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SOURCE ROCK POTENTIAL AND ORGANIC GEOCHEMISTRY OF CENOMANIAN‐TURONIAN BLACK SHALES, WESTERN TAURUS, SW TURKEY
Author(s) -
KaraGülbay R.,
Yurtsever T. S.,
Korkmaz S.,
Demirel I. H.
Publication year - 2010
Publication title -
journal of petroleum geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 42
eISSN - 1747-5457
pISSN - 0141-6421
DOI - 10.1111/j.1747-5457.2010.00484.x
Subject(s) - kerogen , cenomanian , geology , oil shale , source rock , total organic carbon , maceral , organic matter , vitrinite , pyrolysis , sedimentary depositional environment , maturity (psychological) , organic geochemistry , geochemistry , mineralogy , terrigenous sediment , hydrocarbon , environmental chemistry , sedimentary rock , chemistry , cretaceous , paleontology , petrography , organic chemistry , psychology , developmental psychology , structural basin
The depositional environment and hydrocarbon source rock potential of Cenomanian‐Turonian black shales of the Dereköy and Ballik Formations in SW Turkey were investigated by organic geochemical methods. In detail, 33 samples from three section of the Dereköy Formation, and 15 samples from one section of the Ballik Formation were analysed for elemental (TOC, Rock ‐Eval pyrolysis), C 15+ ‐lipid and biomarker compositions. Based on maximum pyrolysis degradation temperatures of not more than 420°C, all the shale samples are classified as immature, corresponding to a vitrinite reflectance of less than 0.45% R r and a lignite to sub‐bituminous coal stage. This is confirmed by relatively high isoprenoid to n‐alkane ratios as well as by high biomarker contents. According to this maturity stage, and both total organic carbon contents of 6–41% and hydrogen indices of 255–708 mg HC/g TOC, the Cenomanian‐Turonian black shales exhibit fair to excellent source rock potential with mixed Type II and Type I kerogen. Relatively high isoprenoid to n‐alkane ratios may indicate at least partial (bio‐) degradation/evaporation/waterwashing and selective modification of the lipid composition due to the nature of the outcrop. However, very similar unimodal n‐alkane distributions in the gas chromatograms of four selected shale samples, with a predominance in the C 16 to C 17 region, clearly point to a significant contribution of algal and/or bacterial type organic matter with low terrigenous organic input. C 27 , C 28 and C 29 steranes in shales from both formations have similar distributions (C 29 >C 27 >C 28 ). High C 31 R homohopane / C 30 hopane ratios indicate a marine depositional environment. This is confirmed by the presence of gammacerane in all the black shales investigated which in general indicates salinity. Pregnanes in one sample (BA‐6) may point to hypersaline conditions.