Establishment of the Middle—Upper Triassic Garezhadi Formation in the Coqen Block, Tibet

A new lithostratigraphic unit in the Middle Triassic-Upper Triassic Carnian, the Garezhadi Formation, was established in the Coqen Block, Tibet.In the profile of the newly established lithostratigraphic unit, the Garizadi Formation is about 485 m thick.The lower lithology is dominated by clastic rocks, while the upper lithology is clastic rocks intercalated with limestone.It is conformable with both the overlying Upper Triassic Mailonggang Formation and the underlying Upper Permian-Lower Triassic Mujiucuo Formation.No fossils indicating the stratigraphic age have been found in it, but Early Triassic conodonts have been found in the underlying Mujiucuo Formation by previous work, and in our project, eight coral species belonging to seven genus were identified in the overlying Mailonggang Formation, including Distichophyllia norica (Frech), Retiophyllia? sp., Gablonzeria? sp., Elysastraea juliana Turnšek, Volzeia sublaevis (Münster), Distichophyllia sp., Guembelastraea? sp., Beneckastraea baiyuensis.According to its conformable contact with the underlying and overlying strata, the age of Garezhadi Formation is temporarily limited to the Middle-Triassic Late Triassic Carnian period.Moreover, the stratum observed in the measured profile was reclassified based on the age of corals, lithology and its contact relationships.The establishment of the Garezhadi Formation filled the naming blank of the lithostratigraphic units of the restricted platform facies of Triassic sequence in Coqen block.Its establishment resulted in the Triassic stratigraphic sequence of the restricted platform facies being divided into the Upper Permian-Lower Triassic Mujiucuo Formation, the Middle Triassic—Upper Triassic Carnian Garezhadi Formation, the Upper Triassic Norian Mailonggang Formation, the Upper Triassic Rhaetian-? Lower Jurassic Quehala Formation in asending order.The establishment of this sequence has a guiding role in further identifying the Triassic system of restricted carbonate platform facies and revising the stratigraphic understanding of related areas in Coqen block.