Abstract: A set of bioclastic limestone rich in glauconite was widely developed in the Ordovician Dawangou Formation in the northwestern margin of Tarim Basin. This paper aims to investigate the sedimentary dynamics characteristics of Dawangou Formation, and provide mineralogy support for palaeogeographic reconstruction and reservoir evaluation for the Ordovician of Tarim Basin. The petrological and geochemical characteristics of the glauconite were analyzed through thin-section identification under microscopy, scan electron microscopy (SEM), energy dispersive spectroscopy (EDS), major, trace and rare earth element analysis, in order to reconstruct the sedimentary environment of the Ordovician Dawangou Formation in the northwestern margin of Tarim Basin. The results showed that glauconite in this area was of granular verdissement origin, with bioclasts and carbonate particles serving as the parent material. It was classified as para-autochthonous glauconite. The glauconite in Dawangou Formation appeared emerald to dark green, with granular or cluster-like structures. The K₂O content indicated a mature to highly mature stage. The average values of Al₂O₃/(Al₂O₃+Fe₂O₃) and La_N/Ce_N represented a continental margin depositional environment. The average values of Th/U, Ni/Co, Ⅴ/Sc, and Ⅴ/(Ⅴ+Ni) further confirmed that the Ordovician Dawangou Formation in the northwestern margin of Tarim Basin was in asuboxic- weak reduction environment. Integrated with the regional geological background, it was concluded that the Ordovician Dawangou Formation in the northwestern margin of Tarim Basin primarily was developed in shallow marine shelf facies. The study of the glauconite in Dawangou Formation could provide mineralogy evidence for reconstructing the paleoenvironment in the Ordovician.