Benthic foraminifera of the Maastrichtian sediments from the Maliboğazi (Kalecik, Ankara) and Irmak (Kırıkkale) areas in Türkiye

Abstract

The investigation focuses on benthic foraminifera and their paleoecology, particularly on the Orbitoides genus in the Maaastrichtian sediments from the northern and western Ankara City (Turkey). The hard and soft rock samples from two measured sections, namely as Malibogazi (N Ankara) and Daryaka-Irmak (W Ankara, Kirikkale) were evaluated. More than one hundred equatorial and axial sections of the Orbitoides genus were prepared. The benthic foraminifera of the Maastrichtian sediments are as follows: Dorothia sp., Marssonella sp., Lenticulina sp., Saracenaria sp., Oolina sp., Cibicides sp., Gavelinella sp., Orbitoides apiculatus, O. gruenbachensis, O. medius, Pseudomphalocyclus sp., Omphalocyclus macroporus, Lepidorbitoides sp., Sirtina sp., Sulcoperculina globosa, S. vermunti, Siderolites calcitrapoides, Laffitteina mengaudi, Laffitteina sp. In the Malibogazi area, biometric data based on the internal and external parameters of the Orbitoides genus present reliable interpretations for paleoecological approaches of the Maastrichtian time. The calcareous siliciclastics comprise abundant Orbitoides apiculatus and O. gruenbachensis species. We have identified two ichnospecies as Maeandropolydora osmaneliensis and Curvichnus semorbis in the Orbitoides tests. It is thought that meandered microboring activity are related to parasitic life modes while cave shaped ones are associated with hermit type life modes. Orbitoides bearing siliciclastics overlies reefal sediments including biostromal limestones with rich rudist fauna, Thalassoniodes rich carbonates and massive, thick bedded limestones in the Maliboğazi area. In contrast, siliciclastics indicating open sea sediments outcrop widespreadly in the Irmak area. The obtained stratigraphical, sedimantological and paleontological data show that northern part of the Ankara was shallower than western part of the Ankara during the late Maastrichtian.