鄂尔多斯奥陶纪马家沟期岩相古地理

在露头及钻井基干剖面的地层学及定量岩石学研究的基础上,采用单因素分析综合作图法,编制出了鄂尔多斯奥陶纪马家沟一期、马家沟二期、马家沟三期、马家沟四期、马家沟五期和马家沟六期的各种单因素图及岩相古地理图。在这种古地理图中,各级古地理单元的确定都有定量的单因素数据为依据。马一期、马三期、马五期的岩相古地理的特征相似,可概括为“陆外为坪,坪中有湖,坪外为海”和“湖中有膏,湖中有盐”;马二期、马四期、马六期的岩相古地理特征亦相似,可概括为“陆外有坪,坪外为海,海中为滩,海外为槽”。从马一期至马六期构成三个海侵海退旋回。当今陕北大气田的天然气主要赋存于马家沟五组的云坪相白云岩中,今后最有前景的天然气产层将是马家沟四组滩相白云岩。因此,鄂尔多斯奥陶纪岩相古地理研究有重要的地质意义和生产实践意义。

Lithofacies Paleogeography of Majiagou Age of Ordovician in Ordos Basin

Based on the study of stratigraphy and quantitative Sedimentology of eachfundamental sections,according to the “Single Factor Analysis and Comprehensive Mapping Method”,various single factor maps and quantitative lithofacies paleogeography maps of the Majiagou Age,i.e.Majiagou Age 1, Majiagou Age 2,Majiagou Age 3,Majiagou Age 4,Majiagou Age 5 and Majiagou Age 6 of Ordovician in Ordos,have been is studied and mapped.In these lithofacies paleogeography maps,the determination of paleogeographical units is based on quantitative single factor data.The features of the lithofacies paleogeograph of the Majiagou Age 1, Majiagou Age 3 and Majiagou Age 5 are similar,which can be summerized as “outside lands there were flats,in flats there were lagoons,outside flats there were open seas”and “in lagoons there were gypsum and salt”.The features of the lithofacies paleogeograph of the Majiagou Age 2,Majiagou Age 4 and Majiagou Aeg 6 are also similar,which can be summerized as “outside lands there were flats,outside flats there were open seas,in open seas there were banks,outside open seas there were troughs ”.Briefly,during the Majiagou Age there underwent three transgression-regression cycles.The reservoirs of the North Shaanxi Gas Field are the dolostones of the dolomitic flats in Majiagou 5,and the potential reservoirs will be the dolostones of the banks in Majiagou 4. Therefore,the study of the lithofacies paleogeography of Majiagou Age in Ordos has important significance in both geological theory and production.