Microfacies, geometry and growth phases of microbial mound in Gucheng area, Southeastern Tarim Basin, China

A microbial mound is favorable carbonate reservoir for petroleum exploration, particularly in the deep tight reservoirs the Tarim petroliferous basin. Due to lack of effective research methods, it is difficult to analyze its unique sedimentary structure evolution process. In this study, , the investigation of petrographic texture, microfacies, geometry, and growth phases of microbial mound in Gucheng area, Southeastern Tarim Basin was conducted using cores, thin -sections, logging, 3D seismic data, and geochemical test data. The findings can be utilized to reconstruct dynamic evolution of the microbial mounds and discuss the controlling factors. The major results are as follows: (1) Gucheng area is located in the margin facies belt of a relatively high-energy platform, conducive the growth and development of microbial mounds. Seven petrographic textures were identified, forming four sedimentary microfacies types: mound base, mound core, mound flat, and mound wing. (2) During the Middle and Upper Cambrian periods, four phases microbial mound sedimentation occurred successively, with each phase superimposed in the oceanward direction. The development covered more than 1400 km2, with stripped distribution that extends from south to north in the plane. (3) The four phases of microbial mound complexes reflect the gradual evolution process of carbonate platform, transitioning from low angle slope to a platform margin in regional sea level regression environment. The microfacies geometry and growth phases of microbial mounds were mainly controlled by sea level change and palaeogeomorphology.