The calcareous nannofossil record of the uppermost Maastrichtian-lower Palaeocene in the Kırıkkale Basin, in the Central Anatolian Region (Turkey)

The Late Cretaceous–Early Paleogene (K–Pg) was a critical period of transition in geological time. This period encompassed short-term climatic fluctuations on a global scale, changes in ocean circulation, and sudden and large extinctions of marine and terrestrial organisms. In the study area, located in the mid to low latitudes, the Late Cretaceous and Early Paleogene were very tectonically active due to the positioning of the site close to the collision zone of two large continents. The impacts of the global K–Pg crisis can be observed in the study area. In this study, the calcareous nannofossil contents of late Maastrichtian–Danian sediments were studied, and the nannofossil biostratigraphy determined, from samples from the Samanlık and Dizilitaşlar Formations, deposited in the Kırıkkale Basin. From three stratigraphic sections, 26 nannofossil genera and 36 nannofossil species were identified from the Late Maastrichtian UC20aTP and UC20bTP biozones and the NP1 and NP2 biozones of the Danian. Additionally, it was determined that the K–Pg boundary was not continuous in the study area. In the Kırıkkale Basin, relatively low abundances of Micula decussate Vekshina, 1959 signals a diagenetic effect and stressful environment in the Late Maastrichtian, whereas the relatively low abundances of Thoracosphaera operculata Bramlette & Martini, 1964, Braarudosphaera bigelowii (Gran & Braarud, 1935) Deflandre, 1947 and Futyania petalosa (Ellis & Lohmann, 1973) Varol, 1989 in the Danian assemblages indicate unstable environmental conditions and major environmental perturbations that reflect tectonic activity in the region. No nannofossils were encountered in those samples taken from turbiditic levels, which contained high proportions of sand.