鄂尔多斯盆地南缘铜川地区三叠系延长组油页岩中“钙质结核”的成因初探

在鄂尔多斯盆地南缘铜川地区野外露头三叠系延长组长7段油页岩中发现了一些“钙质结核”，野外露头中呈层状发育于长7段油页岩中，形态为“透镜状”、“椭球状”、“飞碟状”，直径大小约为10～70 cm。为探明其岩石类型和主要岩石组分，运用显微镜薄片鉴定、电子探针实验、能谱分析等方法，对结核体进行岩石学特征分析。在此基础上，对其成因进行初步探讨。岩石学特征显示，霸王庄和宜君套滩剖面的“钙质结核”主要成分为重结晶方解石和晶粒方解石，具“球粒状”结构，岩石类型为灰岩；瑶曲聂家河剖面结核体主要岩石类型为泥-粉晶白云岩。分析认为这些“钙质结核”其野外产状和岩石成分，符合热水沉积碳酸盐岩和受热液活动影响的特征，并且铜川地区在长7期具备热液活动的条件。初步认为这些“钙质结核”为湖底热液活动成因的湖相碳酸盐岩。

A preliminary discussion on the origin of “calcareous concretion” in oil shale of Yanchang Formation in Tongchuan area,southern Ordos Basin

Some “calcareous concretion” were found in the oil shale of Chang 7 section of Yanchang Formation in the outcrops of the Tongchuan area, the southern part of the Ordos Basin. These “calcareous concretion” were layered developed in the oil shale of the Chang 7 section in the outcrops, in the form of “lenticular”,“ellipsoid”,“discoid”, about 10～70 cm in diameter. In order to identify the rock type and main rock components, the petrological characteristics of these concretion were analyzed by microscope observation of section, electron microprobe experiment and EDS analysis. On this basis, the origin of these “calcareous concretion” were preliminarily discussed. The “calcareous concretion” in Bawangzhuang and Taotan field section of Tongchuan area are mainly composed of recrystallised calcite and crystalline calcite, with “globular” structure, and its rock type is limestone. The rock type of “calcareous concretion” in Niejiahe field section are silt-micrite dolostone. The results show that these “calcareous concretion” in the field occurence and the composition of the rocks meet the characteristics of hydrothermal exhalative deposition of carbonate rocks and hydrothermal activities. And the Tongchuan area had the condition of hydrothermal activity in the Chang 7 period. It is tentatively believed that these “calcareous concretion” are lacustrine carbonate rocks that contribute to the hydrothermal activity.