Biological marker indicators of paleo-depositional environment for the Eocene formations around Zara-Bolucan region (central anatolia, Turkey)

[摘要] 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 (GC) and gas chromatography-mass spectrometry (GC-MS) 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 T m /T s , C 29 T s /C 29 hopane ratios.

[关键词] Sivas Basin;organic geochemistry;biomarkers;Zara;Eocene;paleo-environment