Microbialites from the Upper Cambrian in the Tarim Basin, Northwest China: implication for depositional environments

Microbialites from Penglaiba section, a well-exposed stratigraphic section in the northwestern area of the Tarim Basin are widely distributed throughout the Lower Qiulitage Formation of the Upper Cambrian. Stromatolites and thrombolites are recognized as the two major components. Thrombolites have two kinds of fabrics under the microscopy based on varying arrangements macroscopically, which are microbial reefs and clotted laminations. The microbial reefs are kind of round and irregular buildups with branched shapes and interconnection as frame, which played the major roles in protecting the other microbial structures against the tides and waves. Based on petrology, stratigraphy and micro-facies combination, depositional environments are indicated for varying water depths and energy. In addition, a model of peleaoenvironments is established in the Lower Qiulitage Formation. Both of thrombolites and stromatolites are associated in the subtidal zone, but in this sedimentary model, thrombolites deposited in the deeper water, in which this facies association is similar to what has happened in Bahamas.