HUANGLUNGQI SEDIMENTARY FACIES IN THE YANGTZE REGION

The Upper Carboniferous Huanglung Formation in the eastern Sichuan may be divided into three members, which can be correlated with the previously established three fusulinid zones-Pseudostaffella,profusulinella, and Fusulinella- Fusulina-of the Upper Carboniferous Weining Formation in westGuizhou.In this paper on the base of correlation with equivalents in Yangtze region, sedimentary facies are divided chronologically.It is thought that the Huanglongqi transgression began from south to north and during Ijthe stage it obviously came from the north.During the early and middle stages the yangtze Sea is substantically a narrow-elongated gulf in an east-west direction, with ""Daba Mountain-North Hubei old land and Huaiyang old land in the north, Upper Yangtze old land in the west and southwest, low plain Jiangnan old land in the south, and Cathaysian old land in the southeast. Upper Yangtze old land and Jiangnan old land are joined by slight saddle at Jingjiang.The gulf is topographically higher in the west and lower in the east and its lower tidal line lies roughly between Tongling and Chao Xian in southern Anhui.The sea water flew into the middle Yangtre gulf in a form of tide or through the Jingjiang tidal mouth and then westward into the Upper Yangtze gulf. The sea water of Upper Yangtre gulf arrived only during special storm. That: is why the tidal flat sediments are extraordinaryly widely distributed during the early and middle stages.Thus it is explained that how sea water far from a thousand kilometer entered and retreated the tidal flood area of Yangtze gulf.During the late stage when the Jiangnan old land subsided, the sea water transgressed from both south and north, expanding the limited sea to a normal shallow sea, where the sediments were simple in nature but great in thickness with organisms rather flourishing.Each stage lacked oil- producing enviroments and coarse clastic sediments formed in high energy enviroment. For lack of high porosity sedimentary facies, primary reservoir conditions are not good.In the middle and upper Yangtze region parasyngenetic dolomites were developed in the intertidal zone during the early and middle stages, which is easy to be dissolved by fresh water and favorable for the formation of reservoir space for oil and gas. The gas produced in East Sichuan derived essentially from them On the edge of Jiangnan old land in lower Yangtre area and its northeast extended zone, although there txsisls dolomite facies favorable for reservoir of oil and gas, concidering the other factors, the testervoir condition is reia tively poor.