Paleogeographic and sedimentary evolution of Meso–Neoproterozoic strata in the Ordos Basin, western North China Craton

Abstract

Exploration for deep and ultra–deep hydrocarbon resources plays a significant role in meeting the world's increasing energy demand. Meso–Neoproterozoic strata are considered as a possible target interval for hydrocarbon exploration in deep formations. In this regard, bitumen and potential source rocks have been identified in the Meso–Neoproterozoic strata of the Ordos Basin, western North China Craton, yet the distribution and paleogeographic evolution of these strata remain unclear. In this study, recent drilling data were combined with seismic data and fieldwork to examine the paleo environment of these Meso–Neoproterozoic strata. The results indicate that the Meso–Neoproterozoic strata are mostly distributed in the southwestern part of the basin and grow thinner from the southwest to the northeast. These sediments developed in an intracontinental rift setting with four NE–trending rift troughs having formed during the Changcheng Period. Sedimentary facies during this period were mainly fluvial–deltaic, littoral–neritic marine (quartzitic), and transitional facies. In the Jixian Period, the basin was mainly a marginal depression with a narrow sedimentation range in which carbonate tidal flats and dolomites with stromatolites and siliceous interlayers developed. During the Sinian Period, the basin was a marginal depression characterized by deposition of glacial moraine conglomerate along the southwestern margin. The Changcheng System neritic facies developed in the rift margin and northern margin of the basin controlling the distribution of total organic carbon of argillaceous source rock. The determination of the distribution, characteristics, and paleogeographic evolution of Meso–Neoproterozoic sediments is conductive to the prediction of source rock distribution, and is important for hydrocarbon exploration in the Ordos Basin.