The origins and sedimentary environment of glauconite in Ordovician Dawangou Formation, NW Tarim Basin, China

Abstract

A bioclastic limestone containing a high concentration of glauconite is extensively present in the Ordovician Dawangou Formation at the NW Tarim Basin, China. This study investigates the petrology and geochemical properties of glauconite through microscopic thin section analysis, scanning electron microscopy, and major and trace element analysis. The genesis, maturity, and sedimentary environment of the glauconite are discussed. The results indicate that the glauconite in this region originates from granular glauconitization, derived from bioclasts and carbonate particles, forming quasi-autochthonous glauconite in a weak oxidation-weak reduction environment. The glauconite in the Dawangou Formation exhibits emerald green to dark green coloration, granular or flower-like structure, with a K₂O content ranging from 6.27–8.73% and an average of 7.19%, indicating maturity to high maturity. The values of Al₂O₃/(Al₂O₃ + Fe₂O₃) and La_N/Ce_N average 0.78 and 0.81, respectively, suggesting a continental margin sedimentary environment. The average values of Th/U, Ni/Co, and V/Sc are 2.74, 10.54, and 0.16, respectively, confirming the weak oxidation-reduction conditions of the Ordovician Dawangou Formation. Considering the regional geological context, it is inferred that the Ordovician Dawangou Formation in NW Tarim primarily represents slope-basin facies. This study of glauconite in the Dawangou Formation not only offers insights into the stratigraphic and sedimentary characteristics of the area but also serves as a valuable reference for further research in related fields.