DATE2018-05-28 09:48:00
AUTHORSM Athanasiou (1), MV Triantaphyllou (1), MD Dimiza (1),A Arabas (2), IP Panagiotopoulos (1), K Kouli, A Gogou (3), I Bouloubassi (4), C Panagiotaropoulos (1), E Tsiolakis (5), G Theodorou (1)
  1. National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment, Panepistimioupolis 15784, Athens, Greece
  2. Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, ul. Senacka 1, Kraków 31-002, Poland
  3. Hellenic Centre for Marine Research, Institute of Oceanography, 19013 Anavyssos, Attica, Greece
  4. Laboratoire d'Océanographie et du Climat: Expérimentation et Approches Numériques (LOCEAN/IPSL), Université Pierre et Marie Curie-CNRS-IRD-MNHN, 4 Place Jussieu, Case 100, 75252 Paris, Cedex 05, France
  5. Geological Survey Department of Cyprus, 1 Lefkonos Street, 2064 Strovolos Lefkosia, Cyprus
ABSTRACTThe Kottaphi Hill Section (KHS) on Cyprus Island represents a well-exposed complete sequence of the hemipelagic Pakhna Formation with rhythmically bedded chalks and marls, most probably correlated to all three Earth's orbital parameters and reflecting the Miocene relative sea-level change (e.g., Davies, 2001). The current work aims to provide solid evidence for monsoon-type climatic variability during the Early-Middle Miocene in the Eastern Mediterranean. Seventeen laminated siltstone layers (3–10 cm thick), matching with the precession-scale cyclicity, were found exposed in-between 20.4–42.0 m of KHS and interbedded within 114 chalk / marly chalk / chalky marl alternations. These siltstones may be interpreted as transgressive basin-plain deposits, while the carbonate facies can be considered as hemipelagic sediments of the regressive stages of the relative sea-level change. High-resolution quantitative calcareous nannofossil analysis, performed for this interval, provides correlation with the NN4–NN7 biozones, while additional planktonic foraminiferal bioevents support the identified time framework. The studied sediment sequence is dated between 15.1 Ma (FO Orbulina suturalis at 16.4 m) and 11.6 Ma (LO Discoaster kugleri at 36.7 m). The organic carbon (OC) contents of the thin siltstone units appear quite higher, up to 0.36%, compared to the OC values in the chalk /chalky marl layers (0.17% on average). Carbon and oxygen composition analyses carried out on the planktonic foraminifera Orbulina universa indicate heavier values of δ18O (0.06‰ on average) within the low OC chalk / marly chalk / chalky marl layers. In contrast, for the thin laminated siltstones lighter δ18O signatures (up to -0.95‰) are exhibited, suggesting warmer temperatures and enhanced precipitation. Superimposed oxygen isotope excursions are associated with the Miocene Mi3a-Mi5 events, commonly interpreted as a record of brief glaciations. The positive excursions of the calcareous nannofossil species Discoaster spp., Sphenolithus spp. and Rhabdosphaera spp. within the OC-enriched siltstone layers provide evidence for warm oligotrophic surface waters and stratified conditions coupled with a salinity decrease (increment of Helicospahera spp.), whereas plant remains and palynological evidence suggest fluxes (strong enough to reach the basin-plain realm) of terrestrial organic matter triggered by vigorous river discharges during the monsoon seasons. The foraminiferal content comprising > 90% of the planktonic specimens refers to the lower epibathyal zone, however, the extremely rare benthic forms represented by the oxic-preference taxa Gyroidinoides, Uvigerina, Nodosaria and Hoeglundina indicate a well-oxygenated seafloor. All available evidence propose a shift to monsoonal activity between 15.1-11.6 Ma without, however, the regional depositional and hydrographic regime being appropriate for this signal to be preserved as sapropelic facies in the KHS sediment record.