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BORINGS IN LARGER BENTHIC FORAMINIFERS FROM TURKEY AND THEIR PALEOENVIRONMENTAL SIGNIFICANCE

Muhittin Görmü¹ and Jan Kresten Nielsen²

¹ SDÜ Mühendislik-Mimarlik Fakültesi, Jeoloji Mühendislii Bölümü, 32260 Çünür-Isparta, Turkey. E-mail: muhittin{at}mmf.sdu.edu.tr
² INCREMENTS Research Group, Institute of Geology and Paleontology, J.W. Goethe University Frankfurt a.M., Senckenber-ganlage 32-34, D-60325 Frankfurt a.M., Germany. E-mail: bioerosion{at}yahoo.dk

Cretaceous/Paleogene outcrops of Turkey provide important areas for the study of trace fossils on larger benthic foraminiferal tests such as Orbitoides and Loftusia from the Maastrichtian, and Nummulites, Assilina and Discocyclina from the Eocene. The current investigation synthesizes previous and new records of borings on Upper Cretaceous and Paleogene foraminifers with information on faunal associations, stratigraphical correlation and paleoenvironmental conditions. The types of borings were distributed according to their shallow-water paleoenvironments.

Orbitoides tests in siliciclastic sandstones and calcarenites from northwestern and eastern Turkey contain four forms of borings: semicircular tubes, circular cavities, subspherical cavities and undulating tubes. Benthic foraminiferal associations confirm the Maastrichtian age of the borings. Towards the end of the Cretaceous, a regression took place during the Maastrichtian in the Osmaneli area, resulting in a shallower, bivalve-dominated facies. During initial phases of the regression, semicircular tubes and circular cavities were formed, while later phases of the regression led to the formation of undulating tubes. The Loftusia tests from southeastern and eastern Turkey contain cylindrical holes, paraboloid pits and subspherical cavities formed as predational and dwelling borings.

Borings occur on the Eocene larger foraminifera Nummulites, Assilina and Discocyclina from the Ypresian to Bartonian carbonates and siliciclastic sediments in southwestern Turkey. These Eocene sediments comprise back-reef, nummulite-bank, fore-reef and open-sea facies. The benthic foraminifers may contain borings such as cylindrical holes, paraboloid pits, subspherical cavities and spiral tubes. The Eocene foraminiferal tests less commonly contain borings and endobiontic foraminifers than those from the Maastrichtian. The Eocene borings were formed in a shallower carbonate setting.