西藏昂仁县孔隆地区下拉组时代修订及其对冈底斯中晚二叠世沉积演化的制约

Age revision of the Xiala Formation in Konglong area,Nangren County,Tibet,and its constraints on the sedimentary evolution of the Gangdese belt in the Middle and Late Permian

冈底斯在晚二叠世是否隆升长期存在争议。通过详细的地层和古生物工作,报道了西藏昂仁县孔隆地区发现的连续海相沉积剖面,将下拉组分为2个岩性段,下部岩性以生屑灰岩和微晶灰岩为主,产珊瑚化石Wentzelella typica和Neokueichowpora gemina,■类化石Rugososchwagerina,Neoschwagerina sp.和Nankinella sp.,时代为中二叠世沃德期-卡匹敦期。上部岩性以硅质结核灰岩和结晶灰岩为主,在其中发现牙形石Neogondolella cf.leveni,Hindeodus typicalis,Clarkina orientalis,Clarkina longicuspidata等,时代为吴家坪晚期。将下拉组时代修订为中二叠世沃德期-晚二叠世吴家坪期,并推测其顶部的时代可能进入晚二叠世长兴期。认为冈底斯西部在中二叠世-晚二叠世为连续的海相沉积环境,中、晚二叠世之交不存在构造隆升事件。冈底斯西部在晚二叠世及三叠纪为古陆的观点,需要被重新考虑。

The existence of the uplift event in the Gondese belt during Late Permian is still long debated.On the basis of the detailed stratigraphic and paleontological works,this paper reports a continuous marine sedimentary section found in Konglong area,Nangren County,Tibet.The Xiala Formation is divided into two lithologic parts.The lower part mainly consists of bioclastic limestone and microcrystalline limestone,and the coral samples Wentzelella typical,Neokueichowpora gemina and fusulinid samples Rugososchwagerina,Neoschwagerina sp.,Nankinella sp.were found in this part.The age of the lower part of the Xiala Formation is the Middle Permian Wordian to Capitanian.The lower part mainly consists of nodular limestone and crystalline limestone.The conodont specimens found in this part are grouped into Neogondolella cf.leveni,Clarkina orientalis,Clarkina longicuspidata and Hindeodus typicalis,they are from the Wuchiapingian to Changhsingian.The age of the Xiala Formation was redefined to the Middle Permian Ward to Late Permian Wujiaping,and the age of the topmost part of the Xiala Formation may extend to Changhsingian stage.We conclude that the study area was a continuous marine depositional environment during the Middle Permian-Late Permian period,and there was no tectonic uplift event at the turn of the Middle Permian and the Late Permian.The view that western Gangdise was a land during the Late Permian and Triassic should be reconsidered.