鄂尔多斯盆地西部马家沟期层序岩相古地理

针对鄂尔多斯盆地西部下奥陶统马家沟组Osq7、Osq8和Osq9层序，以体系域作为成图单元，采用体系域压缩法进行层序岩相古地理编图实践，研究鄂尔多斯盆地西部早奥陶世马家沟期层序岩相古地理的特征及演化。研究表明：下奥陶统地层主要由巨厚的海相碳酸盐岩和蒸发岩组成，可划分为19个三级层序，其中的马家沟组包含了8个三级层序，而且大多数属于Ⅱ型层序，主要由陆架边缘－陆架内低位、海侵、高位体系域构成。陆架边缘－陆架内低位域以中央古隆起出露海面成为规模较大的古陆为特色；海侵域以发育碳酸盐台地相以及出现碳酸盐陆棚、斜坡、海槽相为特征；高位域以云坪扩大、碳酸盐台地增生以及台内浅滩出现为典型特征。在盆地西部中央古隆起、贺兰拗拉槽等组成的古构造格局以及海平面升降变化的控制下，该区早奥陶世马家沟期层序岩相古地理总体上呈现出自西向东依次为海槽、斜坡、陆棚、台地/古陆、陆架内盆地边缘等错落有序的相带展布格局。

Sequence Lithofacies Paleogeography of Western Ordos Basin in Majiagou Stage,Ordovician

Lower Ordovician strata in western Ordos Basin are mainly composed of huge-thick marine carbonate and evaporite,and can be divided into 12 third order sequences,the Majiagou Formation,one of them,includes 8 third order sequences.These sequences mostly belong to TypeⅡsequence and are mainly consisted of shelf margin system tract（SMST）,intra-shelf lowstand system tract（ISLST）,transgressive system tract（TST）and highstand system tract（HST）.Mainly taking Osq7,Osq8,and Osq9 sequences in Majiagou Formation of Lower Ordovician as examples,system tract as mapping unit,sequence lithofacies paleogeographic maps of the early Ordovician Majiagou stage are mapped by adopting system tract compression method in western Ordos Basin.Characteristics and evolution of lithofacies paleogeography of the early Ordovician Majiagou stage are studied in western Ordos Basin.The SMST-ISLST are featured by the Central Paleouplift Zone becoming subaerial exposure and larger-scale paleo-land.The TST are characterized by the development of carbonate platform facies and the appearance of carbonate shelf,slope,and trench facies.The HST is typically featured by the enlarging of dolomite flat,accretion of carbonate platform and appearance of intra-platform shoals.Under the control of sea-level fluctuation and ancient tectonic framework which was consisted of the Central Paleouplift,Helangshan aulacogen,and others,the lithofacies paleogeographic framework of the early Ordovician Majiagou stage totally shows that successive distribution of trench,slope,shelf,platform/paleo-land,intra-shelf basin margin facies are orderly oriented in the direction from west to east in western Ordos Basin.