Open Journal of Geology, 2014, 4, 59-68 Published Online March 2014 in SciRes. http://www.scirp.org/journal/ojg http://dx.doi.org/10.4236/ojg.2014.43006 How to cite this paper: Lykoudi, E.E. (2014) New Data on the Upper Miocene Presence in the Aegean Region: The Geologi- cal Evolution of Spetses Island, Peloponnesus, Greece. Open Journal of Geology, 4, 59-68. http://dx.doi.org/10.4236/ojg.2014.43006 New Data on the Upper Miocene Presence in the Aegean Region: The Geological Evolution of Spetses Island, Peloponnesus, Greece Evdoxia E. Lykoudi Department of Geological Sciences, School of Mining Engineering and Metallurgy, National Technical University of Athens, Athens, Greece Email: elykoudi@metal.ntua.gr Received 27 January 2014; revised 23 February 2014; accepted 2 March 2014 Copyright © 2014 by author and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract Based on detailed geological and geomorphological mapping, sampling and micro-palaeontologi- cal determinations, both of the alpine and neogene formations, new data have been derived for Spetses Island (SW Aegean). The applied methodology provided results on the paleogeographic evolution for Spetses Island and the nearby land of Argolida peninsula as well. Based mainly on characteristic nannofossils, a Miocene age of the post-alpine formations is determined. It is the first time that miocene formations have been identified, not only in Spetses Island and Argolida, but in the whole area of Peloponnesus, where only Plio-pleistocene deposits have been described. This work also leads to the conclusion that Spetses Island is attached to the Argolida peninsula, forming an independent paleogeographic unit since Upper Miocene. Keywords Upper Miocene; Microfauna; Spetses Island; Aegean Region 1. Introduction The island of Spetses is located near the south-western coast of the Argolida peninsula, in central Peloponnesus (Figure 1). Until today, the geological structure and the paleogeographic evolution of the island are unknown to a large extent. Some information was provided by the geological map of Greece in scale 1:500,000, where the Neo- gene formations were referred to as of plio-pleistocene age [1], while other authors also reported the presence of plio-pleistocene sediments on the island of Spetses [2] [3]. This geological, geomorphological and stratigraphi- cal work resulted in the compilation of the geological map of the island and the identification of the factors that