The "Uweinat Desert" of Egypt, Libya and Sudan: a Fertile Field for Planetary Comparisons of Crater Forms
Total Page：16
File Type：pdf, Size：1020Kb
THE "UWEINAT DESERT" OF EGYPT, LIBYA AND SUDAN: A FERTILE FIELD FOR PLANETARY COMPARISONS OF CRATER FORMS. Farouk El-Baz, National Air and Space Museum, Smithsonian Institution, Washington, D.C. 20560. The Western Desert of Egypt and adjacent parts of Libya and Sudan constitute the driest expanses of land on Earth (1). The southeastern part of the Western Desert has been named the Arba'in Desert (2). The southwestern part of the Western Desert and adjacent areas of Libya and Sudan are here named the Uweinat Desert after the prominent, 60 x 40 km-large, 1900 m-high mountain at the intersection of the borders of the three countries (Fig. 1, left) . This region of the eastern Sahara displays numerous features that have been correlated with surface features of Mars (3,4,5). Of particular signifi- cance are the wind streaks caused by lag deposits and sand dunes (4,5), the pitted and fluted rocks strewn on the surface (5,7), and the dry valleys of fluvial origin that resemble tributaries of martian canyons (4,5). In addition there are both impact and volcanic crater forms (8) that can be correlated with craters on the surfaces of terrestrial planetary bodies. This paper deals with these crater forms, including the first report on an impact crater in the Great Sand Sea. Landsat images revealed a group of peculiarly circular features about 130 km E-SE of Gebel Uweinat (A in Fig. 1, left). The rims of these structures are marked by discontinuous arcs and knobs in a terrain that is heavily modified by eolian action. Inside the circular structures, the terrain is relatively smooth and flat; outside it is hummocky and lineated (8). These characteristics make the craters somewhat analogous to the old circular depressions in the heavily cratered terrain of the lunar highlands, the southern hemisphere of Mars, and the plains of Mercury. The craters have been named after the explorers whose tracks came nearest to them (Fig. I., right). Approximately 100 km north of this site, there is another cluster of craters displaying different forms (B in Fig. 1, left). Some of these were discovered by Clayton in 1931 and others by Peel in 1938 (9) and the whole field is named the Clayton craters (Fig. 2a). Individual craters cover areas of only tens of square meters up to 100 km2. Most are circular, but some are elongate in a NE direction. Some of the craters were investigated in the field and found to be volcanic in origin, mostly volcanic cones and maars (Fig. 2b). Other craters in the Uweinat Desert are multi-ringed structures of impact origin S and SW of the Libyan glass region (C in Fig. 1, left). The first is Z5'E 26'E I EGYPT I I Figure 1. Location map of discussed features in the Uweinat Desert (left), and sketch map of a crater cluster in area A in the Sudan (right). O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System UWEINAT DESERT EL-BAZ, FAROUK Figure 2. Landsat image (E-1131-08141) of Clayton Craters northeast of Gebel Uweinat (A) , and ground view of a maar (B) . 11.5 km across with a 17 km diameter outer ring (10). It was named the Oasis structure, because it was called to the attention of J. R. Underwood by geologists from the Oasis Oil Company of Libya, and was later renamed the Oasis astrobleme (10). The impact origin of this structure was established by studies of shock metamorphic effects in the host sandstone, particularly planar structures in quartz (11). Some 80 km north of the Oasis astrobleme is another multi-ringed crater approximately 2.8 km in diameter. It is known as the BP structure because it was first discovered by British Petroleum geologists (12). It shows a distinct central peak and two rings. In addition to this there is a 3.5 km elongate structure of unknown origin, which is 160 km NE of Kufra (11). Landsat images of the Great Sand Sea reveal another crater of probable impact origin. It is located amidst linear dunes of 70 km average length, and its presence appears to have affected the orientation of smaller 10-20 km dunes. The rim crest of the crater is 3.8 km in diameter on the average with two lips that increase the diameter to over 4 km. The crater which lies 320 km east of Kufra has a polygonal outline reminiscent of that of Meteor Crater in Arizona and numerous craters on the Moon and terrestrial planets. Because of a dark splotch on its south side, the crater is particularly analogous to those in the Cerberus region of Mars. Since there are no named features in its vicinity and no explorers came near its site, it is here named "El-Baz Crater." Its features will be studied in detail during a planned field investigation. References 1. Henning, D. and Flohn, H. (1977) Climate aridity index map. UNEP. 2. Haynes, C.V. (1980) Advances in Planet. Geol., NASA TM, in press. 3. El-Baz, F. (1977) Smithsonian Studies in Air and Space, v. 1, Wash., D.C. 4. El-Baz, F. and Maxwell, T.A. (1979) Lunar Planet. Sci. X, p. 349-351. 5. El-Baz, F. et al. (1980) Geogr. Jour., v. 146, p. 51-93. 6. El-Baz, F. et al. (1979) JGR, v. 84, B 14, p. 8205-8221. 7. McCauley, J.F. et al. (1979) JGR, v. 84, B 14, p. 8222-8232. 8. El-Baz, F. and Issawi, B. (1981) NASA Tech. Mem. (in press). 9. Peel, R.F. (1939) Geogr. Jour., v. 113, n. 4, p. 295-307. 10. Dietz, R.S. and McHone, J.F. (1979) NASA SP-412, v. 11, p. 183-191. 11. French, B.E. et al. (1974) Geol. Soc. Amer. Bull. 85, p. 1425-1428. 12. Martin, A.J. (1969) Nature, v. 223, p. 940-941. O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System UWEINAT DESERT EL-BAZ, FAROUK Figure 3. Landsat photographs of impact structures named Oasis astrobleme (I), PB structure (2), and El-Baz Crater (3). O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System .