The co-relationship of marine carbonates and evaporites: a study from the Tarim Basin, NW China
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ORIGINAL ARTICLE
The co‑relationship of marine carbonates and evaporites: a study from the Tarim Basin, NW China Xue Chen1,2 · Mingyang Wei1,2 · Xiaobo Li1,2 · Min Li1,2 Accepted: 7 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The coexistence of carbonates and evaporites is common for various petroliferous basins in geological periods globally. It holds much more significance to find out the interaction of these two. This paper expounds the macroscopical and microscopic relationship from petrography, facies, and geochemical analyses from core samples. The study area is dominated by successions of evaporites and carbonates, and three sulfate, five carbonates and mudstone lithofacies have been identified. And carbonates and evaporites are commonly lateral equivalents, both resulted from the similar sedimentary environment and chemical constituents. The intergrowth relationship was mainly reflected in the factors for their formation (including sea-level, evaporation, salinity, climate and so on), sedimentary cycle (including the vertical cycle and banded distribution) and the diagenetic transitions (including TSR, dolomitization, dedolomitization and dissolution). A depositional model has been developed that reveals a bull’s-eye pattern which was dominated by restricted carbonate platform and evaporitic platform with shoal and reef facies developed around the platform margins. With gypsum salts served as the caprock, favorable dolomite reservoir which largely resulted from the diagenetic transition and source of high quality can form a large reservoir. Keywords Carbonates and evaporites · Sedimentary cycle · Diagenetic transitions · Sedimentary model
Introduction Carbonates and evaporites are all the chemical sedimentary rocks and evaporites form by solar-driven concentration of a surface or nearsurface brine (Warren 2006). In terms of mineral composition, the main mineral components of the generalized evaporites include potassium, sodium, calcium, magnesium chloride, sulfate and carbonate, among which the alkaline–earth metal carbonates such as gypsum (CaSO4·2H2O), anhydrite ( CaSO4) and halite (NaCl) are the most important minerals (Zhu 2008; Warren 2016). Moreover, the associated evaporative carbonates, such as calcite (CaCO3) and dolomite (Ca(1 + x)Mg(1 − x)(CO3)2), among others. From the perspects of sedimentary geology, * Xue Chen [email protected] 1
College of Geosciences, China University of PetroleumBeijing, No. 18, Fuxue Road, Changping District, Beijing 102249, China
State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing, Beijing 102249, China
2
the evaporites we defined include not only autochthonous chemical sediments but also their diagenetic equivalents in sedimentary rocks (Do Nascimento et al. 2016). On the context of evaporites, the ones of sulphate composition are mainly formed by gypsum (CaSO4·2H2O). Gypsum is a saline mineral, monoclinic, commonly prismatic, white in colour and streak if pure, o
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