Geochronology, Geochemical Characteristics, and Main Controlling Factors of Reservoirs in Dolomite and Siliceous Rocks of the Upper Cambrian Lower Qiulitage Formation, Tarim Basin

 Laser ablation U-Pb dating technology for carbonate rocks has matured and plays a significant role in studies of carbonate reservoirs, tectonic activities, and related research. However, the lack of effective dating methods for siliceous rocks, which are extremely abundant in the Earth's crust, has constrained research into the diagenetic processes associated with them. Consequently, building upon the foundation of carbonate laser U-Pb dating, a laser U-Pb dating technique for siliceous rocks was successfully developed through a series of methodological improvements. Both carbonate and siliceous rock laser U-Pb dating were applied to the recently explored but less-studied reservoirs of the Upper Cambrian Lower Qiulitage Formation in the Tabei area of the Tarim Basin. Integrated with analyses including petrology, sedimentology, cathodoluminescence, trace and rare earth elements, in-situ carbon and oxygen isotopes, and elemental mapping, the following conclusions were reached: ① The dolomites of the Lower Qiulitage Formation in the Tabei area underwent multiple diagenetic stages. The first stage was a widely developed penecontemporaneous to shallow burial dolomitization. The second stage was a burial dolomitization, locally distributed along faults and induced by tectonic compression during the Early-Middle Devonian. The third stage was a hydrothermal dolomitization, also localized along faults, caused by Permian volcanic activity. Both the second and third stages accompanied by recrystallization, silicification, and mineral precipitation. ② The dolomite reservoirs of the Lower Qiulitage Formation are primarily developed within grain shoal sedimentary facies. Reservoir space primarily originated from meteoric water dissolution. Multiple episodes of burial fluids increased reservoir heterogeneity and partially destroyed pore spaces. Therefore, sedimentary facies of paleo-highland grain shoals, located away from fault activity zones of the Devonian and Permian periods, are favorable areas for reservoir development. The research outcomes provide effective theoretical support for the exploration of dolomite reservoirs in the Lower Qiulitage Formation. Furthermore, the successful application of laser dating techniques to both carbonate and siliceous rocks in this dolomite reservoir study offers new perspectives and methodologies for related research.

Keywords: Laser U-Pb dating of siliceous rocks; Laser U-Pb dating of carbonate rocks; Diagenesis; Reservoir genesis; Tabei area