湖北秭归地区震旦系灯影组白云岩地球化学特征及其成因意义

白云岩化流体性质与成岩作用是近年来碳酸盐岩成岩作用研究的热点,研究白云岩的成因有利于进一步认识白云岩储层的形成机制并为优质储层的预测提供依据。通过岩石学、矿物学(X射线衍射)、地球化学(微量元素、稀土元素、碳氧同位素)方法,系统研究湖北秭归地区灯影组不同类型白云岩的成因,并分析了可能的白云岩化模式。样品的微量元素特征显示,秭归地区白云岩未受到陆源碎屑物质的影响,形成于气候干旱、海水咸度较大且氧化的沉积环境中;Sr含量特征显示白云岩发生了较为彻底的白云岩化,其成岩环境为温度较高的埋藏环境,成岩过程中未受到淋滤作用的影响;秭归地区白云岩化流体主要来源于海水。结合蒸发白云岩(萨布哈)及埋藏白云岩化模式解释了秭归地区泥微晶白云岩及晶粒白云岩的形成过程。

Geochemical Features and Genesis of Dolomite in Sinian Dengying Formation of Zigui Area,Hubei Province

Fluid properties of dolomitization and dolomite diagenesis is a hotspot of carbonate diagenesis research in recent years.It is very important to study the genesis of dolomite and to understand the formation mechanism of dolomite reservoirs,which can be used to predict high-quality reservoirs.In this paper,the genesis of dolomites in Dengying Formation in Zigui County has been studied systematically via petrological,mineralogical(X-ray diffraction),and geochemical(trace elements,REEs and carbon-oxygen isotopes)analyses,and possible dolomitization patterns were inferred.According to the trace element characteristics,the Zigui dolomites had not been affected by terrigenous debris,and were formed in an arid,highly-saline seawater and oxidizing environment.The Sr contents show that the dolomites have been completely dolomitized,and the diagenetic environment was likely a high-temperature burial one with no effect of syn-diagenetic leaching.The dolomitized fluids were mainly derived from seawater.Based on the results above,we proposed the evaporite dolomite(Sabuha)and burial dolomitization models to account for the formation of mud microcrystalline dolomite and crystalline dolomite in Zigui area.