Rock-Forming Nannofossils in Uppermost Jurassic-Lower Cretaceous Rock Units of Northwest Anatolia: Nannoconusand Its Resived Taxonomy

Authors: SEVİNÇ ÖZKAN ALTINER

Abstract: Nannoconids have been recorded in a rock-forming quantity in the uppermost Jurassic-Lower Cretaceous rock units in Northwest Anatolia, Turkey. Samples were collected from seventeen stratigraphic sections spanning the calciturbidities of the Yosunlukbayiri Formation and pelagic micrites of the Sogukçam Limestone. Because of rareness and difficulties for extracting of calcareous nannofossil species particularly zone markers in these type lithologies, nannoconids have particular attention in terms of biostratigraphy. Twenty nine species of nannoconids were recorded in the studied samples. Their taxonomy were revised and their stratigraphic ranges were given. The classification of genus Nannoconusis based on the gross morphology of the test, presence of central cavity or central canal, proportion of central cavity to thickness of the wall, proportion of height to width. Thickness of calcite elements, degree of horizontal intercept angle, type of apertures and degree of horizontal intercept angle, type of apertures, and degree of angle of apertural elements are also used for description of the species. Fluctuations in nannoconid abundance are related to lithological changes. High abundance of nannoconids in limestones indicates clear surface water palaeoenvironments without terrigenous influx. From the stratigraphical point of view, their importance was clarified by their high abundance peaks. Problematic zonal boundaries of the nannofossil zonation could be determined by major nannoconid bioevents.

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