银额盆地西部蒙额地1井二叠纪叶肢介的发现及其意义

The discovery of Permian Estheria in the core of No. 1 Meng'edi well, western Yingen-Ejin basin, and its significance

近年来,银额盆地油气勘探不断取得新发现与突破,但对钻井地层划分及主要油气产层时代存在巨大争议,或认为产层为白垩系,或认为产层属二叠系。2017年实施的蒙额地1井钻井及取心工作,在930.5~958.0m井段的灰色、灰绿色粉砂质泥岩、泥岩层和1085.0~1095.5m井段的深灰色泥岩层中发现叶肢介化石。第一层段叶肢介为加氏圆通古斯卡叶肢介(比较种)Cyclotunguzites cf.gazimuri Novojilov,第二层段叶肢介为额济纳旗半圆李氏叶肢介(新种)Hemicycloleaia ejinaqiensis Niu(sp.nov.)和内蒙古点列叶肢介(新种)Polygrapta neimengguensis Niu(sp.nov.),均为晚二叠世代表性叶肢介。在此基础上,通过钻井地层对比,明确了银额盆地主要油气发现井的产层为二叠系。叶肢介具有重要的生物古地理指示意义,通过二叠纪叶肢介的区域分布与对比,结合银额盆地石炭纪—二叠纪地层层序分析,进一步限定了古亚洲洋的闭合时限为前石炭纪。

In recent years, the oil and gas exploration in Yingen-Ejin basin keeps achieving significant findings and breakthroughs.However, stratigraphic division of drill holes and corresponding age of oil and gas reservoir remain much controversial. Some researchers hold that the reservoir would be Cretaceous layers, some opponents raise the idea of Permian. For the purpose of constructing stratigraphic succession in such a basin, No.1 Meng'edi well was drilled and cored in western Yingen-Ejin basin. Within this well, Estheria fossils were found in 930.5~958.0 m section composed of gray to greyish green silty mudstone and mudstone layers, and in 1085.0~1095.5 m section composed of dark gray mudstone layers, respectively. Therefore, Estheria fossils in the former well section were identified as Cyclotunguzites cf. gazimuri Novojilov, whereas those in latter section were identified as Hemicycloleaia ejinaqiensis Niu(sp.nov.) and Polygrapta neimengguensis Niu(sp.nov.). All of these Estheria fossils were assigned to the period of Permian. In addition to the evidence of stratigraphic correlation between drilling wells, the age of oil and gas reservoir was judged as Permian layers.Besides, Estheria fossils contain great indicating meaning in paleobiogeography. Based on comparing the distribution of Permian Estheria as well as analyzing the Carboniferous-Permian succession of Yingen-Ejin basin, the closing time of Paleo-Asian Ocean has been further constrained to Pre-Carboniferous.