Sedimentology of the distal fan and lake deposits of the Tianshui- Qinan Basin (Central China): evidences against a possible eolian origin

Abstract

In this paper we analyze two sections within the Tianshui-Qinan Basin, a closed basin in Central China. The deposits are Miocene and Pliocene in age and in recent times they have been considered as loess. The preliminary sedimentological study indicates a closed lacustrine basin, with a very flat topography in the inner parts. Periodical desiccation and subaerial exposure periods of both mudflats and shallow lakes caused important reworking of the sediments. The lake margins were ramp-like with different energy levels. Low energy lake margins are represented by marls, intraclastic and palus- trine limestones, whereas higher energetic levels are indicated by rippled sands and silts.