Sedimentary environments and genesis of the molar-tooth structures in the Neoproterozoic Jiayuan Formation in the Xuzhou region, Jiangsu

The molar-tooth structures, a special kind of sedimentary structures with special textures and restricted time duration only developed in the Meso-to Neoproterozoic carbonate rocks are observed in the storm deposits from the Neoproterozoic Jiayuan Formation in the Xuzhou region, Jiangsu. The morphology, sedimentary environment and genesis of molar-tooth structures are treated in this study in terms of field observation and laboratory study. The molar-tooth structures in the Jiayuan Formation appear in the ramp zones of the subtidal carbonate rocks at the latitudes of 20°N to 34°N. The distal storm currents penetrated into the fissure systems produced by the earthquakes on the ancient marine basement, led to the chemical reactions with the pore-space water, and finally led to the rapid crystallization of calcite. The physical and chemical conditions of the Proterozoic oceans and atmospheres and tectonic settings are interpreted as the main factors controlling the spatio-temperal distribution of the molar-tooth structures.