Integrated micropalaeontological study (ostracods and calcareous plankton) of the Langhian western Hyblean successions (Sicily, Italy)

Four sections cropping out in the Hyblean Plateau (SE Sicily) were studied biostratigraphically and palaeoecologically. The investigated succession was referred to the early–late Langhian on the basis of both the planktonic foraminifers (lowermost part of the Praeorbulina glomerosa sicana Subzone–lowermost part of the Orbulina universa Subzone) and the calcareous nannofossils (uppermost part of the MNN4a Zone–lowermost part of the MNN5b Subzone). All the biozonal markers were recorded and further significant events were identified. The most remarkable ones are two paracmes of Paragloborotalia siakensis within the P. glomerosa sicana Subzone and the distribution of Helicosphaera waltrans, which characterises the upper part of the MNN5a Subzone. The ostracod palaeoecological analysis indicated a progressive and gradual trend from thermospheric to psychrospheric conditions and probably a basin deepening (from upper to lower epibathyal). The flowing of deep Atlantic waters into the basin is documented by the entry of the psychrospheric species Agrenocythere hazelae within the upper part of the P. glomerosa sicana Subzone. Only in the late Langhian, however, were typical psychrospheric conditions probably reached. These data provide evidence that oceanic deep water masses reached the Central Mediterranean, passing through both the western connections to the Atlantic Ocean and the African–Sicilian threshold, during a great part of the Langhian.