Original paper

Nannoplankton-Biostratigraphie der tertiären Mesohellenischen Molasse (Nordwest-Griechenland)

[Nannoplankton Biostratigraphy of the Tertiary Mesohellenic Molasse (Northwest Greece)]

Zygojannis, Nikolaus; Müller, Carla

Kurzfassung

Untersuchungen des kalkigen Nannoplanktons in den tertiären Molasse-Serien des Mesohellenischen Trogs (NW-Griechenland) ermöglichen die biostratigraphische Einstufung der dort akkumulierten Sedimente in die Nannoplankton-Zonen NP 18-NP 19/20 (Obereozän), NP 23-NP 25 (Mittel-Oberoligozän) und in die Zonen NP 2-NP 4 (Untermiozän). Es ergaben sich dabei z.T. Abweichungen von den bisherigen Altersbestimmungen, die auf Mollusken und Foraminiferen beruhen. Stratigraphische Lücken (möglicherweise NP 20 bis untere NP 23 = oberstes Obereozän bis unterstes Mitteloligozän) sowie im untersten Miozän (Aquitan, NN 1) können auf orogenetische Vorgänge zurückgeführt werden.

Abstract

A scheme of the evolution of the Mesohellenic Basin (Northwest-Greece) is proposed from results obtained by geological and paleontological investigations of this area. Age determinations are based on calcareous nannoplankton which gives partially different results than those obtained by molluscs and foraminifera. Two different regions can be recognized in the Mesohellenic Basin. The northern part is characterized by thick sequences deposited in a deeper fast subsiding basin, whereas in the southern part a shallow basin with reduced sequences existed. Shallow water limestone of middle Eocene age (dated by foraminifera, BIZON et al. 1968, SOUMAN & ZYGOJANNIS 1977 a, 1980) is transgressive upon older basement rocks.The limestone is overlain by a clastic sequence of upper Eocene to lower Miocene rocks (nannoplankton zones NP 18 to NN 4). An unconformity which represents the lower Oligocene and may be a part of the uppermost Eocene can be correlated with tectonic events. The postorogen Molasse sedimentation begins within the middle Oligocene (nannoplankton zones NP 23-NP 24). The sediments are rich in nannoplankton. Also reworked Cretaceous and Eocene species are frequent. The middle Oligocene (Pentalofon serie) is overlain by the upper Oligocene (nannoplankton zone NP 25) Tsotilion serie. The upper part of this serie belongs already to the lower Miocene (Burdigalian, nannoplankton zones NN 2-NN 4). It was not possible to date the lowermost part of the Miocene (Aquitanian, nannoplankton zone NN 1). A hiatus might correspond to this interval. In the marginal southern parts of the Mesohellenic Basin this hiatus corresponds to a longer period of time, either due to non deposition or erosion.

Keywords

Sectionmolassebiostratigraphy (nannoplankton zones)nannoplankton. Upper EoceneMiddle OligoceneUpper OligoceneLower Miocenegappyrenean orogenysubsiding basintardigeosynclinesedimentary rate EpirusGreek Macedonia