Abstract: Molar-tooth structures (MTS) and storm deposits were widely developed in the carbonate sedimentary system of shelf-ramp-platform margin from the Jiayuan Formation to the Zhaowei Formation of Neoproterozoic in Xuzhou area. Based on field observations of outcrops and indoor comprehensive analysis, MTS were divided into autochthonous MTS containing banded M1 (straight banded M1-a; branched banded M1-b), worm-like M2 (short wormlike M2-a; long wormlike M2-b), filiform M3, suspension needle-like M4, and allochthonous MTS containing clastic M5. The five types mainly occur in the area from the lower area of gentle ramp to the tidal flat. Based on the background of seven typical storm sequences of different water depths and hydrodynamic conditions, correlation analysis was performed between morphology, distribution of the MTS, and the instantaneous high-energy event deposits. The analysis shows that close correlation was found between MTS and the storm events, indicating that M3 is mainly present in the massive layers in fine weather. The M1 and M2 were mainly formed in turbulent environment during fluctuating period with frequent earthquakes and storms. While the M4 and M5 are the principal types in the layers formed during the storm upsurge period, the strength of the storm andthe water depth control the scale of the storm sequence, and further control the morphology and distribution of the MTS. Therefore, during the different stages of the storm cycle, the form of MTS includes two interrelated processes: crack formation and microspar filling under the special marine and atmospheric paleoenvironment during the Middle-late Proterozoic. During the early period and the climax period of a storm, the storm wave has influenced mainly on the crack opening stage of the MTS formation; while the storm waves mainly influence the filling stage during the later period. Finally, Molar-tooth structure-bearing carbonate, a special type of an event carbonate in the geological history, was formed and widely distributed.

Key words: Neoproterozoic, Molar-tooth Structure (MTS), earthquake, storm deposit