Sedimentary characteristics of the Sinian Dengying Formation in Pengshui,Chongqing

The petrographic and sedimentological characteristics of the dolostones from the Sinian Dengying Formation in Pengshui,Chongqing are explored on the basis of the Dengying Formation section in the coral part of the Laochangping anticline.These dolostones may be divided,from the base upwards,into two parts: "algae-rich" and "silica-rich" intervals.The sedimentary environments consist of the tidal-flat to restricted platform subfacies,including the lagoon,subtidal,intertidal and supratidal microfacies.The sedimentary model has been constructed for the Sinian Dengying Formation in the upper Yangtze area.Vertically,the Dengying Formation once went through two phases of sea-level changes dominated by regression and displays the shallowing-upward depositional sequences.Horizontally,the sedimentary environments passed,from NW to SE,into the tidal flat-lagoon through restricted platform to the open platform,and finally to the platform margin and continental shelf.