Ostracod ecology of alluvial loess deposits in an eastern Tian Shan palaeo-lake (NW China)

Abstract

An alluvial loess sequence of 105 m thickness was studied in a steep mountainous desert valley in the eastern Tian Shan. Although no very clear remnants of a natural dam have yet been found, we conclude that probably a huge landslide downstream of the sequence resulted in a dam rising at least 105 m above the valley floor. Seven ostracod species including Ilyocypris bradyi, Eucypris lilljeborgi, Darwinula stevensoni and Limnocythere inopinata were found in the sediments and facilitated the reconstruction of the lake history. After the valley was filled suddenly, swamp conditions prevailed, leading to a fluctuating shallow lake and swamp environment at first and the formation of a deeper and more stable lake afterwards. Shallow water and swamp conditions again prevailed, succeeded by a more stable and deeper lake, until conditions changed once more to a shallow lake with a dense subaquatic vegetation. A last deeper lake period was followed by a second period of a shallow, densely vegetated lake. Freshwater conditions prevailed more or less during the entire lake evolution.