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OA北大核心CSTPCD

The carbonate-evaporite symbiotic system is a rock symbiotic association formed by chemi-cal 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 explo-ration 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 mi-crofacies,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 do-lomitic grainstone,microcrystalline dolomite,microbial dolomite,bioturbated dolomite,laminated lime-stone,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 lime-stone;(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.