扬子区石炭纪黄龙期沉积相

扬子区石炭纪黄龙期海侵主要由南而北,晚时海水北来明显。早、中时扬子海实为一东西向狭长形海湾,地形西高东低,低潮线约在皖南铜陵、巢县向;海水除由下扬子湾可随潮而溯流入中扬子湾外,并可由荆江潮口随潮而进入中扬子湾,再西而入上扬子湾,此即早、中时潮坪沉积分布特宽的原因。晚时江南古陆下沉,南北海水大侵,使海侵达到高潮,改早、中时局限海为正常浅海沉积,岩性单一,生物繁茂,厚度较大。早、中时中、上扬子区潮间带准同生白云岩发育,易为后期淡水溶蚀而多孔,是有利于油气储集的沉积相。

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.