Characteristics of tectonic-lithofacies paleogeography in the Lower Cambrian Xiaoerbulake Formation, Tarim Basin

The study aims to discover new prospective areas for deep oil and gas exploration based on the understanding of tectonic and sedimentary response characteristics and evolution patterns of the Xiaoerbulake Formationin, Tarim Basin. Under the guidance of marine carbonate rock sequence stratigraphy and reservoir sedimentology, it's made certain that the Lower Cambrian Xiaoerbulake Formation mainly develops restricted-semi-evaporitic platform, open platform, platform margin, slope-basin facies according to core, logging and seismic data and thin section observation, combined with the features of tectonic paleo-geomorphology. These sedimentary facies can in turn be subdivided into multiple subfacies and microfacies, and their distribution is characteristic of zonation and inheritance. The fine interpretation of the two-dimensional seismic lines across the basin helps to identify the features of seismic responses of the main Cambrian sedimentary facies in Tarim Basin, and recognize six types of seismic facies, namely the intra-platform microbial mound/shoal(SF1), intra-platform low(SF2), inter-mound/bank sea(SF3), gypsum-salt lake(SF4), platform margin(SF5)and slope-basin(SF6). Then the boundary of sedimentary facies for each facies zone was delineated and the relation of facies zones distribution with paleostructure and paleogeomorphology was revealed. According to the isopach map of the Xiaoerbulake Formation, it's made clear that there is an EW-trending paleo-uplift in the southern basin, and two depressions in the eastern and central basin. The First Terrace lies in the southwestern basin, which transits from the wide and gentle Level 1 slope-break towards the central depression, while the narrow and steep Level 2 slope-break in the central basin rapidly transfers to a deep depression towards the east. In addition, the seismic interpretation results, analysis of outcrop, observation of cores as well as microscopic observation of thin sections were used to generate the lithofacies paleogeographic map of the Lower Cambrian Xiaoerbulake Formation, providing favorable evidences for the exploration of deep carbonate oil and gas in the Lower Cambrian Xiaoerbulake Formation of Tarim Basin. © 2019, OIL & GAS GEOLOGY Editorial Board. All right reserved.