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Responses of the planktonic foraminifera to environmental conditions across the cretaceous/paleogene boundary in the Göynük basin, Northwest Anatolia, Turkey

Özder, Rengin
The aim of this study is to reveal the evolutionary response of the planktonic foraminifera after the Cretaceous/Paleogene (K/Pg) boundary interval in the Göynük Basin, Northwest Anatolia, Turkey. To achieve this purpose, a multidisciplinary study including biostratigraphy and mineralogy was carried out. In the Göynük area, an 8.55 m-thick section was measured, and a total of 47 samples were collected from the Seben Formation and the Hisarözü member of this formation composed of marls and clayey limestones. In the Göynük section, five biozones were identified in the ascending order; Pseudoguembelina hariaensis Zone, P0, P1a, P1b, and P1c zones. The K/Pg boundary was delineated between the P. hariaensis and P0 zones. In order to study the evolutionary recovery of the planktonic foraminifera, a quantitative analysis was carried out from the samples of the P1b and P1c zones. Results indicate that the r/Kstrategists and r strategists occurred together in the P1b zone, whereas in the P1c zone, K-strategists were totally dominant. Microtektites have been recorded from uppermost Maastrichtian of the Göynük section; microspherules are highly abundant in the P0 zone where the r-strategists are dominant. Mineralogical studies, on the other hand, indicate that clay minerals in carbonate dominated marl samples are kaolinite, Ca-montmorillonite and illite. In the boundary, rutile, ilmenite, zircon, apatite, hematite, micas, hornblende inferring magmatic origin are present. Hg exists in the groundmass. All these microfacies, mineralogical, and geochemical findings, coinciding with the magnetic susceptibility results carried out in this study, might be the evidence of different phases of global Deccan volcanism, the possible cause of the delayed recovery of the planktonic foraminifera following the K/Pg mass-extinction in the Göynük Basin. Furthermore, the presence of the microtektites and microspherules probably indicate the effects of the Chicxulub impact.