The Age Re-Determination of the Dibucuo Formation in Cuoqin Area,Xizang

Liu Han; Li Jun; Gao Rui; Gou Zhengbin; Zhang Shizhen

doi:10.3799/dqkx.2023.086

Abstract：The Upper Permian Dibucuo Formation in Cuoqin area is subject to age redetermination to accurately understand its geological significance since it is contradicted by the research progress of regional paleontology and stratigraphy. Based on field survey,regional stratigraphic correlation and detrital zircons U-Pb dating,the Dibucuo Formation is reclassified into three lithostratigraphic units of different ages. The Dibucuo Formation A is characterized by conglomerate-bearing sand-slate and Late Paleozoic plant fossils,and similar clastic zircons age spectrum with the Laga Formation,which should be classified into Laga Formation or Angjie Formation. Dibucuo Formation B is mainly composed of marine-continental clastic rocks,which is determined as the lower part of the Lower Cretaceous Zenong Group according to the Early Cretaceous clastic zircons and its emplacement by Early Cretaceous intrusive rocks. Dibucuo Formation C is almost completely composed of the late Early Cretaceous volcanic and pyroclastic rocks,consistent with the upper part of the Lower Cretaceous Zenong Group. Combined with the regional data,it is believed that the Cuoqin area was a continuous carbonate deposit from the Middle Permian to the Late Triassic,which was not affected by the Late Paleozoic Gangdese island arc orogenesis. The Early Cretaceous southern boundary of Bangongco-Nujiang residual sea basin in Cuoqin area is pushed about 50 km southward compared with the previous understanding.