Carbonatite Microfacies Analysis And Vertical Evolution Characteristics Of The Taiyuan Formation, Western Henan Province

Based on the detail measurement and description of the Lower Permian TaiyuanFormation exposed in Jiaozuo and Yuzhou areas in the western Henan Province, thispaper mainly observed crystal structure, particles types and microfacies characteristicsin the each layer of carbonatite by using polarized light microscope, and4types ofcrystal structure of carbonatite were found in this Formation, including micrite, finepowder crystal, coarse powder crystal and very fine crystal. Bioclasts are the chiefparticle types in the carbonatites. According to the characteristics of grain size, particlestype and their abundance, biological assemblages and their paleoecology,15kinds ofcarbonatite microfacies may be recognized, i.e., fine powder crystal bioclastic limestonecontained ostracoda (Microfacies-1, or MF-1for short), coarse powder crystal limestonecontained bioclasts and algae (MF-2), coarse powder crystal limestone containedbioclasts (MF-3), fine powder crystal bioclastic limestone (MF-4), fine powder crystallimestone contained bioclasts (MF-5), powder crystal limestone (MF-6), very finecrystal limestone contained bioclasts (MF-7), coarse powder crystal bioclastic limestonecontained echinodermata and foraminiferans (MF-8), coarse powder crystal limestonecontained foraminiferans and echinodermata (MF-9), fine powder crystal bioclasticlimestone contained foraminiferans (MF-10), fine powder crystal limestone containedbrachiopoda (MF-11), bioclastic micrite contained brachiopoda (MF-12), fine powdercrystal bioclastic limestone contained echinodermata (MF-13), bioclastic micritecontained echinodermata (MF-14) and micrite contained bioclasts (MF-15).Through the comprehensive analysis of depositional features, trace fossils and thecomposition characteristics of biodetritus in different microfacies, the15types ofmicrofacies were explained to form in four facies belts, namely the bay-lagoon(MF-1and MF-2), restricted platform (MF-3, MF-4, MF-5and MF-6), shoal in theplatform (MF-7) and open platform (MF-8, MF-9, MF-10, MF-11, MF-12, MF-13,MF-14and MF-15). Thus the sedimentary environment model of the carbonatitemicrofacies types in the Taiyuan Formation was put foward. On this basis, combinedwith the distribution of the trace fossils, the paper analyzed the vertical evolutioncharacteristics of the carbonatite microfacies and trace fossils of the Taiyuan Formation in Jiaozuo and Yuzhou area, and revealed that the study area underwent twicelarge-scale transgression in the Early Permian.