Characteristics and genesis analysis of middle and lower Ordovician dolomite in the southern margin of the Ordos Basin, China

Abstract

The Middle-Lower Ordovician formations in the southern margin of the Ordos Basin host multiple sets of dolomites, which readily form high-quality reservoirs with promising exploration prospects. Understanding the geochemical characteristics and analyzing the genesis of these dolomites in this region is crucial. Based on drilling, logging, core observation, and thin section identification, representative dolomite samples from the Xiweikou, Jueshangou, and Caojiagou profiles were selected for comprehensive geochemical analysis. Combined with the petrological characteristics and cathodoluminescence features of the dolomites, their characteristics and genesis were analyzed. The results indicate that the average 87Sr/86Sr ratio of 11 dolomite samples in this area is 0.710842. The rare earth element distribution pattern shows an enrichment of light rare earth elements (LREE) and a depletion of heavy rare earth elements (HREE). The micritic and finely crystalline dolomite crystals are euhedral to subhedral, with low ordering, high Na, K, Sr, and low Fe, Mn content. Under cathodoluminescence, they emit rose-red to dark-red light, indicating a product of penecontemporaneous dolomitization. The sandy crystalline dolomites (fine, medium, and coarse crystalline) generally have anhedral to subhedral crystal forms, high ordering, low Na, K, Sr, and high Fe, Mn content. Under cathodoluminescence, they emit dark-red or no light, indicating a product of burial diagenesis.

Keywords

Ordos basin / Ordovician system / Geochemical analysis / Dolomite characteristics / Dolomite genesis

CRediT authorship contribution statement

Xinyi Tang: Formal analysis, Investigation, Methodology, Writing-original draft, Writing-review & editing. Zijing Li: Supervision, Methodology. Hong Fang: Resources, Data curation. Yang Li: Writing-review & editing, Writing-original draft, Software, Resources, Methodology, Investigation, Formal analysis. Zongyang Dai: Supervision, Resources, Methodology, Investigation. Tian Li: Investigation. Peng Lai: Formal analysis, Data curation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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