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International audienceEnvironmental change significantly affects the production of fish resources and their dependent societies. The paleontological record offers unique insight into the effects of long-term paleoenvironmental variability on the fish species’ distributions and abundances. In the present study, we investigate the late Miocene (7.5–6.5 Ma) fish assemblages of the Potamida section in western Crete (eastern Mediterranean). The determined fish taxa are examined in a paleobiogeographic context, with regard to their geographic and stratigraphic distribution from the early Miocene (~13 Ma) through today. In addition, present-day ecological data are used to reconstruct the paleoenvironmental conditions in the study area. Planktonic foraminifer biostratigraphy significantly improves the earlier dating of the studied sequence. The late Miocene fish fauna of Potamida includes 35 taxa (seven in open nomenclature) from 13 teleost families. The eastern Mediterranean biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Tortonian, whereas 13 species are recorded for the first time from the Messinian. Four stages are distinguished in the area’s paleoenvironmental evolution. (1) The Potamida area was an open marine environment with depths exceeding 150 m between ~7.5–7.45 Ma. (2) Between 7.45–7.36 Ma, the results suggest depths between 300–400 m. (3) The depositional depth increases between 7.36–7.28 Ma to 400–550 m. (4) Later on, approximately between 6.8–6.6 Ma, the depth is again estimated around 100–150 m

This study details new geochemical analysis from an outcrop in Crete to improve understanding of the hydrocarbon potential of the southern margin of the Hellenic Arc along the continental convergent zone of the central Mediterranean Ridge. Seventeen samples were collected from the Late Miocene sub-salt sedimentary succession of Plouti section in central Crete and were studied in terms of their organic geochemical features using Rock-Eval VI pyrolysis. Results of this investigation revealed intervals with sufficient organic material of good enough quality and quantity to be considered as potential source rocks. The obtained data generally present poor to fair and/or good in some cases hydrocarbon generation potential. The TOC values range from 0.03 to 1.99%, with an average fair (2.1 mg HC/g rock) hydrocarbon potential. A Type III kerogen was identified, indicating a terrestrial origin organic matter. T max and Production Index values suggest that the most promising parts of the section (organic-rich sediments) are immature with respect to oil generation and have not experienced high temperature during burial. Overall, the present study offers the opportunity to advance our understanding on the hydrocarbon potential onshore Crete and further investigate hydrocarbon prospectivity in the adjoining area, and particularly, the Greek part of the Mediterranean Ridge, a region with crucial economic and strategic importance.

Re´sume´-Roche-me`re potentielle du Messinien pre´-e´vaporitique d'un basin adosse´a`l'ensemble de fosses helle`niques (Messara, Cre`te central, Gre`ce) -Le secteur grec de la Ride Me´diterrane´enne, vu son potentiel en hydrocarbures, demande une exploration frontalie`re prononce´e. Les similitudes ge´ologiques entre ses parties prolifiques, incluses dans les zones e´conomiques exclusives chypriote et e´gyptienne, indiquent des re´serves possibles et re´cupe´rables de gaz naturel dans la partie de la zone e´conomique exclusive grecque. Ne´anmoins, et jusqu'a`pre´sent, il manque une e´tude frontalie`re syste´matique, bien que des indices directs pe´troliers existent. Plusieurs volcans de boues actives sur la Ride Me´diterrane´enne, e´mettant constamment du gaz et des hydrates de gaz, n'ont pas encore e´te´e´tudie´s, quoiqu'en ge´ne´ral, dans le monde entier, ils sont fortement lie´s a`la pre´sence d'hydrocarbures (par exemple dans la Mer Caspienne, le Golfe du Mexique, le Bassin Africain Occidental, a`Trinite´-et-Tobago et dans le coˆne du Nil). Pour cette raison, la roche me`re potentielle dans les successions se´dimentaires du Mioce`ne Supe´rieur d'un bassin 'back-stop' du syste`me du Sillon Helle´nique (bassin de Messara, Cre`te centrale, Gre`ce), a e´te´e´tudie´e. Les donne´es de la pyrolyse indiquent que la teneur en matie`re organique est suffisante et avec une qualite´assez bonne pour la conside´rer comme une roche me`re potentielle. En outre, le type du ke´roge`ne III, sugge`re un potentiel de gene`se de gaz. Meˆme si des indications d'une e´volution thermique plus e´leve´e existent, les roches e´tudie´es te´moignent d'un faible niveau de maturation. Des suintements de gaz bioge´nique dans la re´gion e´tudie´e de´montrent le potentiel re´gional de ge´ne´ration de gaz.Abstract -Pre-Messinian (Sub-Salt)

The aim of this study is to identify the chemical and physical characteristics in uncultivated soils derived from different parent materials under semiarid Mediterranean climatic conditions which favoured the formation of fragile soils. The current work is of great interest in the agriculture and environmental stakeholders for providing a "benchmark" of undisturbed soil quality regarding organic content and nutrients availability. Principal Component Analysis (PCA) was used as the primary tool to demonstrate the soil quality stage, regarding nutrient availability. The statistical analysis revealed that one of the major physicochemical characteristics such as cation exchange capacity (CEC) is controlled exclusively from mineralogy and not from organic matter. Mineralogy and bulk chemical analysis is directly related to soil parent material lithology. The availability of inorganic nutrients (macro-and micronutrients) is low and relatively identical to most of the soils. PCA shows the unusual correlation of K + with not only illite content but also the OM in soils. The development of soils which are already of low quality in respect of organic content and nutrients is evident in Crete in most of the 54 samples investigated.