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ORIGINAL RESEARCH article
Front. Earth Sci.
Sec. Sedimentology, Stratigraphy and Diagenesis
Volume 13 - 2025 | doi: 10.3389/feart.2025.1497600
This article is part of the Research Topic Advancements in Carbonate Geology: Depositional settings, Sedimentology, Chemostratigraphy, Reservoir Characterization, and Environmental Sustainability View all 5 articles
Characteristics and the genesis formation mechanism of the dolomite reservoirs from Ma5 6 -Ma5 10 sub-member of thefor lower Lower Ordovician Majiagou Formation, Wu Qi area in central Ordos Basin, China
Provisionally accepted- 1 Shaanxi Yanchang Petroleum Group Co.,Ltd, Xi'an, China
- 2 PetroChina Changqing Oilfield Company, Xi'an, Shaanxi Province, China
The distribution of anhydrite contributes to the formation of high-quality dolomite reservoirs. However, the lower part of the Lower Ordovician Majiagou Formation in the central Ordos Basin shows significant natural gas potential despite in anhydrite-depleted settings. Therefore, its formation mechanisms is crucial for carbonate hydrocarbon exploration in evaporite-depleted regions globally. Through integrated multidisciplinary analysis (petrography, cathodoluminescence (CL), X-ray diffraction (XRD) and carbon (C)-oxygen (O)-strontium (Sr) isotopes), this study reveals the sedimentological-diagenetic differentiation mechanisms of two dolomite types: (Very) finely dolomite (Md1) features micritic or microcrystalline (<20μm), euhedral to subhedral dolomite crystals with laminated structure observed, the CL shows a very dull or dark red in color, and low order degree (0.65 on average), indicated that Md1 formed in a restricted platform tidal flat environment with weak hydrodynamic conditions. Fine-medium crystalline dolomite (Md2) is composed by finely or medium crystalline (20-60μm), euhedral to subhedral dolomite crystals, the dark red or orange in color by CL analysis, and high order degree (0.85 on average), indicated that Md2 formed in the tidal flat shoal environment under weak hydrodynamic conditions. The C-O-Sr experiment results showed the Md1 exhibits a positive δ13C shift (+0.83‰ on average), high paleosalinity Z value (125.9747 on average) and Sr isotope ratio (⁸⁷Sr/⁸⁶Sr = 0.70967 on average), indicated that Md1 formed during the syngenetic-quasi syngenetic stages through the reflux of high-salinity seawater in an open, low-oxidation, low-temperature environment. Md2 exhibits a negative δ¹⁸O shift (-7.12‰ on average), low paleosalinity Z value (122.8781 on average),and Sr isotope ratio (⁸⁷Sr/⁸⁶Sr = 0.70946 on average), indicated that Md2 formed through the superimposed transformation of the original tidal flat shoal during the shallow burial stage, driven by the reflux of reducing seawater in a closed, low-reduction, higher-temperature environment. In addition, the atmospheric freshwater dissolution and the enhanced euhedral growth of dolomite crystals during the burial stage promote the development of high-quality reservoirs. This study provides novel geochemical and sedimentary insights for predicting dolomite reservoirs in anhydrite-depleted settings, aiding global hydrocarbon exploration in similar basins.
Keywords: Dolomitization, diagenesis of dolomite reservoir, Majiagou Formation, Wuqi area, Ordos Basin
Received: 17 Sep 2024; Accepted: 25 Feb 2025.
Copyright: © 2025 Tian, Zhou, Yin, Xue, Cao and Ma. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Kun Tian, Shaanxi Yanchang Petroleum Group Co.,Ltd, Xi'an, China
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