Abstract:

Lower Cambrian tempestites are found in Xiaoerbulak Formation in Sugaitblak area, Tarim Basin. The major storm sedimentary markers are scouring filling structures, storm flowgenerated gravelstones and hummocky cross stratifications (HCS). Based on outcrop observation in the field and thin section, a total of five types of storm deposits are recognized according to the synthesis of storm sediments, sedimentary position and depositional markers. Type Ⅰ is represented by the graded lamination in millimeter or centimeter scale downcutting the underlying microbial reef. They are formed by distal storm turbidity currents below stormwave base. Type Ⅱ is composed of allodapic storm gravelstone (of member A), graded member (B), parallel lamination member (C) and black calcareous shale with horizontal bedding (E2), which are deposited at the lower part of gentle slope between the storm and the fine weather wave bases. Type Ⅲ consists of storm bioclast, gravelstone, parallel lamination and HCS, depositing at the upper part of the slope. Type Ⅳ is characterized by gutter casts and composite HCS, which are formed in the vicinity of the fair weather wave base. Type Ⅴ develops storm intraclastic limestones and scouring filling structures (A) and parallel lamination (C), overlying cyanobacteria reefbank collapsing deposition in fair weather. They are formed in the front of platform margin above fair weather wavebase. The depositional evolution of tempestites is: the deep water shelf→the lower part of gentle slope→the upper part of gentle slope→the front of platform margin, which are characteristic of shallowing upward. The discovery and researches of tempesites in the studied area are of great significances for understanding the palaeolatitude and palaeoplate evolution as well as the palaeogeographic environments and sedimentary evolution in the Early Cambrian of Tarim plate.

Key words:  Sugaitblak area, Xiaoerblak Formation, tempestites, depositional model, geological significance