Late campanian-maastrichtian evolution of orbitoidal foraminifera in Haymana basin succession (Ankara, Central Turkey)
In Central Anatolia, a thick sedimentary succession composed of deep-water turbiditic units represented by marl-shale, sandstone, olistostromal horizons and carbonates crops out. This succession constitutes the lower part of so-called Haymana Basin spanning the Santonian (?)/Campanian-Eocene time interval. Evolution of Lepidorbitoides and Orbitoides concerning embryonic features and the initial chamber arrangement has been investigated in the Late Cretaceous part of this succession. Previously unrecognized assemblages of L. campaniensis - "primitive stage" of O. megaloformis of Late Campanian, L. bisambergensis - "advanced stage" of O. megaloformis of Early Maastrichtian and L. socialis - O. apiculata / O. gensacicus of Late Maastrichtian age have been documented with their biometric aspects. A wide range of variation of evolutionary parameters such as embryon size (Li+li) and number of epi-embryonic chambers (E) of the Orbitoides specimens in the same and successive populations has been observed. Existence of primitive Orbitoides (O. media type) embryons in phylogenetically advanced populations is very conspicuous. Concerning the variation in embryonic features (transition from biserial to quadriserial forms in Lepidorbitoides) and evolutionary parameters in Orbitoides (Li+li : Size of embryon, E : Number of epi-embryonic chambers) and Lepidorbitoides (D : Size of deuteroconch; D/P : Ratio of size of deuteroconch to protoconch; a : Number of a adauxiliary chambers) it can be proposed that Lepidorbitoides is more reliable than Orbitoides in aging the populations at least during Late Campanian-Early Maastrichtian time interval.