古地理格局对膏盐岩-碳酸盐岩共生体系沉积分异的控制--以鄂尔多斯盆地中东部奥陶系马家沟组五段6亚段为例

Control of paleogeographic pattern on sedimentary differentiation of evaporite-carbonate symbiotic system:A case study of the sixth sub-member of Ordovician Majiagou Formation M5 Member in central-eastern Ordos Basin,NW China

以鄂尔多斯盆地中东部奥陶系马家沟组五段6亚段(简称马五6亚段)为例,基于测井、录井、岩心和薄片等资料,研究古地理格局与膏盐岩-碳酸盐岩共生体系沉积分异的关系。结果表明:①在研究区内识别、细化出桃利庙西洼、桃利庙水下高地、桃利庙东洼、横山高地、东部盐洼、北部斜坡和西南部斜坡等7个次级地貌单元。②由西向东古地貌为“三洼两高”,“三洼”依次发育白云质局限潟湖、膏质蒸发潟湖、盐质蒸发潟湖,“两高”依次发育高能颗粒滩和微生物丘,南北两侧斜坡则发育环陆云坪。③古地貌格局造成来自西北侧祁连海补给海水的自然分异,控制白云岩、膏岩、盐岩共生体系由西向东的偏心式沉积分异,有别于经典的“牛眼式”和“泪滴式”干化收缩分布模式。④中祁连地块向华北板块碰撞俯冲,远端挤压应力传递形成马五6亚段沉积期的近南北向凹凸地貌格局。⑤桃利庙水下高地和横山高地马五6亚段发育南北向展布的丘滩有利相带,是勘探有利区,未来具有较大勘探潜力。

The relationship between paleogeographic pattern and sedimentary differentiation of evaporite-carbonate symbiotic system is examined based on logging,core and thin section data,by taking the sixth sub-member of fifth member of Ordovician Majiagou Formation(M56)in the central-eastern Ordos Basin as an example.(1)Seven sub-geomorphic units(Taolimiao west low,Taolimiao underwater high,Taolimiao east low,Hengshan high,East salt low,North slope and Southwest slope)developed in the study area.(2)The“three lows”from west to east developed dolomitic restricted lagoon,evaporite evaporative lagoon and salt evaporative lagoon sedimentary facies respectively,the"two highs"developed high-energy grain beach and microbial mound,and the north and south slopes developed dolomitic flats around land.(3)The paleogeographic pattern caused natural differentiation of replenishment seawater from the northwest Qilian sea,leading to the eccentric sedimentary differentiation of dolomite,evaporite and salt rock symbiotic system from west to east,which is different from the classic“bull's eye”and“tear drop”distribution patterns.(4)As the Middle Qilian block subducted and collided into the North China Plate,the far-end compression stress transferred,giving rise to the alternate highland and lowland in near north to south direction during the sedimentary period of M56 sub-member.(5)Taolimiao underwater high and Hengshan high developed favorable zones of microbial mounds and grain shoals in south to north strike in M56 sub-member,making them favorable exploration areas with great exploration potential in the future.