Sedimentary Characteristics of Tidal Storm Deposit of Early Cambrian Qingxudong Formation in the Zhenyuan Area, Eastern Guizhou and Its Palaeogeographical Implications

Key words: 
• storm deposit /
• tidal flat /
• Cambrian /
• Qingxudong Formation /
• eastern Guizhou /
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Abstract: Storm deposits with typical features of were found in the Qingxudong Formation, Lower Cambrian（corresponding to Series 2 of Cambrian）in Zhenyuan area, eastern Guizhou Province. Based on field observation on the Jinpen Section and Liushaguan Section and laboratory analysis, sedimentary structures of storm deposit, such as erosion surface, coarse lag deposits, graded bedding, ripple beddings and rhythmic  lamination, are present  in the succession, excluding hummocky crossstratification. Particularly, the lagsuspension deposit couple is evident, winnowed coarse lag deposits occur in the below with an overlying fine laminated bed. Three types of storm deposit sequences with different vertical stacking patterns were identified. Sequence Ⅰconsists  of the coarse lag deposits, ripple beddings and rhythmic lamination upwards. The coarse lag deposits which are composed of gravels, intraclasts and ooids are the predominant parts. Sequence Ⅱconsists of the graded bedding and ripple beddings, and including wavy erosion surface in the bottom. Sequence Ⅲ is responsible for multistage small scale storm, including lag deposits and ripple beddings. The background deposit is gray laminated limestone, with ripple bedding, bird's eye structure, indicating tidal flat environment. In summary, the storm deposits in Zhenyuan is attributed  to tidal flat storm deposit, that enrich the style of storm deposits of Qingxudong Formation, early Cambrian, in eastern Guizhou and western Hunan. The distribution pattern of storm deposit of Qingxudong Formation, in eastern Guizhou and western Hunan was preliminarily summarized based on the previous work and this study. The discovery of storm deposits reflects indirectly the study area should be located in the low latitudes near the equator during the Early Cambrian.