上黑龙江盆地中上侏罗统二十二站群的地层划分与时代

Stratigraphic division and age of the Mid-Upper Jurassic Ershi'erzhan Group in the upper Heilongjiang River basin

根据1∶5万区域地质调查,大兴安岭北端上黑龙江盆地内的原中侏罗统二十二站组的时代被重新厘定为中、晚侏罗世Bajocian─Tithonian期并改称为二十二站群。根据岩性特征和化石组合,将其进一步划分为两个组:下部称大西尔根气河组,其下部岩性以砂岩为主,上部以泥质粉砂岩─砂岩为主,含中侏罗世至晚侏罗世早期的双壳类动物群化石,可划分为Sibireconcha─Cuneopsis,Margaritifera─Unio,Fergannoconcha3个生物组合;上部称马林组,主要由粉砂岩组成,夹有少量砾岩和粉砂质灰岩,含晚侏罗世中晚期的介形类动物群化石,可称为Eoparacypris─Rhinocypris─Yanshanina组合。

Based on the1∶50000regional geological survey the age of the original Middle Jurassic Er-shi'erzhan Formation in the upper Heilongjiang River basin at the northern end of the Da Hinggan Moun-tains is determined to be Mid-Late Jurassic Bajocian-Tithonian and renamed the Ershi'erzhan Group.Ac-cording to the lithological features and fossil assemblage,this group may be further divided into two for-mations.The lower formation,called the Daxi'ergenqihe Formation,consists dominantly of sandstone in the lower part and muddy siltstone-sandstone in the upper part and contains fossils of a Middle to early Late Jurassic bivalve fauna which is divisible into the Ferganoconcha,Margaritifera-Unio and Sibireconcha-Cuneopsis assemblages.The upper formation,called the Malin Formation,is composed mainly of siltstone with minor amounts of conglomerate and silty limestone and yields the mid-late Late Jurassic ostracod as-semblage Eoparacypris-Rhinocypris-Yanshanina.