Distribution of Biomicrofacies and Cement Types in the Changxing Formation (Upper Permian), Western Hubei-eastern Sichuan Provinces, South China

The Changxing formation is subdivided into lower, middle and upper parts. Four types of microfacies were recognized in the Changxing formation. They include SMF-3, SMF-6, SMF-7 and SMF-19. The Changxing Formation is composed of deep basin margin, platform margin and open restricted platform environments. The lower, middle and upper parts are dominated by deep basin margin facies, platform margin facies and open restricted platform facies, respectively. The lower part contains foraminifera, radiolarian and mollusk organisms. The middle part is characterized by presence of crinoids, sponge, rugose, ostracods, trilobite, brachiopods, abundant bryozoans, mollusks and foraminifera organisms. The upper part is marked by dolomite, pyrite and abundant mollusks. Most of these organisms were concentrated within the middle part. The types of cements in the Changxing Formation consist of coarse grain sparite, micrite, microspar, silica and radiaxial cements. The lower part is dominated by silica cement. The middle part shows presence of abundant coarse grain sparite, micrite, microspar and radiaxial cements. The upper part is dominated by micrite, microspar cements.