EVIDENCE OF NEOTECTONIC IMPACT ON A LARGE SEDIMENTARY BASIN BETWEEN TIBETAN PLATEAU AND GOBI ALTAY,NW CHINA

The Ejina( Gaxun Nur) Basin-enclosed by the Tibetan Plateau in the south and the Gobi Altay in the north hascontinuously evolved as a strong continental endorheic depositional environment. Medium scale geomorphological mappingby Landsat- and Corona-Images as well as SRTM-topographic data, combined with field-surveys and geophysicalinvestigation provides evidence for tectonic impact on sedimentary processes during the Late Quaternary.Analyses of SRTM-Data and Landsat-Images reveal a system of up to 20m high inverted channels developed on theinactive eastern part of the large Hei river drainage delta south of the ancient lake Juyanze. The complex evolution of theselandforms requires a relative lowering of the lake basin at least two times since the last 40ka. A 26m high cliff section ofgravel-covered lake sediments within the Juyanze paleolake indicates a strong subsidence of the lake bottom of 10m/1000yrssince 18kaB. P.North of Ejina river oasis a distinct north-south striking scarp up to 13m high constitutes the eastern margin of theGaxun Nur. Palaeodrainage channels derived from the Gobi Altay. They display a sinistral offset of some decametres alonga set of WE-trending faults. The rhombic shape of the modern dry Gaxun Nur, fossil cliffs,well preserved beach ridges alongthe margins of the palaeolake system as well as gravel covered topsets of lacustrine sediments indicate local displacements ofmorphological features. The displacements of lake sediments at the southern margin of the modern Gaxun Nur Basin imply asubsidence of at least 0.81m/1000 yrs since 25kaB. P. as a result of a pull-apart development due to the left stepping faultsin a sinistral system.

The Ejina（ Gaxun Nur） Basin-enclosed by the Tibetan Plateau in the south and the Gobi Ahay in the north has continuously evolved as a strong continental endorheic depositional environment. Medium scale geomorphological mapping by Landsat- and Corona-Images as well as SRTM-topographic data, combined with field-surveys and geophysical investigation provides evidence for tectonic impact on sedimentary processes during the Late Quaternary. Analyses of SRTM-Data and Landsat-Images reveal a system of up to 20m high inverted channels developed on the inactive eastern part of the large Hei river drainage delta south of the ancient lake Juyanze. The complex evolution of these landforms requires a relative lowering of the lake basin at least two times since the last 40ka. A 26m high cliff section of gravel-covered lake sediments within the Juyanze paleolake indicates a strong subsidence of the lake bottom of 10m/1000yrs since 18kaB. P. North of Ejina river oasis a distinct north-south striking scarp up to 13m high constitutes the eastern margin of the Gaxun Nur. Palaeodrainage channels derived from the Gobi Ahay. They display a sinistral offset of some decametres along a set of WE-trending faults. The rhombic shape of the modern dry Gaxun Nur, fossil cliffs,well preserved beach ridges along the margins of the palaeolake system as well as gravel covered topsets of lacustrine sediments indicate local displacements of morphological features. The displacements of lake sediments at the southern margin of the modern Gaxun Nur Basin imply a subsidence of at least 0. 81m/1000 yrs since 25kaB. P. as a result of a pull-apart development due to the left stepping faults in a sinistral system.