Source rock potential and depositional environment of the Lower Oligocene İhsaniye Formation in NW Turkey (Thrace, Karaburun)

Abstract

The Lower Oligocene succession of the İhsaniye Formation, exposed at Karaburun on the Turkish (Thrace) coast of the BlackSea, provides insights into potential hydrocarbon source rock extent in the southwestern part of the Black Sea Basin. Presently, nodetailed study of the İhsaniye Formation exists with regards to organic matter content and type. We analyzed 78 fine-grained samplesfrom a c. 70-m-thick section near Karaburun. Relatively high total organic carbon (TOC) contents (average 1.45 wt.%) are present inthe lower part of the İhsaniye Formation; the hydrogen index values reach a maximum of 252 mg HC/g TOC, indicating the presence oftype III–II kerogen, and the organic matter is thermally immature (Tmax 418 °C). The presence of foraminifera and TOC/S ratios below2.8 confirm a fully marine environment. Elevated TOC contents and very low pristane/phytane ratios indicate an oxygen-depletedenvironment during deposition of the lower part of the İhsaniye Formation. The quartz/clay minerals ratio suggests a deepening trend inthe lower part of the succession and a shallowing trend in the upper part. Peculiarly, the low salinity “Solenovian Event” (in nannofossilzone NP23) is not developed although Sr isotope ratios indicate that the basin was only connected to the Mediterranean for shortperiods during deposition of the İhsaniye Formation.