Late Ediacaran to Early Cambrian tectonic–sedimentary controls on Lower Cambrian black shales in the Tarim Basin, Northwest China

Abstract

Lower Cambrian black shales contain unique metazoan fossils that record the origins and diversification of early animals, and are also important hydrocarbon source rocks with a global distribution. The spatial distribution and hydrocarbon potential of Lower Cambrian black shales in the Tarim Basin, northwest China, are still poorly constrained due to deep burial and the few previous studies of these rocks. In this study, we integrated outcrop, seismic, and drilling data in order to examine the tectonic–sedimentary evolution of the Tarim Basin from the late Ediacaran to Early Cambrian, and its effects on the distribution of Lower Cambrian source rocks. During rifting related to breakup of the Rodinia supercontinent, the Tarim Basin was filled with clastic rocks of Cryogenian to early Ediacaran age. Post-rift carbonates interbedded with siliceous and argillaceous sediments were then deposited during a widespread transgression in the late Ediacaran–Early Cambrian. The Tarim Basin can be subdivided into northern and southern parts by a central paleo-uplift region that had a high paleo-topography. Although tectonism at the end-Ediacaran is variably recorded in some outcrops and by seismic data, the Tarim Basin did not experience a change in its tectonic and sedimentary framework at this time, indicating it inherited the structure of the Early Cambrian and late Ediacaran basins. Therefore, the spatial distribution of the Lower Cambrian source rocks was controlled by the paleo-topography of the late Ediacaran basin, and these source rocks can be divided into three members. Black siliceous shales are one of the most productive source rocks in the Tarim Basin, are widely distributed in the northern Tarim Basin, and have excellent petroleum potential.