212 / 2019-06-20 10:51:55

The sedimentary facies characteristics and lithofacies paleogeography of Yingshan formation during Middle-Lower Ordovician in Tarim Basin，western China

carbonate; sedimentary facies; lithofacies paleogeography; Yingshan Formation; Tarim Basin

The carbonate rocks of the Yingshan Formation are the main target for exploration in the Ordovician deposits of the Tarim Basin, and paleogeographic study of this period can establish a firm foundation for the next phase of exploration. Combined with geological and seismic data, the stratigraphic, petrological and sedimentary characteristics of the Yingshan formation have been systematically studied. Further, the ‘single-factor analysis and multi-factor comprehensive mapping’ method has been adopted to ensure clarity in lithofacies paleogeography. In this paper the method centers around 4 key factors: strata thickness; deep water sedimentary rock content; limestone content, and grainstone content. Results show that the Yingshan formation is widely distributed in Tarim Basin. Carbonate rocks dominate and are distributed in the western part. Clastic rocks are distributed in the eastern part. Open platform, platform margin, slope and basin four facies and relevant subfacies and microfacies are identified. The main subfacies are granular bank, followed by bank interact sea. Generally, the paleogeographic characteristics can be summarized as ‘western platform and eastern basin’. The deposits in the western platform consist of carbonate rocks; the deposits in the eastern basin are clastic rocks. From west to east, the sedimentary facies of the Yingshan formation vary from platform to slope and basin. From north to south, there is no obvious sedimentary facies transition, and facies are characterized entirely by platform deposits.