Early Pliocene deposits in Kephallonia (Ionian Islands): Biostratigraphy and paleoenvironmental-paleoclimatic implications

The island of Kephallonia is located in the eastern part of the Ionian Sea, off the shores of Western continental Greece. The Paxos geotectonic unit comprises the largest part of the island, while in the eastern part outcrop the Ionian unit sediments. The studied marly limestones and marls in Livadi (approx. 30 m thick) are located on the northeastern part of Paliki peninsula, north of the city of Lixouri. Katelios section (approx. 70 m thick) located at the southeastern coast of the island, consists of marls alternating with sandy layers and marly limestones. The exposed sediments at Livadi represent part of the latest synorogenic deposits of Paxos unit, corresponding to the Trubi limestones above the Messinian evaporites. Katelios sequence is located immediately below the Ionian thrust on Kephallonia Island and could comprise the continuation of the Livadi sequence. Micropaleontologicala analyses (calcareous nannofossils, dinoflagellates and foraminifera) have been performed on both studied outcrops in order to determine their age and investigate the paleoenvironmental and paleoclimatic depositional conditions.
   Calcareous nannofossil biostratigraphy revealed a number of biovents establishing the chronostratigraphic correlations of the studied deposits. In the sediments of Livadi section, the presence of Sphenolithus spp. (abundance >5%), several discoasterid species (Discoaster brouweri, D. pentaradiatus, D. surculus, D. intercalaris, D. variabilis) and abundant planktonic foraminiferal species Sphaeroidinellopsis spp. along with the moderate presence of Amaurolithus spp. and Reticulofenestra pseudoumbilicus (abundance 1-2%) documents the biostratigraphic correlation with the nannofossil biozone NN12. Livadi outcrops are more precisely assigned within the Sphaeroidinellopsis Acme Zone, just below the Paracme Zone of R. pseudoumbilicus. Therefore they are of Early Zanclean age, ranging between 5.30-5.21 Ma. The sequence of Katelios section is featured by the dominance of R. pseudoumbilicus (abundance >20%), the presence of Pseudoemiliania lacunosa and Discoaster asymmetricus, D. pentaradiatus, D. surculus, that enable the biostratigraphic assignment within the NN14- 15 nannofossil biozone (4.12-3.839 Ma) during the Late Zanclean.
   The dynamics of calcareous planktonic and benthic communities are of paramount significance in estimating the palaeoenvironmental conditions because they quickly respond to oceanographic changes (primary production, water stratification, temperature, salinity, etc.).
   Warm surface water conditions in a pelagic environment are assumed for the interval just above the Miocene-Pliocene boundary (uppermost synorogenic sediments of Paxos unit, Livadi section), as documented by the nannofossil assemblages and the well developed planktonic microfauna. In particular the presence of discoasterids, Rhabdosphaera spp., Sphenolithus spp., Scyphosphaera spp., Amaurolithus spp., R. pseudoumbilicus, Sphaeroidinellopsis spp. and the calcareous dinoflagellate Thoracospharea heimi is indicative of warm subtropical conditions. Relatively increased productivity is implied by the presence of Helicospaehera spp., which is known to preferentially high productivity waters in the middle photic zone. In this study, the genus Helicosphaera is represented mainly by H. carteri, a species with preference in warm waters and moderately elevated nutrient levels.
   The Late Zanclean deposits of Katelios section are associated with a shallow depositional environment marked by the presence of abundant benthic foraminifera. The nannofossil assemblages indicate warm-temperate and high-productivity conditions due to the abundance of R. pseudoumbilicus. Additionally the dominating discoasterid species (abundance >5%) D. pentaradiatus, D. asymmetricus, D. brouweri favour warm and more productive intervals, in contrast to rare D.variabilis and D. surculus which are mostly associated with colder conditions.