Late Ypresian to Middle Lutetian Orthophragminid Record From Central and Northern Turkey: Taxonomy and Remarks on Zonal Scheme

Authors: ERCAN ÖZCAN, GYÖRGY LESS, BOTOND KERTESZ

Abstract: Orthophragmines are one of the commonest larger foraminifera in the late Paleocene-Eocene shallow-marine deposits of Turkey. Following several common lineages, such as Discocyclina archiaci, Orbitoclypeus schopeni and O. multiplicatus, a major turnover in the orthophragminid composition - both in diversity and abundance - is observed to occur around the early-late Ypresian boundary. This is manifested in the first appearance/dominance of such important lineages like Discocyclina augustae, D. fortisi, Nemkovella strophiolata, Orbitoclypeus douvillei, O. varians, O. furcatus, Asterocyclina stellata and A. alticostata simultaneously with the disappearance of O. multiplicatus and other forms. These and their successors, ranging up at least to the middle Lutetian, have been studied and statistically evaluated in the equatorial sections of their megalospheric forms. The identified forms are categorized into evolutionary lineages, in which different developmental stages are distinguished by biometrically defined subspecies. Based mainly on the Turkish record, the evolutionary track of several little known western Tethyan lineages could be completed and redescribed in the late Ypresian to middle Lutetian interval. Also introduced and newly established are four new subspecies; two new subspecies of Discocyclina, D. fortisi anatolica n. ssp. and D. spliti polatliensis n. ssp. from the late Ypresian and early Lutetian respectively, one subspecies of Nemkovella, N. evae karitensis n. ssp. and one of Orbitoclypeus, O. varians ankaraensis n. ssp., from middle and early Lutetian, respectively. An emended diagnosis of O. munieri is also given. As a result, the taxonomy of western Tethyan orthophragmines has been updated and the stratigraphic distribution of some taxa is rearranged. The definition of some previously assigned orthophragminid zones (OZ 7, 8a and 8b) were completed and simultaneously recalibrated in the context of the shallow benthic zonation of the Tethyan Early Paleogene.

Keywords: Turkey, Eocene, Discocyclinidae, Orbitoclypeidae, Biometry, Evolution, Zonation

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