摘要：

早奥陶世马家沟期，在鄂尔多斯东部的陕北地区沉积了近千米厚的碳酸盐岩－蒸发岩地层。运用微相分析的方法，对这套地层进行了矿物岩石学、古生物学、沉积动力特征及形成环境的分析。按矿物组成、微观结构、组构和生物化石（及其碎屑）的组成等特征，把该区碳酸盐岩－蒸发岩划分为18个典型的微相类型。又根据其成因概括为6个微相系列，即与开阔海环境有关的微相系列、与滩相沉积有关的微相系列、与生物礁(丘)有关的微相系列、与隐藻席有关的微相系列、与局限－强烈蒸发条件有关的微相系列、次生晶粒结构微相系列。各系列的微相类型具有相近的成因环境特征，且微相的变化表现为相对的连续性。微相研究结果还表明，该区马家沟组的石灰岩类微相主要形成于开阔海陆棚环境和潮坪环境，部分与生物礁的发育有关；硬石膏岩、石盐岩等蒸发岩类微相主要形成于蒸发盆地与外海周期性隔绝的干化蒸发条件下；白云岩类微相有两种成因类型，即萨布哈环境的准同生白云岩化作用和埋藏成岩环境的成岩白云岩化作用。

Abstract:

During the Early Ordovician, a suit of carbonate-evaporites had deposited in the east part of the Ordos, which is now known as the Majiagou Formation and up to approximately 1000 meters in thickness.The rocks of the Majiagou Formation can be classified into 18 types of microfacies according to the mineral composition, microscopic structure and fossils. These microfacies types can be grouped into 6 series genetically, which are open sea-related microfacies series, grain-shoal-related microfacies series, secondary crystalline granular textural microfacies series, reef (mound)-related microfacies series, cryptalgal mat-related microfacies series and restricted-intense evaporation-related microfacies series. The microfacies in each series are similar in genesis and environments of formation, and their shifts are relatively continous.The results of microfacies analysis indicate that: (1) most of the limestones of the Majiagou Formation formed in open sea shelf environments and tidal flat environments, and part of them was related to the development of reefs; (2) the evaporites, such as anhydrites and halite, had formed under the condition of evaporation, because of the saline depression's periodic isolation from the open sea; (3) the dolomites have 2 genetic types: one related to sabkha environments and another related to diagenetic environments during buring.