Biostratigraphic analysis of Paleogene lowstand wedge conglomerates of a tectonically active platform margin (Zakynthos Island, Greece)

Abstract

Paleogene heterometric and polymictic conglomerate deposits were investigated in Zakynthos Island (Ionian Islands, Greece) from different outcrops, along the eastern flank of the anticline crossing the island in a NNW-SSE direction. This structure is formed by the Meso-Cenozoic sedimentary succession of the Pre-Apulian zone. The Paleogene facies sequence of Zakynthos consists of toe of slope accumulations of mainly resedimented material produced by gravity flows during repeated falls of relative sea-level below the shelf edge, with subsequent erosion of the exposed Cretaceous-Paleogene sequences. The lithoclasts are scattered within different sedimentary wedges of coarse detrital material; their study provided information on the stratigraphy and depositional environments of the eroded Cretaceous-Paleogene succession. The fossil assemblage content of the conglomerate clasts is interpreted in the frame of a carbonate ramp model. The lack, elsewhere in the island, of in situ sequences corresponding in age and facies to the sampled lithoclasts and the occurrence of different sedimentary facies sequences suggest a differential tectono-sedimentary evolution of the depositional substratum during the Late Cretaceous and the Paleogene. Considering the eastward transition to the Ionian basin, an eastern source of the clasts can be excluded, whereas in Cephalonia Island in the Lixouri peninsula a stratigraphic record with characters similar to those of the Zakynthos conglomerate clasts has been documented. The systematic investigation of the well-preserved Paleogene larger foraminiferal assemblages led to the recognition of 42 different taxa (34 of specific rank). Several taxa are rare in coeval deposits from the Mediterranean Tethys and some are as yet undescribed. A comparison with coeval assemblages from the Mediterranean Tethys is attempted, in order to outline stratigraphic and biogeographic relationships.