论古代海洋碳酸盐沉积环境基本模式

我国碳酸盐地层分布广泛,厚度巨大,类型复杂,从而为我国碳酸盐研究提供广阔前景。解放以后,我国首先在四川盆地的二、三叠系碳酸盐岩中获得高产气田,推动了碳酸盐岩的研究。

A BASIC MODEL OF THE ANCIENT MARINE ENVIRONMENT FOR SEDIMENTATION OF CARBONATE

The results of our preliminary studies on the Middle Devonian, Late Permian and Middle Triassic carbonate faeies from Guizhou province and the Early-Middle Triassic from Sichuan are given as follows.1. Faeies pattern of the Middle Devonian in Guizhou ProvinceThere the faeies pattern of the Middle Devonian was controlled by the Central-Guizhou landmass extending in an east-west direction. In the region from Guiyang to Longli, Duyun and Kaili, the deposits are represented by offshore terrigenous clastics composed of mainly quartzites with subordinate mudstones and dolomites. The Central-Guizhou landmass was intermittently uplifted during the Middle Devonian, supplying much terrigenous elastics to form the offshore deposits. A wide transgression took place perhaps by late Middle Devonian, when the carbonate deposits with prolific stenohaline fauna (corals and stromatoporoids) were developed.Further south in Huishui and Changshun districts, there developed a carbonate platform after the name of Huishui-Changshun. In this carbonate sequence are intercalated two layers of quartzite which show that the offshore terrigenous deposits derived from the central Guizhou landmass extended to the carbonate platform. Along the margin of this platform there is a series of reefs composed of corals and stromatoporoids. However, these organisms could not constitute a huge reef owing to the interference of terrigenous elastics.In this region from Ziyun and Luodian to Nandan, south of the carbonate platform, the Middle Devonian is represented by open marine basin deposits, consisting chiefly of grey and greyish black thin-bedded calcareous mudstones with some siliceous shale, marls and sandstones. Moreover, these deposits also contain abundant pelagic (planktonic and nektonic) fauna, such as Tentaculites, Hyolithes, Trilo-bites and ammonites.The carbonate platform extends further south in the Wangmo-Anlong area, judging from the general lithologic characters, despite the scarcity of outcrops and insufficient data.2. The Late Permian sedimentary faeies in East Yunnan-South GuizhouIn this region the Niushoushan landmass was gradually uplifted, supplying a large amount of terrigenous elastics during the Late Permian, and in the Weining and Shuicheng districts very thick coal-bearing terrigenous elastics were deposited presumably in terrestrial swamps or paralic swamps. Toward the south-east near Guan-ling there occur deposits that are transitional between terrestrial or paralic elastics to platform carbonate. Further south-eastward, in the Ziyun, Wangmo and Ceheng counties there appears again the carbonate platform, the margin of which is dotted with many reefs composed of calcareous algae, sponges and bryozoans and they may extend as barrier reefs.Further on in the same direction the carbonate platform deposits are replaced by carbonate shelf deposits composed mainly of cherty limestones and thin-bedded siliceous rocks.3. The sedimentary facies of the Middle Triassic in Guizhou ProvinceThe facies-change belt extends over the whole Guizhou in a nearly NE to SW direction. On both sides of this belt, the lithology and life assemblages differ greatly from one other. On the north-west side are predominantly carbonate rocks, while on the south-east elastics, and the differ remakably in thickness. Hence the northwestern part of this belt is called the carbonate platform of south-west Guizhou. Along its margin are a great number of reefs, e. g. the Qingyan and Nidang localities. On the south-east side of the belt exist open sea basin deposits of fine elastics with some limestones, siliceous rocks and turbidites as well, which contain pelagic ammonites and thin-shell bivalves (such as Halobia, Daonella and Posidonia).4. The sedimentary facies of the early stage of Early Triassic Feixianguan Formation, Sichuan ProvinceDuring the early stage of Early Triassic, the Feixianguan Formation was formed with two different types of deposits. To the west of Huayingshan and Qing-shanling mountains, it is represented by purplish terrigenous clastics, while around th