Benthic foraminiferal distribution and tectonic significance of the early Late Miocene tectonostratigraphic deposits of the Pre-Apulian zone, western Greece. Benthic foraminiferal distribution and tectonic significance of the early Late Miocene tectonostratigraphic deposits of the Pre-Apulian zone, western Greece. Hara DRINIA & Assimina ANTONARAKOU National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment, Panepistimiopolis 157 84, Athens GREECE Ionian Islands in western Greece represent o They 1 . ne of the most tectonically active regions of the Eastern Mediterranean. constitute part of the para-autochthonous Apulian foreland of the Hellenide orogen and include rocks of the Pre-Apulian (or Paxos) and Ionian isopic zones (Aubouin 1957, 1965; Underhill 1989). In Levkas Island, the Pre-Apulian zone is represented in Agios Petros area which covers the southwestern part of the island and is separated from the Ionian limestones by a major NE-SW oriented thrust fault, known as the Kalamitsi Thrust (Fig. ). The Manassi section, which is proximal to the thrust fault, is located on the eastern slope of a N-S running valley, near the village of Manassi The studied succession consists of blue grey marls and clays with some fine grained sandstone interbeds. The intercalations of these thin, clastic beds and especially of positively graded sandstones in the studied succession reflect the influence of density currents, which supplied coarser material from a distant hinterland (de Mulder, 1975). The Manassi section is the only section in the vicinity of the thrust fault that is fully exposed in outcrop, where closely packed stratigraphic samples can be undertaken. INTRODUCTION 50 km Ionian islands Alluvial deposits Scree deposits Ionian Zone Pre-Apulian or Paxos Zone Molasse Fault Kalamitsi Thrust 5 km Manassi 391-1 391-2 391-3 391-4 391-5 391-6 391-7 391-8 391-9 391-10 391-11 391-12 391-13 391-14 391-15 391-16 391-17 391-18 391-19 391-20 391-21 391-22 391-23 391-24 391-25 391-26 5m Marls Silty marls Sand MANASSI SECTION METHODS The benthic foraminiferal dataset consisting of raw counts of 167 species was computerized for analysis and standardized by converting counts to proportions of sample totals. Based on the faunal counts, Benthic Foraminiferal Numbers (BFN; number of specimens per gram dry sediment) were calculated. The percentage of planktic species in the total foraminiferal association (%P) was calculated, in order to reconstruct paleodepth and track sea-level changes. . Biodiversity is quantified using the Information Function – Shannon-Wiener index Paleobathymetry in m was calculated for each sample by introducing P/B ratios based on “normal” open marine taxa, disregarding stress marker species in the equation of van der Zwaan et al. (1990) The purpose of this is to establish the magnitude of paleoenvironmental and paleobathymetric changes throughout the Early Tortonian part of the pre-Apulian zone from Levkas island. For this reason, we undertake benthic foraminiferal analysis of a closely packed suite of samples to establish paleobathymetry changes through the succession, in order to (1) estimate the water depth (paleobathymetry) in which the sediments were deposited, and to (2) assess the benthic foraminiferal setting in which deposition took place. The paleobathymetric evolution of the studied sediments together with the faunal pattern provide the key to unlocking the broader question as to whether the depositional pattern within this part of the Agios Petros Basin was driven by tectonic or eustatic change. work benthic foraminiferal will SCOPE 0 50000 BFN 0 50 100 P/P+B% 0 400 800 1200 Paleodepth (m) 0 2 4 Shannon H(s) index 391-1 391-2 391-3 391-4 391-5 391-6 391-7 391-8 391-9 391-10 391-11 391-12 391-13 391-14 391-15 391-16 391-17 391-18 391-19 391-20 391-21 391-22 391-23 391-24 391-25 391-26 T Benthic Foraminiferal Number ( ) . he distribution patterns of the dominant and associated species ( and ), together with the decreased BFN