Microborings as indication of cryptic life modes in the foraminifer Orbitoides: Maastrichtian sediments of the Haymana and Nallihan districts (Ankara, Turkey)

Widespread Maastrichtian siliciclastics and carbonates cropping out in the Haymana (S Ankara) and Nallihan (NW Ankara) districts in the northwest and central Anatolia basins include rich Orbitoides occurrences. Microborings in the Orbitoides tests are interesting to notify. In this study, the details of their morphologic structures were investigated. Microborings were analyzed in more than 650 equatorial thin sections of the Orbitoides tests and 100 hard rock thin sections. The abundance of microborings increases in the siliciclastics towards the Cretaceous/Palaeogene boundary (K/Pg). They were identified as Maeandropolydora osmaneliensis Nielsen and Görmüs, Maeandropolydora isp. Curvichnus semorbis Nielsen, Oichnus simplex Bromley, Oichnus isp. Maeandropolydora osmaneliensis Nielsen and Görmüs. Maeandropolydora isp., semicircular to circular microborings of Curvichnus semorbis Nielsen and Oichnus simplex Bromley are related to parasitic life modes. Irregular wider unidentified microborings are hermit type life mode tunnels. Abundance of the microborings might be related to shallower siliciclastic environmental conditions such as feeding and suitable Eh-pH, test shape, and easy entrance to the test for parasites. Smaller benthic foraminifera are seen in both microspheric and megalospheric Orbitoides tests as parasites. In conclusion, occurrences of microborings and encrustations are associated with parasitism by appearances of Maeandropolydora osmaneliensis Nielsen and Görmüs, Curvichnus semorbis Nielsen and Oichnus simplex Bromley and commensally attachment by microalgae.