First evidence for the early Aptian Oceanic Anoxic Event (OAE1a) from the Western margin of the Pindos Ocean (NW Greece)

In this paper, new biostratigraphic, stable isotope (C, O) and organic geochemical data are presented for the Pindos Zone in NW Greece (SE Epirus region) in order to investigate whether the organic carbon rich strata of the Kalarrytes sections A and B correspond to a local expression of the early Aptian Oceanic Anoxic Event (OAE 1a or Selli Event) or not. The Pindos Zone Mesozoic to Tertiary sedimentary sequence constitutes the deep-sea sedimentary cover of the Pindos Ocean, which was separated from its oceanic basement as an accretionary prism during the complete closure of this ocean, and was emplaced westwards onto the adjacent Gavrovo-Tripolis carbonate platform. Stable carbon and oxygen isotope data from the Kalarrytes sections reveal an isotopic composition compatible with the characteristic features of the OAE 1a. Calcareous nannofossil and radiolarian biostratigraphy indicates an early Aptian age for both sequences. Biomarker analysis on the organic-rich intervals reveals the primary marine origin of the organic matter, with substantial contribution from bacteria, cyanobacteria and dinoflagellates, as well as a significant terrigenous input. Findings of authigenic framboidal pyrite provide evidence for the prevalence of sulphidic conditions during deposition. Furthermore, similarities between the biomarker signatures of the Pindos organic-rich strata and coeval strata of early Aptian age where the impact of OAE 1a has previously been recorded, are identified. The presented data show that the organic-rich intervals of both Kalarrytes sections constitute the first records of the OAE 1a in oceanic deposits of Greece.