鄂尔多斯盆地马家沟组碳酸盐岩-膏盐岩共生体系沉积微相与沉积模式^*

Microfacies and depositional model of a carbonate-evaporite symbiotic system of the Majiagou Formation in Ordos Basin

摘要

碳酸盐岩-膏盐岩共生体系是化学沉积分异作用形成的岩石共生组合,对其进行微相分析和沉积模式构建,有利于揭示蒸发环境下的沉积学信息,对油气勘探具有指导意义。依据鄂尔多斯盆地奥陶系马家沟组大量钻井、岩心资料,开展岩石宏观、微观观察,识别沉积微相,分析沉积序列,构建沉积模式。结果表明: 马家沟组碳酸盐岩-膏盐岩共生体系可划分出10类微相(MFT1-MFT10): 盐岩、膏岩、含膏云岩、纹层状微粉晶云岩、颗粒云岩、粉—细晶白云岩、微生物云岩、生物扰动(灰)云岩、纹层状微晶灰岩、微晶颗粒灰岩; 共生体系发育4类微相组合: (1)潮间上带—潮上带白云岩-含膏云岩-泥云岩组合; (2)潮间下带膏岩-藻云岩-白云岩组合; (3)潮下带纹层状灰岩-搅动灰岩-扰动灰岩组合;(4)潟湖内层状膏岩-团块状膏岩-盐岩组合。马家沟组为浅盆蒸发成盐,低海平面蒸发成盐,高海平面发育碳酸盐岩,海平面反复波动形成巨厚碳酸盐岩—膏盐岩共生组合。

Abstract

The carbonate-evaporite symbiotic system is a rock symbiotic association formed by chemical depositional differentiation. Microfacies analysis and sedimentary model construction of such a system are conducive to revealing the sedimentary information that have guiding significance for oil and gas exploration in evaporatic environments. Based on a large number of borehole data of the Majiagou Formation in Ordos Basin,macro-and microscopic observation of the rocks was carried out to identify sedimentary microfacies,analyze sedimentary sequence,and construct sedimentary model.The results show that there are ten types of sedimentary microfacies(MFT1-MFT10)in the carbonate-evaporite symbiotic system of the Majiagou Formation: halite,gypsum,gypsum-bearing dolomite,laminated dolomite,crystalline dolomitic grainstone,microcrystalline dolomite,microbial dolomite,bioturbated dolomite,laminated limestone,crystalline grainstone. four types of sedimentary sequence are developed in the symbiotic system: (1)upper intertidalto supratidal dolomite-gypsodolomite-argillaceous dolostone;(2)lower intertidal evaporite-algal dolomite-dolomite;(3)subtidal laminated limestone-churned limestone-bioturbation limestone;(4)lagoonal laminated evaporite-lumpy evaporite-salt rock. Evaporites of the Majiagou Formation were formed during the shallow basins period and low sea level period,while carbonates were formed during the high sea level period.The giant carbonate-evaporite symbiotic system formed through repeated fluctuations in sea level.

关键词

微相 / 生物扰动云岩 / 微生物云岩 / 沉积模式 / 马家沟组 / 鄂尔多斯盆地

Key words

microfacies / bioturbated dolostone / microbial dolostone / sedimentary model / Majiagou Formation / Ordos Basin

基金资助

*中国石油长庆油田分公司重大科技专项(编号: ZDZX2021)资助