Application of Evaporite Minerals in Identification of Marine Carbonate Sedimentary Environment: A Case Study of Ma 54 in the Central-East Ordos Basin
Abstract
Based on the lithological analysis and regional distribution, the genesis of gypsum-salt rock in Ma 54 in central-east Ordos Basin was studied, and then the reflected migration and evolution of the gypsum-salt rock and their sedimentary environment significance were discussed. The Ma 54 gypsum-salt rock was formed in the underwater concentration environment. The available drilling and coring data in the basin reveal that the Ma 54 gypsum-salt rock generally shows a trend of gradual thickening from west to east, and the occurrence and content of anhydrite show regular changes, which reflects the sedimentary environment information. Ma 54 belongs to the evaporation shelf environment with low sea level. According to the occurrence, content and distribution range of halite and anhydrite minerals, the evaporation shelf can be further divided into five kinds of microfacies. The evolution of sedimentary microfacies is controlled by sedimentary geomorphology features, ancient climate and relative sea level changes. In vertical direction, the sedimentary microfacies distribution has certain inheritance. However, as the slow transgression from Ma 543 to Ma 542 and then to Ma 541, sea water recharge rate and quantity increased, evaporation decreased, and sea water salinity gradually reduced, leading to regular changes of the development and distribution of the microfacies.
