Organic Petrology of the CambriarrSinian Chert from the Xiangchuan Region

Key words: 
• chert /
• orgyic petrology /
• formation environment /
• Xiangchuan region

Abstract: The Xiangchuan regionis referred to Shoushan County，Sichuan Province and the western and middle parts of Hunan Province where Sinian-Cambrian bedded cher is are w ell-dev eloped. T he orgyic car-bon content in the chert samples is relatively high, ranging from 0. 06 to 9. 00% and averaging 1. 91%.The linear positive relationship between organic carbon concentrations and some trace element contentsis not clear. Microscopic studies of the kerogen from the chert samples show that the main componentsprobably take place; and 3) that the chert is formed in a shallow continertal-margin stagnant basin.results sug-gent that the primary mother materials basically belong to Type一I amorphous kerogen. On the Van Krevelen diagram，all samples fall into the metagenesis field. Stable carbon isotopes of kerogen from the chert samples range from一29. 30 t0，一3 5. 84%.Analysis of thefeatures of organic petrology mentionedabove suggests 1)that organisms and their degraded products contribute much to the formation of chert, 2) that in the formation of the chert a scalled elimination of impurity matters”processes may