Provenance and paleogeography of Carboniferous–Permian strata in the Bayanhot Basin: Constraints from sedimentary records and detrital zircon geochronology

摘要

The Bayanhot Basin is a superimposed basin that experienced multiple-staged tectonic movements; it is in the eastern Alxa Block, adjacent to the North China Craton (NCC) and the North Qilian Orogenic Belt (NQOB). There are well-developed Paleozoic–Cenozoic strata in this basin, and these provide a crucial window to a greater understanding of the amalgamation process and source-to-sink relationships between the Alxa Block and surrounding tectonic units. However, due to intensive post-depositional modification, and lack of subsurface data, several fundamental issues—including the distribution and evolution of the depositional systems, provenance supplies and source-to-sink relationships during the Carboniferous– Permian remain unclear and thus hinder hydrocarbon exploration and limit the geological understanding of this basin. Employing integrated outcrop surveys, new drilling data, and detrital zircon dating, this study examines the paleogeographic distribution and evolution, and provenance characteristics of the Carboniferous–Permian strata in the Bayanhot Basin. Our results show that the Bayanhot Basin experienced a long-term depositional evolution process from transgression to retrogression during the Carboniferous–late Permian. The transgression extent could reach the central basin in the early Carboniferous. The maximum regional transgression occurred in the early Permian and might connect the Qilian and North China seas with each other. Subsequently, a gradual regression followed until the end of the Permian. The northwestern NCC appeared as a paleo-uplift area and served as a sediments provenance area for the Alxa Block at that time. The NCC, Bayanwula Mountain, and NQOB jointly served as major provenances during the Carboniferous–Permian. There was no ocean separation, nor was there an orogenic belt between the Alxa Block and the NCC that provided sediments for both sides during the Carboniferous–Permian. The accretion of the Alxa and North China blocks should have been completed before the Carboniferous period.