A new Messinian Rhodolith Carbonate Stratigraphic Unit from Eastern Mediterranean, Crete, Greece

Neogene strata are widespread in the island of Crete, Greece. They comprise both clastic and carbonate formations, sometimes in alternations. They were deposited in semi-enclosed or open basins developed during extensional periods of the southern Aegean region that prevailed in the Miocene. The present study deals with a significant deposit of calcareous algae, particularly Rhodoliths, that are documented in the western part of Crete, along its northern coastal cliffs, near the city of Chania. These deposits are for the first time described in western Crete and they are considered of great importance for the geologic evolution of this area, while at the same time they provide clues for the paleoenvironmental history of the region and further may be considered, under circumstances, a potential reservoir for hydrocarbons. Rhodoliths are nodular coralline algae, and their eco-preferences' include pure marine, shallow waters, usually of medium to high energy. The studied outrcrop presents a length of almost 2kms and a total thickness of about 45m. The methodology included field and laboratory work. First numerous stratigraphic and sedimentologic logs were taken along the profile. Secondly, photographic documentation of specific horizons enabled us a) to measure the two axes of the Rhodoliths and to construct diagrams as to third, clarify the shape type, b) to investigate the morphology and c) the size, factors that are connected to the water energy of the depositional environment. Two sets of non-cohesive Sandstones represent the basal part of the outrcop, on top of which the Rhodolithic Unit was gradually developed. The latter is subdivided into seven successive cycles of Rhodoliths/coralline crusts-marly sandstones (a bindstone and a coralline floatstone), in alternations, of about 1 to 2 meters each. Following our results, their structure and appearance in addition to the sedimentologic/stratigraphic observations of the logs and the structures is interpreted to be related to a sequence stratigraphic transgressive–highstand system tract (TST, HST) of relative sea-level changes. The upper part of the outcrop is unconformably (Sequence Boundary, SB) overlain by a heavily indurated bioclastic limestone, which partly includes red algae and Lamellibranch fragments within its structure. The whole deposition of the Rhodoliths Unit is considered a slightly dipping carbonate ramp which pre-dated the Messinian Salinity Crisis (MSC) event of the Mediterranean, during which it is believed that the prementioned marine shallow water limestone was deposited. Finally, a correlation of the new occurrence and of similar age deposits is presented for the Mediterranean, based on well-known distribution maps.