西秦岭岷江流域三叠系的划分

THE STRATIGRAPHIC DIVISION OF THE TRIASSIC IN THE MINJIANG RIVER VALLEY IN THE WESTERN QINLING MOUNTAINS

作者根据在甘肃省宕昌县及岷江一带,进行1:5万区域地质调查研究成果,将该区三叠系自下而上划分为五个组.下部称仇家山组,以白云岩、白云质灰岩为主,虽未获古生物化石,但按岩性及层位与四川省若尔盖及甘肃迭部一带的马热松多组相当,时代为早三叠世晚期的奥伦尼阶。中部郭家山组以灰岩夹砂岩,页岩组成,产丰富的腕足、瓣鳃、腹足及牙形刺化石,其时代属中三叠世早期的安尼阶。上部依次为滑石关组、大河坝组、下马龙组,它们分别以灰岩、石英砂岩、泥灰岩为主,在后二个组中产植物及孢粉等,它们的时代大致属中三叠世拉丁阶沉积.

On the basis of the results of 1:50000 regional geological surveys,the Triassic distributed in the Minjiang River valley in Yanchang County,Gansu Province,may be divided from below upwards into five formations.The lower part is called the Choujiashan Formation,consisting mainly of dolomite and dolomitic limestone.Although no fossils have been collected yet,it may be stratigraphically and lithologically correlated with the Maresongduo Formation in Zoige of Sichuan Province and Tewo of Gansu Province,and its age may be assigned to the Olenekian Stage (late Early Triassic).The Guojiashan Formation in the middle is composed of limestone with sandstone and shale,yielding abundant fossils of brachiopods,lamellibranchs,gastropods and conodonts,and its age is considered to be Anisian (early Middle Triassic).Theupper part is successively represented by the Huashiguan,Daheba and Xiamalong Formations, dominated respectively by limestone,quartz sandstone and marls.The last two formations yield plant fossils and sporopollen and their age is assigned to the Ladinian Stage (Middle Triassic).