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

Abstract 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.

[1]  C. Haynes,et al.  Large-Scale, Low-Amplitude Bedforms (Chevrons) in the Selima Sand Sheet, Egypt , 1989, Science.

[2]  G. Schaber,et al.  Neolithic adaptation and the Holocene functioning of Tertiary palaeodrainages in southern Egypt and northern Sudan , 1989, Antiquity.

[3]  G. Schaber,et al.  The megageomorphology of the radar rivers of the eastern Sahara , 1986 .

[4]  B. Issawi,et al.  Review of Upper Cretaceous-Lower Tertiary Stratigraphy in Central and Southern Egypt , 1972 .

[5]  F. El-Baz,et al.  Desert landforms of southwest Egypt : a basis for comparison with Mars , 1982 .

[6]  F. Darbyshire,et al.  Metamorphic an magmatic events in the Uweinat — Bir Safsaf Uplift (Western Desert/Egypt) , 1984 .

[7]  G. Schaber,et al.  Subsurface Valleys and Geoarcheology of the Eastern Sahara Revealed by Shuttle Radar , 1982, Science.

[8]  R. Folk Longitudinal dunes of the northwestern edge of the Simpson Desert , 1971 .

[9]  D. A. Cook,et al.  Intraband radiometric performance of the Landsat Thematic Mappers. , 1984 .

[10]  R. Bagnold,et al.  Journeys in the Libyan Desert: 1929 and 1930. Part One , 1931 .

[11]  K. Glennie,et al.  Desert sedimentary environments , 1971 .

[12]  Ronald G. Blom,et al.  Radar Image Processing for Rock-Type Discrimination , 1982, IEEE Transactions on Geoscience and Remote Sensing.

[13]  G. Schaber,et al.  Uranium-Series Dated Authigenic Carbonates and Acheulian Sites in Southern Egypt , 1989, Science.

[14]  P. Chavez,et al.  DISCRIMINATION OF ALTERED BASALTIC ROCKS IN THE SOUTHWESTERN UNITED STATES BY ANALYSIS OF LANDSAT THEMATIC MAPPER DATA. , 1987 .

[15]  John F. McCauley,et al.  Acheulian Sites along the “Radar Rivers,” Southern Egyptian Sahara , 1988 .

[16]  R. E. Walker,et al.  Color enhancement of highly correlated images. I - Decorrelation and HSI contrast stretches. [hue saturation intensity , 1986 .

[17]  P. Chavez An improved dark-object subtraction technique for atmospheric scattering correction of multispectral data , 1988 .

[18]  P. Chavez Radiometric calibration of Landsat Thematic Mapper multispectral images , 1989 .

[19]  C. Breed,et al.  Paleodrainages of the Eastern Sahara-The Radar Rivers Revisited (SIR-A/B Implications for a Mid-Tertiary Trans-Afnrcan Drainage System) , 1986, IEEE Transactions on Geoscience and Remote Sensing.

[20]  J. McCauley,et al.  Relict drainages, conical hills, and the eolian veneer in southwest Egypt—Applications to Mars , 1982 .

[21]  John F. McCauley,et al.  Paleorivers and geoarchaeology in the southern Egyptian Sahara , 1988 .

[22]  C. Haynes,et al.  Great Sand Sea and Selima Sand Sheet, Eastern Sahara: Geochronology of Desertification , 1982, Science.

[23]  G. Schaber,et al.  Shuttle Imaging Radar: Physical Controls on Signal Penetration and Subsurface Scattenng in the Eastern Sahara , 1986, IEEE Transactions on Geoscience and Remote Sensing.

[24]  G. Hunt Visible and near-infrared spectra of minerals and rocks : I silicate minerals , 1970 .

[25]  P. Munson,et al.  Prehistory of the eastern Sahara , 1980 .

[26]  John W. Salisbury,et al.  Visible and near infrared spectra of minerals and rocks. II. Carbonates , 1971 .

[27]  J. McCauley,et al.  Sand sheets of the eastern Sahara and ripple blankets on Mars , 1987, Geological Society, London, Special Publications.

[28]  J. C. Harms,et al.  Major Subdivisions and Depositional Environments of Nubia Strata, Southwestern Egypt , 1979 .

[29]  J. L. Barker,et al.  Landsat MSS and TM post-calibration dynamic ranges , 1986 .