The Biomarkers And Their Significance From The Microbialite Of The Mantou Formation In Cambrian, Mianchi Area, Western Henan

The Mantou Formation of Cambrian superbly and continuously exposed in Mianchi Area, western Henan. The paper anylyzes the macro and micro features of stromatolites, oncolites, thrombolites and bioclastic limestones, and detects the compositions of biomarker compounds by GC-MS. Baesd on thses results, the characteristics of composition and distribution of biomarker compounds and the sedimentary environments are discussed.Abundant organic matters including n-alkanes, branched paraffin, isoprenoid and some fatty alcohol were detected by GC-MS in the stromatolite, oncolite and thrombolite of the Mantou Formation in Cambrian, Mianchi Area. The carbon number distribution of n-alkanes was nC12-nC35 in the oncolite and thrombolites, while in stromatolites the number was nC14-nC35. In the three types of microbialites, abundant methyl branched alkanes, which are short- and middle-chain or high carbon number, were detected, such as 7-methyl hexadecane and 10-methyl eicosane. Among the isoprenoid detected, Pristine(Pr) and Phytane(Ph) was the most abundant. Furthermore, the values of Ph/C18 and Pr/C17 were larger than one. Together these results, it is suggested that the main sources of bio-input of stromatolites, oncolites and thrombolites were the bacteria and the algae. It is well consistent with the microbiogenic mechasism of microbialite. However, the ratio of light dydrocarbon(Carbon number <21) in thrombolite was higher than that of stromatolites and oncolites. Because of light dydrocarbon resulting from the bacteria and the algae, so we considered that the microbiogenic mechasism is much more important in thrombolites than stromatolites and oncolites. In stromatolite and thrombolite, the values of Pr/Ph were less than one, and had the significant preponderance of phytane. The result suggests that their sedimentary environments are weak oxidation and reduction. Unlike stromatolite and thrombolite, the value of Pr/Ph was between 1.05 and 1.13 in oncolite, closing to one. It did not possess the significant preponderance of phytane, suggesting the sedimentary environment of weak oxidation and weak reduction.In bioclastic limestones, the carbon number distribution of n-alkanes was nC12-nC35, and the main carbons were C17 and C25. It is suggested that the main sources of bio-input contained at least the bacteria and the algae. The value of CPI was 0.99, suggesting the higher maturing degree. The value of Pr/Ph was less than one, and had the significant preponderance of phytane. The result suggests that the sedimentary environment were weak oxidation and reduction. The values of Ph/C18 and Pr/C17 were less than one. Moreover, abundant n-fatty acid methylesters were detected, and the carbon number was C13-C21. The variation of carbon number between n-alkanes and n-fatty acid methylesters was not consistent, suggesting they were derived from different parent material. These abundant n-fatty acid methylesters detected in bioclastic limestones indicate the weak reduction and neutral chemical environment. However, the other significances of geology need to be discussed in future.