川东南寒武系娄山关群白云岩成岩作用特征

Diagenetic characteristics of dolomites in the Cambrian Loushanguan Group in southeastern Sichuan Basin

通过对川东南寒武系娄山关群两剖面(京竹和中坝)的白云岩及后期充填物的岩石学、碳氧同位素和阴极发光特征综合研究,系统分析了娄山关群白云岩成岩作用类型及特征,其主要的成岩作用类型包括白云岩化作用、溶蚀作用、胶结作用和硅化作用等,认为白云岩成因有4种:准同生、回流渗透、埋藏和热液白云岩化作用。并将成岩作用阶段划分为准同生、早成岩、晚成岩和表生成岩等4个阶段。同时,分析了成岩演化的影响因素及其对孔隙发育的影响,其成岩演化主要受到沉积环境、沉积物原始结构特征和沉积旋回等因素的影响。形成于潮坪潟湖环境的泥微晶白云岩,原始孔隙不发育,受后期成岩流体改造较弱,孔隙不发育;形成于滩相环境的颗粒白云岩和晶粒白云岩,原始孔隙较发育,后期成岩流体改造较强,孔隙发育,可以作为良好的油气储集层。

Based on the comprehensive studies of petrology,carbon and oxygen isotopes,and cathodoluminescence characteristics,it has been shown that dolomites from the Jingzhu and Zhongba outcrop sections of the Cambrian Loushanguan Group have experienced multiple diagenetic effects such as dolomitization,dissolution,cementation and silicification. There are four types of dolomite： penecontemporaneous,seepage refluxing,buried,and hydrothermal. Four diagenetic stages were divided into penecontemporaneous,early,late and epidiagenetic. The influencing factors of diagenetic evolution and pore development were analyzed. Diagenetic evolution was mainly affected by the sedimentary environment,the original structure of sediments and sedimentary cycles.Micrite dolomites formed in tidal flat and lagoon environments have a poor original porosity,and the late diagenetic fluid alteration was weak. Grain dolomites and crystalline dolomites formed in a beach environment have lots of primary pores,and their porosity was further improved by late diagenetic fluid alteration. As a result,they are more favorable reservoirs for oil and gas.