Source rock potential and depositional environment of the lower oligocene İhsaniye formation in NW Turkey (Thrace, Karaburun)

Emilia Tulan, Reinhard F. Sachsenhofer, Gabor Tari, Rachel Flecker, Vanessa Fairbank, Magdalena Pupp, Ryan B. Ickert

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The Lower Oligocene succession of the İhsaniye Formation, exposed at Karaburun on the Turkish (Thrace) coast of the Black
Sea, provides insights into potential hydrocarbon source rock extent in the southwestern part of the Black Sea Basin. Presently, no
detailed study of the İhsaniye Formation exists with regards to organic matter content and type. We analyzed 78 fine-grained samples
from a c. 70-m-thick section near Karaburun. Relatively high total organic carbon (TOC) contents (average 1.45 wt.%) are present in
the lower part of the İhsaniye Formation; the hydrogen index values reach a maximum of 252 mg HC/g TOC, indicating the presence of
type III–II kerogen, and the organic matter is thermally immature (Tmax 418 °C). The presence of foraminifera and TOC/S ratios below
2.8 confirm a fully marine environment. Elevated TOC contents and very low pristane/phytane ratios indicate an oxygen-depleted
environment during deposition of the lower part of the İhsaniye Formation. The quartz/clay minerals ratio suggests a deepening trend in
the lower part of the succession and a shallowing trend in the upper part. Peculiarly, the low salinity “Solenovian Event” (in nannofossil
zone NP23) is not developed although Sr isotope ratios indicate that the basin was only connected to the Mediterranean for short
periods during deposition of the İhsaniye Formation.
Original languageEnglish
Pages (from-to)64-84
Number of pages21
JournalTurkish Journal of Earth Sciences
Issue number1
Publication statusPublished - 2 Jan 2020


  • Hydrocarbon source rock
  • Lower Oligocene
  • Paratethys
  • Strontium isotopes
  • West Black Sea Basin

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