藏北日土地区南羌塘地块晚石炭—早二叠世海相裂谷盆地沉积序列:冈瓦纳大陆北缘初始裂解的沉积响应OA北大核心CSTPCD

The South Qiangtang Block(SQB)is widely acknowledged as part of the Cimmerian Continent,which rifted away from the northern Gondwana margin during the Early Permian,marking the initial opening of the Bangong-Nujiang Meso-Tethys Ocean.However,the sedimentary response to this rifting event remains unconfirmed,leaving the event ambiguous.In this study,five sedimentary successions are identified in the Rutog area,Northern Xizang,each characterized by distinct facies that record different stages in the tectonic evolution and climatic influences on the basin,along with associated changes in the rates of basin subsidence and sediment accommodation.Succession Ⅰ,formed in the Late Carboniferous to Asselian age,shows that glaciomarine sediments compensated for the sediment accommodation generated by the basin subsidence,resulting from tectonic activities and climatic factors in the early stage of the syn-rift.During the Sakmarian to early Artinskian age,the glaciomarine retrogradational sequence represented by the Zhanjin Formation(Succession Ⅱ)and the following progradational-aggradational sequences represented by the Qudi Formation(Succession Ⅲ)mark the climax and standstill stages of the first episode of the syn-rift tectonic activities,respectively.In the late Artinskian to Kungurian age,the second episode of syn-rift is manifested by the Succession Ⅳ and Ⅴ.And the former retrogradational sequence(Succession Ⅳ),reflected in the lower part of the Tunlonggongba Formation,indicates a climax stage of syn-rift tectonic activity,while the latter aggradational-progradational sequences(Succession Ⅴ),represented by the upper part of the Tunlonggongba Formation,mark a stage of tectonic quiescence.Therefore,these Early Permian sedimentary successions in the SQB are best explained by the tectonic subsidence resulting from the rifting of the SQB from the Gondwana margin,suggesting an early Permian timeline for the initial opening of the Bangong-Nujiang Meso-Tethys Ocean.