Sinian tectonic evolution and distribution of source rocks in northwest Tarim Basin, China

Abstract

Tarim Basin experienced several tectonic events during Precambrian, including the Neoproterozoic Rodinia supercontinent assembly/breakup event and Snowball Earth, and has great potential for oil generation in the ultra-deep deposits. The Precambrian strata in the northwest margin of the Tarim Basin (abbreviated as the northwest Tarim) are well exposed, which play a key role for understanding the tectonic evolution of Neoproterozoic. The northwest Tarim underwent the transformation that tectonic setting changed from convergence to expansion in the Neoproterozoic, and finally formed a continental rift until 572 Ma. During this period, thick layer of black mudstone was deposited, which probably was the important petroleum source rock. The TOC of Sinian mudstones is between 0.32 and 1.25%, with an average value of 0.53%. The average of rock pyrolysis parameters (S1+S2) is 0.17 mg/g, Ro is between 1.61% and 2.52%, and the average of chloroform asphalt "A" is 0.0076%. These geochemical characteristics indicate that the source rocks are now highly mature. The carbon isotopes of kerogen are between −27.2‰ and −30.2‰ and biomarkers show that algae and bacteria are the main source input, therefore, the Sinian source rock mainly contains marine type I kerogen from a single source. The above data show that the Sinian source rock is a set of effective source rocks. The tectonic evolution of northwest Tarim was reconstructed based on the age characteristics of detrital zircons, and it indicated that the Sinian source rocks were controlled by continental rift deepening and large-scale transgression. Combined with seismic reflection characteristics, the distribution of Sinian source rocks are shown, which provides an important basis for Precambrian oil and gas exploration.