PETROGENESIS AND SEDIMENTARY ENVIRONMENT OF THE PERMIAN CHERTS IN THE YANGTZE REGION

The studies on Permian cherts from the two typical sections(Shangsi section of Guangyuan area and Nashui section of Luodian area) in the Yangtze region indicate that distict REE characteristics occur among banded,nubby and lamellated cherts in different areas.The ∑REE values in banded and nubby cherts are less than that in lamellated chert.There are semblable Ce/Ce^* values in cherts of different occurrences in same area,but it is quite different in these two areas.In this paper,through comparison and analysis of cherts and surrounding rocks(including limestone and shale),of them,the ∑REE values in shales are the highest,and the next is the lamellated cherts,then the limestone,but the lowest is banded chert.The studies on petrological characteristics and REE geochemical characteristics in cherts show that the Permian cherts in the Guangyuan area are mainly biological sedimentation,but are effected by hydrothermal sedimentation,and they are formed in the middle-lower part of continental shelf.While the Permian cherts in the Luodian area are mainly hydrothermal sedimentation,and the non-hydrothermal sedimentation is also interfused.They are formed in oceanic basin.