Late Miocene Formations from As Sahabi area, Sirt Basin, Libya in correlation to isochronous SE Europe deposits: A paleoclimatic approach

As Sahabi area has yielded a rich Neogene vertebrate fauna that aids in understanding evolution and paleoenvironments. Stratigraphically, it consists of three stratigraphical superposed lithological units, from bottom to top; Formation "M", Formation "P" and Sahabi Formation. Formation "M" which forms the base of the exposed section in the As Sahabi area consists of semi-consolidated sandy bioclastic carbonates enriched by warm water organisms such mollusks, bryozans, and corals. The presence of the ostracodes and the foraminifera are strong indicators of shallow warm environments. Formation "P" consists of a lattice of monocrystalline gypsum crystals infilling dessicated cracks of siliclastic clays and sands, with no in-situ fauna reported so far. Formation "P" has been attributed to the Messinian crisis in the Mediterranean. These two formations are followed by the vertebrate fossil-bearing rock unit called the Sahabi Formation, which displays a different depositional setting of continental to semi-continental terrestrial tropical paleoenvironments through fluviatile, lacustrine and deltaic water bodies. Two subsurface boreholes from As Sahabi area (Sirt Basin) have been investigated lithologically and micropaleontologically. The upper siliclastic part of these wells is assigned to Sahabi Formation. The lower thin carbonates are assigned to both Formation “M” and Formation “P”. Two subsurface boreholes (A1-NC214 water well and Sahabi Borehole 1-2) have been lithologically described and investigated for their micropaleontological content. The carbonates at the lower depths belong to Formations “M” and “P” respectively. The microfossil bearing interval of the A1-NC214 water well (interval between 165 and 175m) contains rather well preserved calcareous nannofossil assemblage with common-abundant Helicosphaera stalis and Reticulofenestra pseudoumbilicus, accompanied by Coccolithus pelagicus, Calcidiscus macintyrei, Helicosphaera carteri, Sphenolithus moriformis, Discoaster cf. calcaris, Discoaster cf. challengeri. The increased relative abundance of H. stalis (>10%) implies a biostratigraphic correlation with nannofossil biozone NN8/MNN8b, i.e. the interval of common presence of H. stalis below the First Occurrence of Discoaster bellus group. Therefore the carbonates below the Sahabi Formation, at 165m below the surface, are assigned to early Late Miocene (Early Tortonian), ranging between 10.71-10.40 Ma. Concerning Sahabi Borehole 2 the microfossil bearing interval (interval between 72 and 100m) contains a well preserved nannoflora marked by the presence of Discoaster neoerectus, D. berggrenii, D. bellus, Helicosphaera stalis, Reticulofenestra pseudoumbilicus, Calcidiscus miopelagicus, and therefore is assigned to Late Tortonian nannofossil biozones NN10b-NN11a. The First Occurrence of D. berggrenii recorded within this interval provides a datum event with a fixed age of 8.23 Ma. The presence of common Mediterranean benthic foraminifer Borelis melo along with a few planktonic representatives indicates a shallow marine environment and warm paleoclimatic conditions. The abundance of large specimens of R. pseudoumbilicus is indicative of warm and stratified waters. Several Greek marine sites span the Tortonian-Messinian time interval providing a useful framework for biostratigraphic correlations in the eastern Mediterranean area, e.g. Potamos section/northern part of Gavdos island (NN6 - NN9, 13.28-9.61 Ma), Vassiliki section/E. Crete (NN9, 10.18-9.61 Ma), Skoloudhiana section/W. Crete (NN11, 8.68-7.41 Ma), Kastelli section/central Crete (NN11, 8.68-6.79 Ma), Limin Keri section/southern coast of Zakynthos (NN9, 10.18-9.53 Ma), Ag. Sostis section/southern coast of Zakynthos (7.22-6.52 Ma), Kokkino Rema section/ southern part of Kassos island (NN11, 6.79-5.35 Ma). Although none of these locations bears any terrestrial fauna like the Libyan site, based on their micropaleontological content they confirm the warm climatic conditions prevailing during that time. A particular location that contains vertebrate fauna of equivalent age (including primates) is the Axios Valley in northern Greece.