Early cretaceous limestones outcropping in Gümüşhane area (NE Türkiye) investigation of organic geochemical properties, depositional environment and conditions

In this study, the organic geochemical properties, depositional environment, and conditions of the Early Cretaceous aged platform carbonates outcropping in the Gümüşhane region were investigated. Within the scope of the study, it was determined that the thickness of the unit varies between 90 and 600 m and has 7 different lithological features, and the age range of the fossils in the limestones represents the Barriasian-Aptian (Early Cretaceous) period. It has been determined that the bituminous limestone samples belonging to Çukutbaşı ÖSK and SK5 drilling well have medium-suitable source rock potential, while the bituminous and micritic limestones belonging to other ÖSKs and SK4 drilling well do not have source rock potential. It has been determined that the samples belonging to Keçikaya and Çukutbaşı ÖSKs have moderate hydrocarbon generation potential and organic matter content that will produce Type II/III kerogen and gas/oil. It was determined that the samples from other ÖSKs and drilling wells had organic matter content that would produce Type III kerogen and gas/oil. According to the average % Ro, Tmax values of the samples, thermally immature-mature, according to the MA(I)/MA(I+II), TA(I)/TA(I+II), C29ββ/(ββ+αα) sterane, C2920S/(20S+20R) and (4MDBT/1MDBT) ratios, it has reached the early-medium mature level. Based on total sulfur (TS) values, Sr/Ba, V/Ni, Pr/Ph, n-C17/n-C27 ratios, TAR values, Pr/n-C17 and Ph/n-C18, C19/C23 TT, C24Tet/(C24Tet+C23TT), C21/C23TT, C26/C25TT C3122R/C30H, C35/C34 homohopane, C3122R/C30H, C35/C34 homohopane ratios, C29ααα20R>C27ααα20R>C28ααα20R sterane rank, parameters such as Log (1MP/9MP) and C29/C27 sterol ratios, and δ13C isotope values of the samples, it was determined that the examined rocks were deposited in the terrestrial-marine transition zone where oxic-suboxic and anoxic redox conditions prevail. It was observed that it was deposited in a failed rift environment where both terrestrial and marine organic matter input was possible, with terrestrial organic matter being more dominant. It has been determined that the sea level, which rises and falls from time to time during deposition, affects the amount of organic matter accumulation.