Late Carboniferous to Permian paleoclimatic and tectono-sedimentary evolution of the central Ordos Basin, western North China Craton
Authors: Tao Hua , Cui Junping 
Published: March 2024

The paleogeographic and tectonic environments of the North China Craton experienced dramatic transitions throughout the end-Carboniferous to Permian, having been depicted to record protracted subduction-collision orogenesis along the southern margin of the Paleo-Asian Ocean (present coordinates). The resultant topographic growth within the Andean-Type continental arc, which was constructed by the ocean plate subduction, has also significantly driven regional climatic shift from humid to arid, expressed by accumulation of coal-bearing tidal flat and deltaic facies of the Benxi, Taiyuan, Xiashihezi, and Shangshihezi formations to red-color seasonal lake associations of the Shiqianfeng Formation. To depict relations between topographic variation of the continental arc and depositional environment changes of the sink, we conducted a complied work incorporating petrology, geochemistry, and detrital zircon U-Pb geochronology on Carboniferous and Permian strata in the central Ordos Basin, western North China Craton. The geochemical data of 36 mudstone samples show that the depositional basin was characterized by oxygen-poor and anaerobic environment, as indicated by Ce/La>1.5 and Vi/(V+Ni) >0.54. The paleosalinity from deposition of the Benxi to Shiqianfeng Formation gradually decreased, reflecting the environmental transition from marine to continental environments. The geochemical signatures further reveal that the detrital materials are mainly derived from erosion of medium-acid volcanic rocks within a continental arc. In combination with sandstone petrologic data, we suggest that gneiss and intrusive rocks that made up of continental magmatic arc are the main provenance sources, in addition to a small portion of basic volcanic rocks. The U-Pb dating results of 563 detrital zircons from 6 Carboniferous&#8211;Permian clastic rocks yield three distinct age ranges: 260&#8211;470 Ma (29%), 1700&#8211;2100 Ma (40%), and 2200&#8211;2600 Ma (25%). The ca. 260&#8211;470 Ma are the age characteristics of Cambrian to Triassic subduction-related magmatic rocks in the Andean-type continental margin. The ca. 1700&#8211;2100 Ma and ca. 2200&#8211;2600 Ma aged detrital zircons compare well with age distributions for basement rocks of North China Craton. In summary, our provenance data converge to imply that the Carboniferous-Permian sediments in the central Ordos were related to the uplift and denudation of the Andean-type continental arc stretching across the northern margin of the North China Craton, which is directly related to the southward subduction of the Solonker Ocean in the southern branch of the Paleo-Asian Ocean. In addition, zircon U-Pb age distribution characteristics indicate that there is an obvious crustal thickening event that led to provenance uplift in continental arc at the end of the Permian, recorded by increasing amounts of Permian-age zircons in the Shiqianfeng Formation and a craton-wide sedimentary hiatus below the Shiqianfeng Formation. Also, this tectonic event was coeval with climatic transition from humid to arid since accumulation of the Shiqianfeng Formation, expressed in sedimentary assemblage by evolving depositional environment from coal-bearing tidal flat via deltaic, to red-color seasonal lake.