Microfauna and sedimentary-tectonic history of the Oligo-Miocene of the Ionian Islands and Western Epirus (Greece)

Abstract

Detailed lithostratigraphic and biostratigraphic investigations were carried out in Oligocene-Miocene sediments on the Ionian islands Ithaki, Levkas, Kerkira and Kefallinia and in the western part of Epirus (Greece). Zonations based on planktonic organisms and on the foraminiferal families Miogypsinidae and Lepidocyclinidae are applied to unravel the complex sedimentary and tectonic history of this part of the eastern Mediterranean. In spite of several inaccuracy factors, a tentative correlation was established of the larger and planktonic foraminiferal zones with the international chronostratigraphic scale. The detrital sedimentation was strongly controlled by tectonics, which have caused more intense deformation of the Oligocene-Early Miocene on the islands of Ithaki, Levkas and Kefallinia, than of contemporaneous deposits on Kerkira and in western Epirus. These tectonics are considered to fit best in a tensional stress pattern, causing horst and graben structures, vertical block movements and strike-slip displacements along old, deepseated fracture systems. In Middle Miocene time, thrust-faulting, most active in the west, seems to have variously affected the area. The phylogenetic development of the Miogypsina assemblages in NW Greece seems to confirm the evolutionary trends known from other areas in the Mediterranean. The absence of retardation in the successive Greek Miogypsinoides assemblages might suggest another bioprovince than nearby Sicily or Egypt, during the Burdigalian. A classification of the European Nephrolepidina lineage, consisting of the successive species praemarginata-morgani-toumoueri, based on biometric criteria of assemblages, is proposed.