SEDIMENTATION OF EXTENSIONAL BASINS IN PLATFORM REGIONS OF CHINA
Sun Shu Fan Delian Chen Haihong Wang Qingchen (Institute of Geology, Academia Sinica)
Extensional basins in platform regions of China can be divided into three types; intracontinental faulted basin and rift, aulacogen, and passive continental margin. Intra continental faulted basin and rift are predominated by nonmarine deposits, with some exceptions of marine transgression in paralic basins. During the processes of rifting, basalt-red bed-evaporite association or basalt-red bed-coal bearing series association→deep water lacustrine association→red bed association could be formed successively. Rock associations in medium to small faulted basins are similar but mostly incomplete, also with differences in volcanic rock types. The strike of depositional facies belt is controlled to some extent by characteristic tectoienic-morphologic configuration of faulted basin and rift. Differences of aulacogen from rift lies in: long period of development, connected with geosyncline at a high angle and marine environment dominated in whole evolution. In the Henan-Shaanxi Aulacogen, rock associations formed during the processes of basin development are in the sequence of lower siliciclastics association, volcanic rock (dominated by potassic basalt) association, upper siliciclastics-carbonate association, as well as relatively deep water facies mud silicalite, which is basically similar to other aulacogens. Deep water association should be further investigated, however. Distribution of sedimentary facies belt is also controlled to a certain extent by tectonic-morphologic configuration. Tidal dominated environment is quite similar to modern analogues The early Cambrian sea in the southern part of Yangtze Platform where once was a passive margin was a wave-dominated shelf environment, with little differences to modern analogues. Early Paleozoic stone coals developed in the southeastern margin of the Yangtze Platform and its adjacent area probably are pel agic and hemipelagic deposits. The anoxic event relatedto a warm ocean with high sea level possibly occurred during the Sinian and early Paleozoic. The formation and distribution of some mineral resources are also controlled by ext ensional basins, such as turbidite and burial hill oil reservoirs in the Tertiary rift, phosphorite and nickel-molybdenum polymetal ore deposits in shelf region of the passive continental margin. It is rare in the world that anoxic event of oceans had made stone coal widely distributed, stone coal should be considered as an important hydrocarbon source rock. Many reports have shown that some mineral resources are closely related to aulacogen, such as Precambrian syndeposi-tional layered and massive sulfide deposits and uranium-vanadium-copper stratabo-und deposits, even the Witwaterstrand type gold-uranium pyrite ore deposits in South Africa. Therefore, it is necessary to treat extensional basins including aulacogen with a due concern.