鄂尔多斯盆地南缘平凉组烃源岩沉积环境与地球化学特征

Sedimentary environment and geochemical characteristics of hydrocarbon source rocks in the Pingliang Formation,southern margin of the Ordos Basin

倪春华，周小进 王果寿，刘运黎，杨帆

鄂尔多斯盆地南缘地区发育中奥陶统平凉组烃源岩。在对采集于该地区的5条剖面、40余件露头样品测试的基础上，利用微量元素分析了该地区中奥陶世平凉期的古盐度、水动力条件和氧化还原条件，认为当时主要发育微咸水-半咸水、弱水动力条件、还原性的深水斜坡相和咸水、强水动力条件、偏氧化-弱还原性的碳酸盐岩台地相两种古沉积环境，且前者为烃源岩发育的有利区。通过对有机碳含量、有机质类型和成熟度的综合评价，认为鄂尔多斯盆地南缘平凉组烃源岩主要为集中于下部的泥岩，具有厚度大、有机碳含量高、有机质类型好（以腐泥型为主）及热演化程度高（主体处于成熟晚期-高成熟期）的特点，为中等-好气源岩。综合研究认为,渭北隆起北部是鄂南地区下古生界勘探的有利地区。

Hydrocarbon source rocks were developed in the Pingliang Formation of the Middle Ordovician in southern Ordos Basin. Based on test of over 40 outcrop samples from five sections in southern Ordos Basin, we studied the paleosalinity, hydrodynamic conditions and redox conditions during the Pingliang Age of the Middle Ordovician through trace element analysis. Two major paleosedimentary environments are identified: deepwater slope with brackish, weak hydrodynamics and reducing conditions; and carbonate platform with brine, strong hydrodynamics and oxidizingprone and weak reducing conditions. The former was favorable for development of quality hydrocarbon source rocks. By conducting a comprehensive evaluation of the TOC, organic types and maturity, we come to the conclusion that the mudstone at the lower part of the Formation is the major source rocks, which are mediocre to excellent gas source rocks featuring in large thickness, high TOC, favorable kerogen types (sapropeltype predominant) and high maturity. It is therefore suggested that the northern Weibei high be favorable for exploring the lower Paleozoic in southern Ordos Basin.

10.11743/ogg20110105