Microscopic fabrics and microbial lithogeneous processes of Mesoproterozoic carbonate rocks in the Ordos basin

Abundant stromatolite, thrombolite and oolite can be found in Mesoproterozoic Jixian System in the Ordos basin, in which significant biogenic fabrics were observed by means of electronic microscope, scanning electron microscope and cathodoluminescence. The laminas of the stromatolite is the product of the interaction between the intermittent microbial activities involving both mechanical trapping and biologically-induced mineralization and normal carbonate sedimentation in certain sedimentary settings. The clotted texture of the thrombolite probably took shape during the shrinkage and rupture of the degraded extracellular polymeric substance (EPS) with many carbonate masses in three-dimensional space. The development of the ooids' spheres is similar to that of the laminas in the stromatolite. Ooids with and without dark cores are all biogenic in nature possibly related to solid biomicrospheres and hollow photosynthetic O2 bubbles encased by calcium carbonate respectively. The unique microscopic fabrics indicate the formation of different kinds of carbonate rocks in the study area is the combination of biological and abiotic processes closely related to microbial activities involving specific biophysical and biochemical mechanisms under favorable paleoclimatic, paleoceanographic and paleotectonic conditions in Mesoproterozoic Era. The diversity of the microbial carbonate rocks is due to different habits of the microbes in certain sedimentary settings with corresponding water energy. © 2022, Science Press. All right reserved.