Sedimentary characteristics and lithofacies paleogeography of Sinian in Tarim Basin

Abstract

Sinian layer is about to become the hydrocarbon exploration potential target in Tarim Basin. Accurate understanding of Sinian distribution and lithofacies paleogeographic characteristics in Tarim Basin is not only a basis of further exploration, but also a key to restore the early tectonic-sedimentary evolution history of Tarim Basin. Based on comprehensive analysis of Sinian field outcrop data in the periphery of Tarim Basin, intra-basin drilling data and seismic data in combination with published research achievements, the Sinian distribution, tectonic setting, depositional system and lithofacies paleogeographic characteristics of Tarim Basin were explored in this study. Research shows that there are three types of Sinian depositional system in Tarim Basin, i. e., clastic depositional system, clastics-carbonate mixed depositional system and carbonate depositional system, vertically presenting the clastic sedimentary-carbonate sedimentary evolution characteristics. These three types of depositional system correspond to three times of Sinian transgressive-regressive cycle. The transgression in the initial period of the Early Sinian (ZSQI) led to the formation of clastic depositional system in the lower member of Lower Sinian. The transgression in the late period of the Early Sinian (ZSQII) resulted in the clastic-carbonate mixed depositional system in the upper member of Lower Sinian. The transgression in the initial period of the Late Sinian (ZSQIII) led to the Upper Sinian carbonate depositional system. Due to three transgression processes, three unconformities were formed at the middle and top of Lower Sinian as well as the top of Upper Sinian. With the breakup of the Neoproterozoic supercontinent Rodinia, Tarim Basin entered the continent rifting phase. The Sinian period was the intracratonic depression and passive continental margin evolution stage with the paleo-geographic characteristics of uplift in the south and depression in the north. In the Early Sinian, Bachu-Tazhong-Southeast Tarim Uplift and Tabei residual paleo-land were developed with the littoral-shelf environment in the north and littoral-shelf-bathyal environment in the southwest. In the Late Sinian, the Tabei paleo-land disappeared, where tidal flat environment existed in the north, and passive continental margin neritic environment in the southwest.