Sedimentary Facies And Hybrid Sedimentation Characteristics Of The Lower-Middle Cambrian Mantou Formation In Yuntaishan World Geopark

The Yuntaishan World Geopark is located in the southern edge of the North China Plate. The Lower Paleozoic which constitutes the main landform of the park is well exposed, and the Mantou Formation of which, with complex lithologies developed in diverse environments, perfectly records the Early-Middle Cambrian transgression process. Studies on the characteristics of the hybrid sedimentation as well as the types of the sedimentary facies will substantially contribute to the reconstruction of sedimentary environments and help to delineate the sea level fluctuations in the aforementioned time interval in the study area.The sedimentary facies and microfacies, especially the hybrid sedimentary facies of the Lower to Middle Cambrian Mantou Formation are extensively discussed in the present study. The Mantou Formation reveals a hybrid carbonate platform as a whole, two subfacies i.e. hybrid tidalflat and hybrid limited platform and ten microfacies i.e. supratidal mudflat, mixed intertidal flat, hybrid intertidal flat; hybrid lagoon, oolitic beach, hybrid oolitic beach, shoal, hybrid shoal, hybrid tidal channel, and hybrid intershoal sea microfacies have been figured out. Hybrid sequences are well developed herein, and three categories of hybrid sedimentation have been recognised,i.e. gradient hybrid sedimentation, mutant hybrid sedimentation, and composite hybrid sedimentation type I.Researches on microfacies and hybrid sedimentary types have revealed that the main control factors on the hybrid sedimentation are sea level changes and sediment supply. The sea levels fluctuate but rise up as a whole in this period while the speeds of the sea level changes are alternatively fast and slow. The speed is lower during the formation of the lower member of the Mantou Formation, and higher while the middle member and the lower part of the upper member form, and lower again as the rest of the upper member deposits.