Planktonic foraminiferal diversity and abundance changes across cretaceous-paleogene boundary beds in the Haymana basin and new observations on the extinction horizon

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2017
Karabeyoğlu, Ali Uygar
Abundance and diversity patterns in planktonic foraminifera are important for paleoenvironmental and paleoclimatic interpretations before and after the CretaceousPaleogene mass extinction. A 14,53 m thick section was measured crossing the boundary between the Haymana Formation and the Yeşilyurt Formation in the northern part of the Haymana Basin. In the last 3.75 meters of the Maastrichtian below the K-Pg boundary, a series of quantitative analyses were carried out on planktonic foraminifera found above 63 and 150-micron screen sizes. By using foraminiferal bioevents, biozones were established which are: Plummerita hantkeninoides Zone for the uppermost Maastrichtian; P0 and Parvularugoglobigerina eugubina zones for the base ofthe Danian. Additionally, paleobathymetry of the measured section was studied with the help of planktonic-benthic ratios. Calculations indicate approximately 400 m water depth for the depositional environment. Identification of deep water dweller planktonic foraminifers in the studied section, such as Planoglobulina multicamerata and Gublerina cuvillieri also supports this result. Quantitative analyses resulted that at the end of Maastrichtian, Heterohelix species, which are tolerant to temperature, nutrient, oxygen and salinity fluctuations, dominated (~40%) the environment while those which are not resilient such as Globotruncana species remained low (~10%). On the other hand, Guembelitria cretacea, which show opportunistic blooms during environmental crisis and dwell at the surface of the water column, survived from the K-Pg mass extinction. This study, for the first time in Turkey, shows blooms of Guembelitria cretacea in the Haymana Basin for the latest Maastrichtian and right after the K-Pg boundary in P0 Zone. Right after the K-Pg boundary, the first samples of the Danian P0 Zone are characterized by Thoracosphaera acme whose diameters are ranging between 10 to 20 microns. In addition to that, another sharp increase was also found in echinoid fecal pellets which peak at 2 cm above the boundary. Previously, the same pellet increment was recognized in the southern part of the basin. These discoveries support the idea of ''Echinoid fecal pellet peak as a K-Pg boundary marker''. In the Haymana Basin, Maastrichtian mudstones are overlain by marls and calcareous mudstone alternations in the Danian indicating a major change in the depositional regime after the K-Pg boundary. A similar stratigraphy has also been observed in the Mudurnu-Göynük Basin in the K-Pg boundary beds. This similarity in an interval of high chronostratigraphic resolution brings the possibility whether these two basins were connected to each other during end Cretaceous and the beginning of Paleocene.

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Citation Formats
A. U. Karabeyoğlu, “Planktonic foraminiferal diversity and abundance changes across cretaceous-paleogene boundary beds in the Haymana basin and new observations on the extinction horizon,” M.S. - Master of Science, Middle East Technical University, 2017.