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Organic-carbon deposition in the Cretaceous of the Ionian Basin, NW Greece: the Paquier Event (OAE 1b) revisited

HARILAOS TSIKOS^*,, VASILIOS KARAKITSIOS, YVONNE VAN BREUGEL, BEN WALSWORTH-BELL^¶, LUCA BOMBARDIERE^||, MARIA ROSE PETRIZZO^¶, JAAP S. SINNINGHE DAMSTÉ, STEFAN SCHOUTEN, ELISABETTA ERBA^¶, ISABELLA PREMOLI SILVA^¶, PAUL FARRIMOND^||, RICHARD V. TYSON^|| and HUGH C. JENKYNS^*

^* Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK
Department of Geology, University of Athens, Panepistimiopolis 15784, Athens, Greece
Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research (NIOZ), 1790 AB Den Burg, The Netherlands
^¶ Department of Earth Sciences ‘Ardito Desio’, University of Milan, Via L. Mangiagalli 34, 20133 Milano, Italy
^|| NRG, School of Civil Engineering & Geosciences, Drummond Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK

Author for correspondence: h.tsikos{at}abdn.ac.uk; present address: Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, UK.

We present new stable (C, O) isotopic, biostratigraphic and organic geochemical data for the Vigla Shale Member of the Ionian Zone in NW Greece, in order to characterize organic carbon-rich strata that potentially record the impact of Cretaceous Oceanic Anoxic Events (OAEs). In a section exposed near Gotzikas (NW Epirus), we sampled a number of decimetre-thick, organic carbon-rich units enclosed within marly, locally silicified, Vigla Limestone (Berriasian–Turonian). All these units are characterized by largely comparable bulk geochemical characteristics, indicating a common marine origin and low thermal maturity. However, the stratigraphically highest of these black shales is further distinguished by its much higher total organic-carbon (TOC) content (28.9 wt%) and Hydrogen Index (HI) (529), and much enriched ¹³Corg value (–22.1). Planktonic foraminiferal and calcareous nannofossil biostratigraphy indicate a lower to middle Albian age for the strata immediately above, and a lower Aptian age for the strata below, the uppermost black shale. In terms of molecular organic geochemistry, the latter black shale is also relatively enriched in specific isoprenoidal compounds (especially monocyclic isoprenoids), whose isotopic values are as high as –15, indicating a substantial archaeal contribution to the organic matter. The striking similarities between the molecular signatures of the uppermost Vigla black shale and coeval organic-rich strata from SE France and the North Atlantic (ODP Site 1049C) indicate that this level constitutes a record of the Paquier Event (OAE 1b).

Key Words: Cretaceous • Albian • stratigraphy • isotopes • carbon

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