Plankton Stratigraphy and Some Remarks on Globorotalia Evolutionary Trends from the Plio-Pleistocene Sections of Southwestern Peloponnesus, Greece

Abstract

The Pliocene-Pleistocene boundary of the Androussa section is indicated by the last occurrence of Discoaster brouweri and D. triradiatus, the presence of Calcidiscus macintyrei, and the first appearance of Gephyrocapsa caribbeanica (NN19a). Hyalinea balthica is an important index fossil in the lower Pleistocene deposits of the Elea section where it appears together with Gephyrocapsa oceanica and other small Gephyrocapsa spp. (NN19b). A transitional form between the upper Pliocene foraminifera species Globorotalia bononiensis and G. inflata is recognized based on statistical analysis of apertural development. In this transitional form, apertural length is a reliable indicator of evolutionary closeness to G. inflata rather than G. bononiensis. INTRODUCTION The stratigraphical distribution of Plio-Pleistocene deposits in the Peloponnesus has previously been investigated using calcareous nannofossils (Frydas 1987, 1989b, 1990, 1993), and the nannoplankton biozones have been correlated with the biozonation of planktic foraminifera. The northwestern and western Peloponnesus is mainly dominated by lagoonal to lacustrine deposits. Marine sediments are rare in this area and when present are normally faulted (Hagemann 1979; Frydas 1987, fig. 2). The fossil nannoplankton assemblages from the NW-Peloponnesus sections have been assigned to Piacenzian age, in the interval of NN16 to NN18 biozones (Frydas 1987, 1989b). Marine deposits occupy extensive areas in the southwestern Peloponnesus, where continuous sedimentation from the lower Pliocene biozone NN13 to the lower Pleistocene biozone NN19b has been observed (Frydas 1990). In the southeastern Pelopponesus, lower Pleistocene marine deposits near the coast have been placed in biozones NN19a and NN19b (Frydas 1993). The sedimentology and the tectonic development of southwestern Peloponnesus have been studied by Kontopoulos (1978) and Zelilidis (1989). According to them the following principal lithofacies can be distinguished from younger to older: Reddish terrestrial conglomerate and sandy gravels; Mainly yellowish lagoonal fossiliferous sands and barren delta front sands alternating with sandy silts; Grayish silt and sandy silt fossiliferous lithofacies. These strata were deformed in half grabens that opened during back-arc extension of the Hellenic trench (Zelilidis and Doutsos 1992). In this work both the nannoplankton assemblages from standard sections and index planktic foraminifera species have been evaluated. In particular, the evolutionary trends of Globorotalia bononiensis and Globorotalia inflata were investigated. Emphasis was given to the stratigraphical distribution of the planktic foraminifera species and the transitional form between them. A morphometric study which follows the biostratigraphical analysis demonstrates clearly the evolutionary trend from G. bononiensis towards G. inflata. The extensive literature on the geology and stratigraphy of the Neogene of Peloponnesus, in which the paleontology is mainly concerned with macrofossils, has been previously discussed by Frydas (1987 to 1993). Correlation of the Peloponnesus Neogene TEXT-FIGURE 1 Location of studied sections in the Peloponnesus. 1: Kastro(Patras); 2, 3: Vrachneika; 4: Aghia Marina; 5: Simisa; 6: Kyllini; 7: Kyllini(camping); 8, 9: Koroni-road(a,b); 10: Rizomylos; 11: Avramion; 12: Androussa; 13: Spitali; 14: Thouria; 15: Stenossia; 16: Kremmidia; 17: Polylofos; 18: Kalamata; 19: Kokkinia; 20, 21: Elea; 22: Neapolis. micropaleontology, vol. 40, no. 4, pp. 322-336, text-figures 1-9, plates 1-2, tables 1-4, appendix 1, 1994 322 This content downloaded from 207.46.13.139 on Thu, 27 Apr 2017 17:50:27 UTC All use subject to http://about.jstor.org/terms Micropaleontology, vol. 40, no. 4, 1994 TEXT-FIGURE 2 TEXT-FIGURE 3 Location of Rizomylos section. Location of Androussa section. to the biostratigraphic zonal scheme developed for the eastern Mediterranean by Ellis and Lohman (1979, DSDP Leg 42A) is discussed elsewhere (Bellas and Frydas, in press). In addition, a number of the most important Pliocene-Early Pleistocene sequences in different areas of the northern Mediterranean basin, especially in Italy, were discussed by Ioakim et al. (1990). The aim of the present paper is the investigation of the Pliocene/Pleistocene boundary in the southern Peloponnesus (text-fig. 7).