鄂尔多斯盆地中三叠统与上三叠统地层界线讨论  

Discussion on the Stratigraphic Boundary between Middle Triassic and Upper Triassic

作　　者：邓秀芹[1,2] 李文厚[1] 刘新社[1,2] 庞锦莲[2] 刘鑫[2] 

机构地区：[1]西北大学地质系,西安710069 [2]中国石油长庆油田分公司勘探开发研究院,西安710018

出　　处：《地质学报》2009年第8期1089-1096,共8页Acta Geologica Sinica

基　　金：国家科技重大专项"大型油气田及煤层气开发"(编号2008ZX05044);国家重点基础研究发展计划"973"项目(编号2003CB214602)资助成果

摘　　要：针对延长组地层划分的争议,开展了延长组孢粉组合、岩石学特征、湖盆演化规律等对比分析,结果显示长8—长10油层组与长1—长7油层组差异显著。其中,长8—长10油层组沉积期,地势平坦,河流、三角洲和滨浅湖广泛发育,岩石成分成熟度低,孢粉组合中蕨类植物孢子占优势,中三叠世的重要分子Punctatisporites、Verrucosisporites含量较高;长7油层组沉积期深湖范围宽广,盆地西南、西部地区长7油层组砂岩中石英含量明显提高,岩石类型发生较大的改变,西缘和西南缘沉积体系也由辫状河、辫状河—三角洲体系演化成冲积扇、扇三角洲沉积体系,该段地层孢子花粉含量相近,以具有晚三叠世色彩的Duplexisporites大量出现为特征。此外,在盆地西部、西南及湖盆中部地区,长7油层组底部稳定分布的一套凝灰岩薄层,记录了同期的火山、岩浆活动等地质事件,为早印支运动的重要表现形式,因此长7与长8油层组之间地层界线为中三叠统与上三叠统界线。Considering the dispute over the Yangchang Formation classification, a comparative analysis and investigation was conducted. Sporo-pollen assemblage, petrologic characteristics and basin evolution all suggest the distinct differences between the ChS--Ch10 oil-bearing formations and Chl-Ch7 oil bearing formations. Sedimentary period of Ch8--Ch10 oil-bearing formations is characterized by even landform, well developed rivers, deltas and shallow lakes, and low sandstone maturity. Analysis on the samples from the Ch8--Ch10 strata shows that the sporo-pollen is dominated by pteridophyta spore, with high content of Punctatisporites one of the significant members of sporo-pollen living in middle Triassic up to 50.5%. However, the deep lake widened expeditiously at the beginning of the Ch7 depositional period. The quartz content in the Ch7 sandstone increases significantly, resulting in the corresponding change of rock types in the west and the southwest. Therefore, the sedimentary system in the west and southwest margins of the basin are evolved into alluvial fan and fan delta from braided channel and braided channel/delta system. The biotic community is characterized by the appearance of Duplexisporites-an important member of sporopollen assemblage in late Triassic. In addition, a suit of tufts distributed at the bottom of Ch7 in the western, southwestern and central parts of the basin records geological events such as syn-depositional volcanism and magmatic activities, which are the important features of early Indo-Sinian movement. Consequently, the stratigraphic boundary between Ch7 and Ch8 oil bearing formations can be regarded as the boundary between mid-Triassic and upper Triassic as well as the representative of the first episode of the Indo-Sinian Movement.

关 键 词：延长组时代归属 孢粉组合 沉积演化 凝灰岩 中、上三叠统 地层界线 

分 类 号：P618.13[天文地球—矿床学]