吕梁古隆起对鄂尔多斯盆地马家沟组沉积的控制作用: 基于陕西府谷剖面^*

Control of Lüliang paleo-uplift on deposition of the Ordovician Majiagou Formation in Ordos Basin: evidence from Fugu outcrop in Shaanxi

摘要

中奥陶世马家沟组沉积时期,鄂尔多斯局限海周缘分布着一系列古隆起,其中吕梁古隆起对马家沟组沉积的控制作用研究相对薄弱,制约了对鄂尔多斯盆地东北部马家沟组沉积环境的认识。通过对陕西府谷剖面实测和采样,结合鄂尔多斯盆地北部的钻井、取心资料,分析了马家沟组的厚度、岩相类型及沉积微相变化,总结出吕梁古隆起对马家沟组沉积的控制作用。控制作用主要表现为: (1)吕梁古隆起的间歇性活动阻隔了鄂尔多斯局限海与华北广海的海水循环; (2)高海平面期,吕梁古隆起位于水下,对海水的阻隔作用弱,且古隆起区为开阔海灰坪,古隆起以西地层厚度变化较小,形成灰坪和云坪的沉积分异; (3)低海平面期,吕梁古隆起间歇性暴露,海水循环被明显阻隔,且古隆起区为潮间—潮上带的泥云坪,向东地层厚度减小,过渡为灰坪,而向西地层厚度迅速增加,形成泥云坪、膏云坪、膏盐湖的沉积分异。该研究成果为鄂尔多斯盆地北部马家沟组的沉积学研究提供了相关的岩石学和古环境方面的证据。

Abstract

During deposition of the Middle Ordovician Majiagou Formation,a series of paleo-uplift was discovered around the Ordos restricted sea. It remains relatively poorly studied as to how Lüliang paleo-uplift controlled deposition of the Majiagou Formation,which restricted understanding of sedimentary environments of the Majiagou Formation in the northeastern part of the basin. Through detailed measurement and sampling analysis of the Fugu outcrop in Shaanxi Province,combined with the drilling and core data,stratigraphic thickness,lithofacies and microfacies of the Majiagou Formation were studied. Lastly,controls of the Lüliang paleo-uplift on deposition of the Majiagou Formation are discussed. The research results show that: (1)the Lüliang paleo-uplift intermittently blocked the seawater circulation between the Ordos restricted sea and the North China sea. (2)The paleo-uplift was located underwater during the high sea level period,and the barrier to seawater circulation was weak;the stratal thickness in the west of the paleo-uplift has little variation;the underwater paleo-uplift formed a limestone flat,and limestone flat and limestone/dolomite flat formed in the west of the Lüliang paleo-uplift. (3)During the low sea-level period,the paleo-uplift was intermittently subaerially exposed,and obviously blocked circulation of seawater between the Ordos restricted sea and North China sea;the stratal thickness decreases in the east of the paleo-uplift,and sedimentary facies changes from muddy dolomite in the paleo-uplift to limestone in the east of the paleo-uplift. The stratal thickness increases significantly to the west of the paleo-uplift,forming argillaceous dolomite flat,gypsum dolomite flat,and gypsum and saline lacustrine facies. The study provides petrological and paleo-environmental evidence for the Majiagou Formation in the eastern part of the basin.

关键词

吕梁古隆起 / 古岩溶 / 白云岩 / 马家沟组 / 鄂尔多斯盆地

Key words

Lüliang paleo-uplift / paleokarst / dolostone / Majiagou Formation / Ordos Basin

基金资助

*中国石化科技攻关项目(编号: P20043-2)资助