鄂尔多斯盆地中东部米脂地区奥陶系马五5亚段叠层石白云岩特征及其地质意义

鄂尔多斯盆地中东部米脂地区马五5亚段底部发育一套叠层石白云岩,是研究微生物岩及微生物白云岩化作用的良好素材.通过岩石学、矿物学、阴极发光、扫描电镜、碳氧锶同位素及地球化学等分析,对米脂地区奥陶系马五5亚段叠层石白云岩进行了研究,确定了马五5亚段沉积环境,并探讨了该套叠层石白云岩的成因及其地质意义.研究结果表明:①研究区...

Characteristics and geological significance of stromatolite dolomite of Ma 55 submember of Ordovician Majiagou Formation in Mizhi area,central-eastern Ordos Basin

A set of stromatolite dolomite developed at the bottom of Ma 5₅ submember of Majiagou Formation in Mizhi area,central-eastern Ordos Basin,which is a good material for studying microbial rocks and microbial dolomitization.The stromatolite dolomite was studied through the analysis of petrology,mineralogy,cathodoluminescence,scanning electron microscope,carbon,oxygen and strontium isotopes,geochemistry,the sedimentary environment of Ma 5₅ submember was determined,and the genesis and geological significance of this set of stromatolite dolomite were discussed.The research results show that:(1)The stromatolites in the study area can be divided into columnar and dendritic according to the morphological characteristics,the dolomite crystal is microcrystalline,and it is dark red in the cathodoluminescence,and the dolomite is granular under the scanning electron microscope.(2)Theδ¹³C value of stromatolite dolomite(-4.15‰--0.80‰)is generally within the range of seawater value in the same period,and theδ¹⁸O value(-13.19‰--6.62‰)is obviously negative compared with the seawater value in the same period.The ⁸⁷Sr/⁸⁶Sr value(0.7089-0.7098)is higher than that of seawater in the same period.The contents of Fe,Mn,Na of the stromatolite dolomite are relatively high,and the Sr content is relatively low.The dolomitization fluid of the stromatolite dolomite of Ma 5₅ submember in the study area is mainly marine-derived fluid,mixed with atmospheric fresh water,which is the product of shallow buried infiltration and reflux in the intertidal-subtidal zone.(3)The intertidal zone with seawater salinity conversion in the early stage of transgression is a favorable area for oil and gas exploration of stromatolite dolomite.