鄂尔多斯盆地西缘复杂构造带奥陶系克里摩里组白云岩成因探讨OA

[Objective]The dolomite in the Ordovician Kelimoli Formation of the complex tectonic zone along the western Ordos Basin margin is a high-quality reservoir for natural gas exploration.However,its genetic mechanism and the relationships among the sedimentary environment,multi-stage tectonic superimposition,and diagenetic alteration remain controversial,limiting effective guidance for oil and gas exploration.[Methods]To elucidate the genesis of this dolomite,a comprehensive analytical approach was applied,incorporating thin-section petrography,cathodoluminescence(CL),C-O isotopes,X-ray diffraction(XRD)ordering degrees,trace and rare earth element(REE)geochemistry,and Sr isotopes,integrated with regional tectonic evolution.[Results]Under CL,the dolomites generally exhibit weak dark-brown luminescence with distinct zonation,alongside authigenic quartz and saddle dolomite,indicating hydrothermal involvement and multi-stage recrystallization during deep burial.Carbon and oxygen isotopic signatures further support a burial origin.XRD data reveal a relatively low ordering degree in dolomites,which decreases with increasing temperature,suggesting rapid crystallization under elevated temperatures.REE patterns display positive Ce and Eu anomalies,indicating that dolomitization occurred in a relatively closed,high-temperature,and high-pressure diagenetic system via internal fluid readjustment and material redistribution.Overall,the dolomite shows a relatively low degree of order,and the order decreases with higher temperatures,suggesting that the dolomite formed in an environment with relatively high temperature and rapid crystallization rate.Geochemically,lower Sr contents correlate with higher Fe and Mn concentrations,reflecting multi-stage superimposed alteration under deep burial conditions.Furthermore,strontium isotope values of medium-to coarse-grained dolomite closely approach average crustal values,likely influenced by crustal Sr transported along coeval tectonic conduits.[Conclusions]This research attributes the dolomite formation primarily to deep burial and the coeval superimposition of tectonic fluid modification.The origin and evolution of the Ordovician Kelimoli Formation dolomite were strongly controlled by deep fault systems.During the co-deposition period,this fault system controlled the development of high-energy terraces.In the subsequent tectonic activity phase,the deep fault system became a fluid migration channel,facilitating the superimposed modification of dolomite bodies.[Significance]The research results provide fundamental support for the efficient exploration of oil and gas resources.