp is overlain by ejecta over most of its extent, and post-basin internal slumping, previously thought to be important, must be a subordinate process in development of the scarp. The basin fill in Caloris has no counterpart in Orientale but the materials between the most prominent scarp and the weakly developed outer scarp appear to be the degraded and possibly mantled equivalents of the massifs and knobs associated with the Montes Rook. The radially lineated terrain that generally lies beyond the outer scarp of Caloris is considered the subdued counterpart of the Hevelius Formation, which generally shows the same relation to the Cordillera scarp at Orientale. Thus, the prominent innermost scarp of the Caloris basin is the equivalent of the Montes Rook. Beyond this scarp is the overturned flap covered by large blocks and massifs derived from a deep horizon in Mercury where the bedrock is more coherent than the upper impact-brecciated layers. The radially lineated deposits, as in Orientale, are earlier-arriving basin ejecta and secondary-crater materials mixed with the pre-basin surface all of which were modified by the ground surge. This comparison between Orientale and Caloris suggests that one or more buried ring structures should be present inside Caloris and that Mercury is also layered internally as is the moon. The differences in spacing and development of the ring structures or circumferential scarps of Orientale and Caloris are probably gravitational effects. ?? 1977.

Physics of the Earth and Planetary Interiors↗
USGS1977

Geologic map of the west side of the Moon

The west limb region of the M oon consists of highly cratered terra rising 5 km or more above the mare of Oceanus Procellarum and most of the lunar near side. Crustal material in this area of large basins and craters has been redistributed repeatedly by giant impacts. The early historical record of these events is apparently preserved in a complex of interlayered breccias, which may be partly exposed in the walls of the larger craters. Orientale, the last multiringed basin, was formed early in lunar history during the wanning stages of high impact flux by a large body probably impacting the surface obliquely from the northeast. Ejecta from this impact was widely scattered by over the Moon and appears to form some of the plains materials. Although the major landforms of the Oriental basin were developed instantaneously in geologic terms, isostatic adjustments were more protracted; the accompanying structural dislocations including concentric and radial faults in the floor material may have continued u p to the time of mare basalt flooding after basin formation. Subsequent impacts have produced craters generally less than 60 km diameter.

IMAP↗
USGS1973

Geologic map of the Grimaldi quadrangle of the Moon

The Grimaldi quadrangle lies at the southwest margin of Oceanus Procellarum about 1,000 km east of Orientale, the youngest o f the lunar multi-ringed basins. The distal ends of the ejecta blanket surrounding the Orient al e basin partly covers the western third of the quadrangle. The relatively small, two-ring Grimaldi basin is in the northwest corner of the quadrangle, and the Humorum basin l ies about 750 km to the southeast. A vestigial multi-ring basin mostly engulfed by mare appears to control the distribution of terra and mare along the southwest margin of Oceanus Procellarum ; the craters Hansteen and Billy are on a northwe s t-trending topographic high which represents part of the ring system of this basin. Terra materials of distinctive texture, apparently unrelated to multi-ring basins and probably of volcanic origin, occupy the central parts of the quadrangle.

IMAP↗