values, elevated diversities and higher planktic-to-benthic ratios, suggest deposition at bathyal water depths with moderate organic matter fluxes and elevated oxygen contents of the bottom water, typical for this water depth interval S. reticulata C. kullenbergi 391-1 391-2 391-3 391-4 391-5 391-6 391-7 391-8 391-9 391-10 391-11 391-12 391-13 391-14 391-15 391-16 391-17 391-18 391-19 391-20 391-21 391-22 391-23 391-24 391-25 391-26 0 400 800 1200 Paleodepth (m) Sedimentary gap Significant uplift due to regional compression Relative long period of tectonic quiescence Rapid subsidence Minor amplitude, short duration uplift, due to local reorientation of stress-field. High amplitude fluctuations of the water depth was probably caused by fluxes of sediment from shallower parts of the basin The tentative sea-level curve does not correspond to the global sea-level curve suggesting that external/ allocyclic or internal/autocyclic factors may have affected sedimentation. Comparison between the paleodepth curve and the isotope record of Zachos et al. (2001) shows opposite trends for the two curves throughout the investigated interval, reflecting that an increased tectonic activity affected sedimetation. Flexural loading is inferred to have resulted in regional tectonic subsidence and consequently in relative sea- level rise. CONCLUSIONS - SUBSIDENCE HISTORY CONCLUSIONS - SUBSIDENCE HISTORY RESULTS Ser4/Tor1 Long-term and short term eustatic curves Haq et al. (1987) Hardenbol et al. (1998) Deep-sea Zachos et al. (2001) δ18 Ο 5 4 3 2 1 0 200 0 0 10 20 TB3 TB2 TB1 According to Antonarakou (in press), t t dated in Mediterranean at 11.4 Ma by Turco et al. (2001). he biostratigraphic analysis based on planktonic foraminifera indicates that he studied sequence has been deposited just above the global sequence boundary Ser4/Tor1, dated at 11.7 Ma, which represents a low sea-level event, corresponding to MSi-4 oxygen cooling event of Abreu & Anderson, (1998) which is time equivalent to Mi5 cooling event of Miller et al. (1991), REFERENCES Abreu, V.S. & Anderson, J.B., 1998. Glacial eustasy during the Cenozoic: sequence stratigraphic implications, AAPG Bull. 82 (7), 1385-1400. Aubouin, J., 1957. Essai de correlation stratigraphique de la Grece occidentale. Bulletin de la Societe Geologique de France, 7, 281-304. Aubouin, J., 1965. Geosyclines. Developments in Geotectonics; Elsevier, Amsterdam. De Mulder, E.F.J., 1975. Microfauna and sedimentary-tectonic history of the Oligo-Miocene of the Ionian Islands and Western Epirus (Greece). Utrecht Micropaleont. Bull. 13, 1-139. Haq, B.U., Hardenbol, J. & Vail, P.R., 1987. Chronology of fluctuating sea levels since the Triassic. Science 235, 1156-67. Hardenbol, J., Thierry, J., Farley, M.B., et al., 1998. Mesozoic and Cenozoic sequence chronostratigraphic framework of European basins. In P.-C. de Graciansky, J. Hardenbol, T. Jacquin and P.R. Vail (eds). Mesozoic-Cenozoic Sequence Stratigraphy of European Basins, Society of Economic Paleontologista and Mineralogists Special Publication, vol. 60. Tulsa OK: SEPM, 3-13, 763-781. Miller, K.G., Wright, J.D. & Fairbanks, R.G., 1991. Unlocking the icehouse: Oligocene-Miocene oxygen isotope, eustasy, and margin erosion. J. Geophys. Res. 96, 6829- 6848. Turco, E., Hilgen, F.J., Lourens L.J., Shakleton, N.J. & Zachariasse, W.J., 2001. Punctuated evolution of global climate cooling during the late Middle to early Late Miocene: High-resolution planktonic foraminifera and oxygen isotope records from the Mediterranean. Paleoceanography, 16, 405-423. Underhill, J.R., 1989. Late Cenozoic deformation of the Hellenic foreland, Western Greece. Bull. Geol. Soc. Am. 101, 613-634. Van der Zwaan, G.J., Jorissen, F.J. & De Stigter, H.C., 1990. The depth dependency of planktic/benthonic foraminiferal ratios: constraints and applications. Mar. Geology, 95, 1-16. Zachos, J., Pagani, M., Sloan, L., Thomas, E. & Billups, K., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science, 292, 686-93.