Biological marker indicators of paleo-depositional environment for the eocene formations around zara-bolucan region (Central anatolia, turkey)

Abstract

Biological marker (biomarker) characteristics and paleo-depositional conditions of Eocene sediments around Zara-Bolucan northeast of Sivas Basin have been determined by means of detail organic geochemical studies such as gas chromatography and gas chromatographymass spectrometry analysis. In the investigated area, northeast section of the Sivas Basin, the Eocene Bozbel and Kozluca Formations consist of a organic matter rich sedimentary rocks deposited within trangressive-regressive cycles. During the evaluation of paleoenvironment characteristics with biomarker data, data related to n-alkanes, isoprenoids, terpenoids and steroids were used. Especially, the marine environment features indicated by C23 tricyclic/C30 hopane, the C26 /C25 tricyclic terpanes, homohopane/C30 hopane and diasterane/regular sterane data. The ratios of Pr/Ph, Pr/n-C17 and Ph/n-C18 indicate that there is marine organic matter predominantly precipitated under reducing environmental conditions. In the studied samples, the algal-bacterial organic matter contribution was interpreted to be due to the superiority of the C23 tricyclic terpene to C24, as well as larger than the C24 tricyclic terpane. However, the gammacerane index suggests that there is initially a low salinity environment. The significant terrestrial organic matter contribution is indicated by the isoprenoid and biomarker ratios, dominance of higher n-alkanes such as n-C29, n-C31, CPI, TAR values, n-C19 /n-C31, relative abundance of C27-C28-C29 regular steranes. Suboxic to anoxic palo-depositional conditions are confired by the isoprenoid and n-alkane ratios and Tm/Ts, C29Ts /C29 hopane ratios.