Deep sea benthic foraminiferal diversity and abundance changes across cretaceous-paleogene boundary beds in the Haymana basin (Ankara, Turkey): paleoenvironmental implications

Vardar, Ezgi
In order to establish the taxonomy of deep-sea (small) benthic foraminifera and to evaluate their paleoenvironment and paleoecology in terms of relative abundances and diversity, a 14.53 meters-thick section was measured from the Haymana Formation and the Yeşilyurt Formation containing Cretaceous-Paleogene boundary beds in the northern part of the Haymana Basin, Central Turkey. 17 mudstone samples corresponding to 3.15 meters of the upper Maastrichtian and 8 mudstone-marl samples representing 1.21 meters of the lower Danian were studied in detail, around 300 benthic foraminifera individuals were picked from >125 μm fraction for each sample. Three biozone were established for the first time from Turkey; which are Bolivinoides draco Zone and Eouvigerina subsculptura Acme Zone (newly proposed) for the Maastrichtian and BB1 Zone for the Danian. As a part of the quantitative assessment, morphogroup analysis were performed with intent to infer infauna-epifauna ratio. Calcareous and agglutinated taxa were categorized into 15 morphogroups overall. Calcareous taxa are assigned as CI1 (cylindrical tapered), CI2 (flattened tapered), CI3 (rounded planispiral), CI4 (spherical) for infaunal group and CE1 (planoconvex trochospiral), CE 2 (biconvex trochospiral), CE3 (rounded trochospiral), CE4 (palmate), CE5 (branching) for epifaunal groups. Agglutinated taxa were sorted by AI1 (elongate multilocular), AI2 (flattened trochospiral), AI3 (elongate tapered) for infaunal groups and AE1 (coiled flattened & streptospiral), AE2 (elongate keeled), AE3 (tubular-branching) for epifaunal groups. Morphogroup analysis shows that the relative abundance of infaunal groups make up average 75% of the total Maastrichtian assemblage. This relatively high infaunal abundance suggests meso- to eutrophic conditions accordingly with the presence of common species preferring high nutrient levels. Quantitative analysis also showed that calcareous taxa is more abundant with respect to agglutinated taxa, with relative abundance of average 73.9% in Maastrichtian and average 89.0% in Danian, offering a depositional setting well above the Calcium Carbonate Compensation Depth (CCD). Moreover, open marine conditions and upper bathyal environment (~200-600m) are suggested for the whole studied section based on the benthic foraminiferal diversity and associations. A remarkable change from highly diverse Maastrichtian benthic foraminifera assemblage to poor-moderately diverse Danian benthic foraminifera assemblage is assessed at the transition from the Haymana Formation to the Yeşilyurt Formation. This change is revealed for the first time in Turkey and associated with disappearance of 53% of Maastrichtian taxa as well as the high abundance of epifaunal taxa (average 75.8%) after the boundary which possibly resulted from decline of primary productivity at the K-Pg boundary.
Citation Formats
E. Vardar, “Deep sea benthic foraminiferal diversity and abundance changes across cretaceous-paleogene boundary beds in the Haymana basin (Ankara, Turkey): paleoenvironmental implications,” M.S. - Master of Science, Middle East Technical University, 2018.