A MARS ANALOG. A. S . Walker, MS 730, U

DRAINAGE IN GOBI TERRAIN : A MARS ANALOG. A. S. Walker, MS 730, U. S. Geological Survey, Reston, Ira. 22092. The Turpan Depression is a 50 ,000-h2 fault-fond interior drainage basin in Xinjiang Autonomous Region, People's Republic of China (fig. 1). The depression is named after Turpan County (43O N. , 89' E. ) , a small city in the north-central part of the basin and is bounded on the north, east, and west by the Bogda Mountains (6,500 m above sea level m3ximum elevation), and on the south by the Kuruktag buntains (1,500m). Both muntain ranges are part of the Tian Shan (Sky Mountains), a permanently glaciated range which was uplifted during the Cenozoic (Himlayan Uplift ) . The mountains are composed mainly of quartzite and other rr-etasedirnents; however, the southern slopes and foothills of the Bogda Mountains are conposed of red, and to a lesser extent white, sandstone, conglomerate, and mudstone, and are called the Flaming Mountains (850 rn in elevation). The lowest point in the basin is Aydingkol Lake (-154 m). The basin is extremely arid, windy and hot with a mxirm recorded sand temperature of 82.30 C. and a maximum recorded wind velocity greater than 110 dsec. (1). Tne Turpan Depression may be divided into two sermlconcentric belts. The area adjacent to the mountains, on gently sloping (1-3') alluv5al fans is primarily composed of black gobi (regionally unsorted loose subangular to subrounded quartzite gravels, predominately of pebble size, but with occasional cobbles) occupying an area 25-hn wide in the north and 15-kn wide in the south (fig. 2). Alluvim, artesian-spring-fed oases and lakes occupy the center of the basin. The gobi occupies a large deflation area in the basin fomd by the complex interaction of wind and water. Tnere are two areas of deposition, Sand Mountain, a 2,500 lan2 dune field southeast of Turpan (fig. 1), and a second area south of Turpan not visible on the image. Secause of the smll mount (10-30 rrun) of annual rainfall in the basin (2), the intermittent rivers are fed almost exclusively by the Tian Shan glaci~rs rather than by preci~itation. The streams initially flow over bedrock. When they reach the gobi they maintain their integrity for up to 15 km not with- standing a significant decrease in slope and the change in underlying mterial. At a distance down onto the fan, the streams begin to anastomose. The control- ling process changes ,from erosional to depositional and the water q~~ickly infiltrates the gobi and joins the pound-water supply. The stream patterns are a product of two enviromnts resulting in a mountain drainage system with well-deflned channels and an alluvium drainage system with hi@ infiltration and an anastomosing pattern. The velocity and volume of flow coming from the mountain drainage systen initially controls the behavior of the stream when it reaches the gobi, and thus the stream channels are not in equilibrium with the gobi terrain in which one would expect imdiate anastomsing. Figure 3 shows a 0.6-km wide channel as it leaves the Tian Shan and debouches in the gobi in an anastomosing pattern. This pattern can be readily identified by the color difference between the fine-grained li@t sand and the larger-mained dark metasediments. Other smaller anastomosing channels are also apparent on the image. Analysis of temporal Landsat data ir~dicatesthat the channels remain consistent for up to 4 years. O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System GOBI DRAINAGE Walker, A. S. Inasmuch as myinvestigators argue that channels on Mws were formed by running water, but not necessarily f'rom rainwater (for example, 3), and appear to debouche f'rom cratered hi@lands onto plains, and inasmuch as the gobi terrain resembles that of the Viking landing sites, the drainage pattern in the Turpan Depression gobi presents an excellent analog for the debouch- rent of fluids from martian channels. Figure 4, channel patterns at the muth of the %ja Vallis, Mars, shows channel morphology similar to that of the channels in fig. 3. Tne water that formed some of the channels on Mars may have originated in a area in which the channels were in a state of quasi-equilibrium with the martian surface environment. Tnis state my not have continued throua the entire length of the channels, however, and so% features near the mouths of the channels my reflect relic equilibrium states upstream, just as some reaches of the channels in the gobi are controlled by glacial runoff from the Tian Shan. Ac!mowledgement s Field work was conducted as a research grantee of the National Frogram- for .iicivanced Study and Research in China, administered by the National Academy of Sciences Coirnnittee on Scholarly Communication with the Peonlets Republic of China. Digital enhancement of Landsat data was completed at the Earth Resources Observation Systems (EROS) Data Center. I thank Xie Xiande, A. "rffford, D. :Elton and D. K~~insleyfor helnful discussions. References 1. >;ia Xunzheng and iiu Yong;lcan, 1978, Academia Sinica, Xinjlaqg, People's Republic of China. 2. Znu Zhenda, ~JLI Zhen, Liu Shu , arid Di Shengping, 1980, Acadexia Sinica, Gansu, People's Zepublic of C"nina. 3. Pieri, David, 1980, Trans. A.S.U., v. 61, p. 1020 O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System GO39 DRAiNAGE Walker, A. S. Figure 1.--Turpan Depression. Band Figure 2.--Gobi surface in the Turpan 7 of Landsat image 1073-04181. Depression. Area is 185 lanby 185 h. Xgure 3. --Anastomsing streams fed F'igure 4 .--Anastomsing channel by Tian Shan glaciers. Linear patterns at the muth of Maja contrast stretched ort ti on of Vallis. Viking image 20A56, 60 imge 1073-04151, 30 lan in lon- lan-in longitudinal direction. gitudinal direction. O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System .

Load more