Integrated isotopic and organic geochemical constraints on the depositional controls and source rock quality of the Neog
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ORIGINAL PAPER
Integrated isotopic and organic geochemical constraints on the depositional controls and source rock quality of the Neogene Kalamaki sedimentary successions (Zakynthos Island, Ionian Sea) George Kontakiotis1 · Vasileios Karakitsios1 · Angelos G. Maravelis2 · Stergios D. Zarkogiannis1 · Konstantina Agiadi1 · Assimina Antonarakou1 · Nikolaos Pasadakis3 · Avraam Zelilidis4 Received: 7 August 2020 / Revised: 2 November 2020 / Accepted: 4 November 2020 © Springer Nature Switzerland AG 2020
Abstract This study investigates the oxygen and carbon (δ18O, δ13C) stable isotope ratios, as well as the organic geochemical features of the 146-m-thick composite Kalamaki section located in the southwest margin of the Hellenic Fold and Thrust Belt (Zakynthos Island). The section includes Late Miocene–Pliocene pre-evaporitic, evaporitic, and post-evaporitic deposits. The obtained bulk geochemical data (Rock–Eval II, bitumen extraction, and fractionation) and biomarker compositions indicate poor–fair source-rock potential predominantly promising for gas production. TOC values indicate the presence of samples that might be of slight interest (0.50–0.95%) in the evaporitic interval and samples that are worthy of further investigation (up to 1.31%) in the pre-evaporitic sequence. The organic matter type (type III kerogen), along with the presence of plant remains (leaves) in the studied deposits reflect the mainly terrestrial origin of the organic material. Tmax and Production Index values further indicate that most of the sediments (138 out of 195 samples) are immature for oil generation and were not under high temperature conditions during burial, whereas 29 of them correspond to the mature oil stage. Oil generation requires deeper burial, which may have occurred offshore in the Ionian Sea. A marine paleoenvironment is indicated that received organic material from both marine and terrigenous sources. Isotopic values imply influence of continental fresh-water inputs in a high salinity, evaporative depositional setting. Furthermore, our findings provide evidence that the climate has favored the development of these source rocks by triggering relative sea-level fall, which in turn enhanced the preservation of organic matter by increasing sea-water salinity and suppressing carbonate deposition. Keywords Stable isotopes · Organic geochemistry · Source-rock potential · Hydrocarbon exploration · Paleoenvironmental reconstruction · Messinian Salinity Crisis (MSC) · Eastern Mediterranean
1 Introduction The recent discoveries have revealed the eastern Mediterranean as an important hydrocarbon province with significant petroleum systems (Belopolsky et al. 2012; Zelilidis and Maravelis 2015; Roveri et al. 2016; Ratner 2016; Grohmann et al. 2020). The distribution of hydrocarbons in the Mediterranean is mainly controlled by thick evaporites deposited Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42990-020-00045-2) contains supplementary material, which is available to authori
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