A revision of (early) Burdigalian hyaline larger foraminifera based on the biometric study of miogypsinids, lepidocyclinids, and nummulitids from eastern Turkey provides new insights into their taxonomy and paleo-biogeography in the Tethys region. Data from the Adilcevaz Formation show a strong similarity to occurrences from Southeast Asia in that they include Cycloclypeus, Eulepidina, and "ribbed" Nephrolepidina, an assemblage not previously recorded from age-equivalent deposits in the circum-Mediterranean region. The association and the occurrences of these taxa in Lower Miocene deposits from the Indo-West Pacific areas have been widely reported. The species designation of Nephrolepidina and Eulepidina, in the absence of well-demonstrated comparable biometric and conflicting stratigraphic data from the Indo-West Pacific areas, is usually problematic. The Turkish taxa bear a close resemblance to N. sumatrensis and E. formosa, whilst Cycloclypeus is represented by C. eidae, which is widespread in the Indo-Pacific Early Miocene. These axa are accompanied by Miolepidocyclina burdigalensis, a well-documented side branch of the main Miogypsina lineage in the circum-Mediterranean region; Miogypsina globulina, a worldwide tropical species common to both provinces; and Operculina complanata. Our data provide the first foraminiferal evidence from Turkey suggesting a main westward migration of several important groups from Southeast Asia to the eastern Mediterranean during the (early) Burdigalian. This faunal incursion is the most significant compared to other Late Oligocene-Early Miocene foraminiferal events in Turkey.
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