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ABSTRACT: New biomarker evidence is presented that constrains the conditions of deposition and preservation of sediments rich in extractable organic matter from the Aptian–Albian sedimentary record of the Ionian Zone in NW Greece. Analyses were specifically carried out on total lipid extracts from 12 organic rich samples from the Vigla Shale Member, two of which represent the regional record for the early Albian Paquier Event of OAE1b. In the aliphatic fractions, compound groups such as n-alkanes, isoprenoid alkanes, steroids, hopanoids and terpenoids were recognized, pointing to a mixed origin from algae and prokaryotes with an additional measurable contribution from terrigenous plant matter. These compounds suggest deposition of the primary organic sediments under conditions of decreased bottom water oxygen concentrations. Mass spectral evidence from the aromatic fractions of most samples reveal the variable presence of diagenetic and catagenetic derivatives of carotenoid pigments (including some with bound sulfur) that are characteristic of photoautotrophic sulfur bacteria. The presence of specific biomarkers originating from photosynthetic anaerobic microorganisms, similar to those in ancient and contemporary euxinic basins such as the Black Sea, suggest that photic zone euxinic conditions were intermittently operative in the Aptian–Albian stages of the Ionian Basin, but were not exclusively characteristic of the black shale representing the Paquier Event itself.Organic Geochemistry 11/2013; 64:84-93. DOI:10.1016/j.orggeochem.2013.08.013 · 3.07 Impact Factor
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ABSTRACT: The purpose of this study is to describe the Miocene-Pliocene microfaunal development, and to discuss its palaeoenvironmental and palaeogeographical significance. The studied section (Kalamaki section) is located in the eastern part of Zakynthos Island (western Greece). Details on lithology and stratigraphy of the section are given in Dermitzakis (1978) and Nikolaou (1986). Planktonic species indicate that sediments span the interval which corresponds to MPL1 Zone (Zanclean, early Pliocene) which is in accordance with the biostratigraphic configuration of Rouchy et al. (1992) and Pierre et al. (2006). The studied interval is characterized by the Sphaeroidinellopsis Acme Zone and the presence of Globorotalia margaritae. The recognized succession of microfossil assemblages serves to interpret the evolution of some palaeoenvironmental factors (waterdepth, salinity and oxygen content), whereas the planktonic foraminiferal zonation allows an age assignment to the events. During the Late Messinian brackish conditions became dominant. The early Pliocene is characterized by a sudden return to well oxygenated, open marine, outer shelf conditions. At the basal part of the record, the high abundance of the 'shallow water component' of the benthic foraminiferal fauna indicates a well-vegetated environment with either normal marine salinity or a tendency to hyposalinity (e.g. Murray, 2006). Open marine conditions are indicated by the diversity of benthic and planktonic foraminifera. The abundance of Lenticulina spp., Cibicidoides pseudoungerianus, Planulina ariminensis, Pullenia, Gyroidina, and the virtual absence of Cibicidoides dutemplei and other typical shelf-taxa, suggest an upper bathyal waterdepth of 300-400 m (cf. Pujos, 1976; Jorissen, 1988). Partly, the abundance of Cibicidoides pseudoungerianus, Bulimina costata and Uvigerina peregrina reflect fluctuations in oxygen content of the bottom waters. However, extreme conditions were never reached during deposition. The foraminiferal facies distribution in the studied part of the Kalamaki section is in accordance with isotope oxygen data from basins in the central and eastern Mediterranean basin which indicates the existence of a salinity gradient during this time span. Ostracod fauna is characterised by low diversity and abundance. It is consisting mainly of Bythocypris and Cytherella species, which confirm the bathyal depositional environment. The study of the late Messinian-Early Pliocene sediments in Zakynthos island (Kalamaki section) correlated with time equivalent sections in Crete (e.g. Drinia et al., 2007) and the comparison with the offshore coeval deposits drilled in the ODP Leg 160 boreholes, illustrate the environmental changes which occurred in the Eastern Mediterranean at the end of the salinity crisis. References Dermitzakis, M.D., 1978. Stratigraphy and sedimentary history of the Miocene of Zakynthos (Ionian Islands, Greece). Ann. Geol. Pays Hell., 29:47 186. Drinia, H., Antonarakou, A., Kontakiotis, G., 2007. On the occurrence of Early Pliocene marine deposits in the Ierapetra Basin, Eastern Crete, Greece. Bulletin of Geosciences, 83 (1), 63-78. Jorissen, F.J., 1988. Benthic foraminifera from the Adriatic Sea: principles of phenotypic variation. Utrecht Micropaleontological Bulletins, 37, 1-174. Murray, J., 2006. Ecology and applications of Benthic foraminifera. Cambridge University press, 426pp. Nikolaou, K.A., 1986. Contribution to the knowledge of the Neogene , the geology and the limits of the Ionian and Preapulian zones, in relation to the petroleum exploration , observations in Strofades , Zakynthos and Kefallinia islands. The doct. University of Athens. Pierre, C., Caruso, A., Blanc-Valleron, M., Rouchy, J. M., Orzsag-Sperber, F., 2006. Reconstruction of the paleoenvironmental changes around the Miocene-Pliocene boundary along a West-East transect across the Mediterranean. Sedimentary Geology 188-189, 319-340. The Messinian Salinity Crisis Revisited. Pujos, M., 1976. Ecologie des foraminifères benthiques et des thé-camoebiens de la Gironde et du plateau continental Sud-Gascogne: application á la connaissance du Quaternaire terminal de la région Ouest-Gironde. Memoires de l' Institut de Géologie du Bassin d', Aquitaine, 8, 1-274. Rouchy, J.-M. & Saint Martin, J.-P., 1992. Late Miocene events in the Mediterranean as recorded by carbonate-evaporite relations. Geology, 20: 629-632.