鄂南三叠系延长组自生成岩矿物成因及期次

The Genesis and Period of Authigenic Diagenetic Mineral in Triassic Yanchang Formation, the Southern Ordos Basin

为弄清鄂尔多斯盆地南部三叠系延长组关键成岩矿物形成的时间与过程,通过对自生矿物之间的产状及其与其他矿物互生关系的镜下观察,并利用流体包裹体、碳酸盐碳氧同位素记录的成岩流体信息,深入讨论了盆地南部自生成岩矿物成因及期次。研究认为,泥微晶方解石、菱铁矿和白云石(旬邑地区)为成岩早期沉淀的矿物,其中,菱铁矿的形成时间早于自生绿泥石包膜;泥微晶方解石沉淀时间与菱铁矿大致同期;旬邑地区白云石胶结物与北部物源区的泥微晶方解石和菱铁矿胶结物的形成同期;中晚期亮晶方解石和铁方解石等的形成时间整体早于白云石和铁白云石。石英次生加大边的两个世代分别对应90.0~100.0℃和110.0~120.0℃;自生微晶石英生长的时间略早于或同时于自生绿泥石的形成时间。自生绿泥石包膜主要形成于成岩早期,一般呈两个世代生长,第一世代自生绿泥石形成于20.0~50.0℃,以颗粒绿泥石环边赋存状态为主;第二世代形成于部分机械压实作用以后,只生长于孔隙接触的颗粒表面或第一世代绿泥石形成的微晶石英晶体表面,形成温度约为50.0~70.0℃。研究区延长组自生伊利石的分布较为广泛,其形成具有多源性的特点。

In order to understand the time and process of diagenetic mineral formation in the Triassic Yanchang Formation in the southern Ordos Basin,the occurrence of authigenic minerals and their alternative relationship with other types of minerals are examined.Furthermore,the liquid information of diagenetic minerals is recorded using fluid inclusion and the oxygen isotope data of carbonates.Based on these findings,the genesis and period of authigenic diagenetic minerals in the southern part of the Ordos Basin is discussed in detail.The study shows that mud-microcrystalline calcite,siderite,and dolomite(Xunyi Area)are diagenetic minerals precipitated at the early stages.Among these minerals,siderite is formed earlier than the authigenic chlorite coating,while the mud-microcrystalline calcite is formed at approximately the same time with siderite.The dolomite cement found in the Xunyi Area is formed at the same time with the mud-microcrystalline calcite and siderite found in the north source areas.The mid-late stage sparry calcite and ferroan calcite are both formed earlier than the dolomite and ferroan dolomite.The two generations associated with quartz secondary enlargement corresponds to 90.0~100.0℃and 110.0~120.0℃,respectively.The growth period of authigenic microcrystalline quartz is slightly earlier than or the same as the formation time of authigenic chlorite.The authigenic chlorite coating is formed during early diagenesis,which often grows in two generations.The authigenic chlorite in the first generation is formed at 20.0~50.0℃and mainly exists in the form of ring-edge occurrence of chlorite particles.The second generation authigenic chlorite,formed by compaction,is found to only grow on the particle surface in contact with the pore,or the surface of microcrystalline quartz crystals formed from the first-generation chlorite.The formation temperature of the second generation authigenic chlorite is around 50.0~70.0℃.The authigenic illite is found to be widely distributed in the Yanchang Formation in the research region.The authigenic illite is formed from multiple sources.