靖边潜台南部奥陶系马家沟组古岩溶储层地球化学特征

鄂尔多斯盆地奥陶系马家沟组由于受加里东运动影响而隆起抬升遭受风化，其顶部形成了良好的岩溶油气储层。本文通过对可溶岩的溶蚀孔充填物、角砾间的胶结物和碳酸盐原岩进行δ13C、δ18O的分析，结果表明：（1）研究区的各类岩石的δ18O比奥陶纪海水的要偏负，而岩溶作用微弱的原岩其δ13C则与奥陶纪海水的相当；（2）随岩溶作用的加强，岩石中的δ13C、δ18O降低，且δ18O对岩溶作用反应更灵敏；（3）岩石溶孔中的充填物与原岩的δ13C和δ18O含量相当，表明其与原岩形成于同一流体源，应属同期沉积的岩溶产物，即形成于沉积物形成之后不久，成岩环境属于近地表环境。另外，通过对研究区各种岩石Sr含量的研究，以及Sr/Ca、Sr/Ba和B元素对成岩流体盐度的反应分析，结果显示研究区曾经有大量的淡水注入，低Sr含量和高Fe2+/Fe3+值则说明了沉积物曾经历过深部岩溶作用。

Geochemical characteristics of a paleokarst-reservoir in Ordovician Majiagou formation in southern Jingbian tableland

The nicer karst reservoirs were formed at the top of the Ordovician Majiagou formation in Ordos basin due to tectonic uplift and erosion during the Caledonian movement.Based on analysis of δ13Cand δ18Oin dissolution pore fillings,karst breccia cements and carbonate rocks,the results showed that,（1）The δ18Ovalue of various types of rocks is lower than that of the Ordovician seawater in study area while the δ13Cvalue of weak karstification original rock is similar to that of Ordovician seawater;（2） With intensified karstification,the δ18Oand δ13Cof rocks decreased,and the δ18Ovalue was more sensitive;（3）Fillings in dissolved pore and bedrock formed in the same fluid source,which should be the synsedimentary product of karst.In the paper,based on the values of Sr and the analytic of Sr/Ca,Sr/Ba and B elements which responded to the diagenetic fluid salinity,it may be concluded that there was a large freshwater input into the study area.The low Sr content and high Fe2＋）/ Fe~3＋ value illustrated that sediments had undergone burial karstification.