High resolution Sequence Stratigraphy of Baikouquan Formation in Mahu Sag, the Junggar Basin

Abstract

Baikouquan Formation of Lower Triassic in Mahu Sag of the Junggar Basin is one of the main reservoirs in the basin, and typical large lacustrine fan delta deposits are developed. This study is based on core observations of the western slope of the Mahu Depression. Through logging, logging, seismic and other data, and applying the principle of high-resolution sequence stratigraphy baseline cycles, a systematic analysis was conducted on the cyclic interfaces of the Baikouquan Formation at all levels on the western slope of the Mahu Depression. The research results indicate that: 1. The bottom of the Baikouquan Formation is in angular unconformity contact with the underlying Urhe Formation. The Baikouquan Formation is generally an upward deepening asymmetric cycle with a long-term base level rise, including the early stage of slow base level rise, the middle stage of continuous base level rise, and the late stage of rising to near symmetric cycle. These three stages have successively developed the sedimentary facies of the front edge of the shallow water fan delta with a retrogressive style The sedimentary facies of the outer front of the fan delta and the sedimentary facies of the front fan delta. The Baikouquan Formation as a whole is a set of retrogradational stratigraphic styles, with the bottom being the water retreat pole and the baseline being in an overall upward process. In terms of sedimentary facies, it gradually transitions from the front edge of the fan delta to the front fan delta, and vertically (from bottom to top), it goes from underwater distributary channels to front edge sheet sand and then to front fan delta mud (T1b3). The above conclusion provides a geological basis for the exploration and development of rich hydrocarbon depressions in Mahu Depression and other similar complex superimposed basins.