上奥陶统五峰组海底麻坑沉积的首次识别及其地质意义OA北大核心CSTPCD

Seafloor pockmarks are commonly seen in various marine environments.The study on the pockmark sediments,however,have been hardly involved in the literature,causing few knowledges of their characteristics,origin and identification.In this study,we recognized the pockmark sediments from the Paleozoic fine-grained rocks for the first time in China.Based on the field observations and sampling of Upper Ordovician Wufeng Formation at Ganziping and Xiebutou in Shizhu,Chongqing,we tested pock-mark rocks with microscope,scanning electron microscope(SEM),and major and trace element analy-ses.We found the bed chaos and arched beds in the lentoid or cuneal pockmark sediment body.Breccia carved by siliceous veins,are commonly seen,together with asphalt and barite,hematite minerals in the pockmark sediments.Observations and results of major element and REE suggest that the formation of pockmarks were unrelated with hydrothermal liquid and cold seeps.All the geological facts indicate the low-matured oil and gas generated from the Wufeng Formation as the first essential for the formation of pockmarks.The identification marks of deep-time pockmarks are thought as:(i)negative relief in seismic sections,(ii)lentoid or cuneal sediment body,(iii)chaos beds,(iv)arched beds,and(v)hiatus and temporal chaos of sediments.Meanwhile,petrological,stratigraphical,paleoenvironmental and petro-geological significances of the pockmarks in the Wufeng Formation are discussed in this study.