Establishment of the Middle—Upper Triassic Garezhadi Formation in the Coqen Block, Tibet
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摘要:
在西藏措勤断块新建了中三叠统—上三叠统卡尼阶岩石地层单位——嘎热扎地组。在建组剖面上，嘎热扎地组厚约485 m，下部岩性以碎屑岩为主，上部岩性为碎屑岩夹灰岩。嘎热扎地组与下伏上二叠统—下三叠统木纠错组、上覆上三叠统诺利阶麦龙岗组均为整合接触关系。该组尚未发现指示地层时代的化石，但前人在其下伏的木纠错组中发现了早三叠世牙形石，本次在其上覆的麦龙岗组发现7属8种珊瑚化石：Distichophyllia norica（Frech），Retiophyllia? sp.，Gablonzeria? sp.，Elysastraea juliana Turnšek，Volzeiasublaevis（Münster），Distichophyllia sp.，Guembelastraea? sp.和Beneckastraea baiyuensis Deng&Zhang。根据该组地层整合于两者之间，将其时代暂时限定为中—晚三叠世卡尼期。根据珊瑚化石、地层岩性特征及上下地层关系将研究剖面的地层进行了重新划分。嘎热扎地组的建立填补了措勤断块局限台地相三叠系序列中三叠统—上三叠统卡尼阶岩石地层单位名称的空白。嘎热扎地组建立以后，措勤断块局限台地相三叠系的岩石地层单位序列可以划分为上二叠统—下三叠统木纠错组，中三叠统—上三叠统卡尼阶嘎热扎地组，上三叠统诺利阶麦龙岗组，上三叠统瑞替阶—下侏罗统确哈拉组。这一序列的建立对于在措勤断块进一步识别出碳酸盐岩局限台地相三叠系，修订相关地区的地层认识具有指导作用。
Abstract: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.
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Key words:
- Tibet /
- Coqen Block /
- Garezhadi Formation /
- Middle—Upper Triassic /
- coral
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