Plankton biostratigraphy and paleoclimatic implications of an early late miocene sequence of Levkas island, Ionian Sea, Greece (original) (raw)
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Bulletin of the Geological Society of Greece
The Manassi section in Levkas Island belongs to the Pre-Apulian (Paxos) zone, the most external domain of the Hellenic realm. Its Early Tortonian sediments contain a rich foraminiferal fauna dominated, in numbers of individuals, by planktic species. Its benthic foraminiferal assemblage is characterized by a high number of taxa, with low numbers of individuals. Their study provides a basis for interpreting the paleobathymetry of the basin.The Manassi section represents deposition in upper to lower bathyal depths, during a period of intense tectonic activity. Downslope transport of fauna by turbidity currents partly overprints the signal of paleobathymetrically-diagnostic foraminifera distribution. The recognition of allochthonous taxa is used, together with %P, to identify turbidite beds intercalated with in-situ marly sediments. The micropaleontological and paleobathymetrical analyses of the studied sediments indicate that these correspond to distal atypical flysch deposited in the ...
Geobios, 2008
Based on calcareous nannofossils and planktonic foraminifera1 biostratigraphic data from flysch sequences, we give evidence for the paleoenvironmental evolution of Gavrovo and Ionian foreland basins (External Hellenides, Etoloakarnania region). Our data suggest that the onset of clastic sedimentation in both foreland basins in the study area is chronostratigraphically placed at Late Eocene (from 36.2-34.4 Ma; nannofossil biozones NP19-20, planktonic foraminifera biozones P16-17). During the earliest Oligocene (NP21-22 nannofossil biozones/34.4-32.45 Ma), both basins represent restricted accumulation of sediments, mainly composed of clays and silts. The presence of thick flysch deposits, accumulated during Early Oligocene (33.4-30 Ma, nannofossil zone NP23), indicates an increasing rate of sediment supply. The flysch sequences in the Ionian basin are associated with a distal depositional environment, while in the same time the sedimentation in the external part of Gavrovo basin is related to a more proximal environment that is gradually deepening. On the contrary, the internal part of Gavrovo basin is characterised by deep-water facies, deposited in the Early Oligocene. At the end of Early Oligocene and the onset of Late Oligocene (nannofossil zone NP24/30-27.2 Ma, planktonic foraminifera zone P21), the deposition of coarse grained sediments in both basins indicates a shift to shallower depositional environment. The accumulation of fine-grained sediments during Late Oligocene (27.2-23.2 Ma, NP25 nannofossil biozone) in the Ionian basin marks the youngest flysch sediments in the Etoloakarnania region and specifies the time of the Gavrovo nappe emplacement on the Ionian zone. Moreover the emplacement of Pindos nappe on the Gavrovo zone is estimated between 30-27.2 Ma (NP24 biozone) as supported by the nannofossil analysis of samples in front of Pindos thrust.
The Messinian pre-evaporitic sedimentary succession of Gavdos island (Metochia section) is a nearly uninterrupted succession of marine sediments, dominated by finely laminated diatomaceous sediments, which are cyclically alternating with marlstone and white limestone beds. The purpose of this study is to analyze in detail the benthic and planktonic foraminiferal microfauna preserved in the sediments of this section. The qualitative and quantitative analysis of the planktonic foraminifera fauna allowed the recognition of seven bioevents, which have been astronomically dated for the Mediterranean. The base of the diatomitic succession in Gavdos Island is dated at 6.696 Myr, whereas its top at 6.0 Myr. Our results suggest that two environmental parameters are the most important factors that control the community structure of the benthic foraminiferal fauna: the food availability and oxygen concentration. In addition, local upwelling phenomena evidenced by signals from the benthic foraminifera and the distribution pattern of the planktonic G. bulloides may have played a role in the faunal density and composition.
Paleoceanography, 1998
To reconstruct paleoceanographic changes in the eastern Mediterranean during the last 330,000 years, we studied benthic foraminifera in a piston core from the Ionian Sea. The fauna exhibits large fluctuations in foraminiferal number, diversity, and species composition. Interglacials are characterized by low foraminiferal number and diversity indicating oligotrophic conditions. Directly below or above interglacial sapropels, increased numbers of low-oxygentolerant species indicate a strong reduction of deep water circulation. Glacials are characterized by increased foraminiferal number and diversity and faunas that are dominated by shallow infaunal species indicating mesotrophic conditions. Around glacial sapropel S6 very high foraminiferal numbers and the dominance of shallow and deep infaunal species suggest enhanced organic matter fluxes. These faunal results provide information about changes in the African and North Atlantic climate systems (monsoon and westerlies) controlling the humidity and wind stress in the Mediterranean region. 1981; Sperling, 1996]. Although the abundance and species composition of benthic foraminifera in the eastern Mediterranean underwent significant temporal changes in the late Quaternary which reflect past environmental conditions, only a few paleoecological and paleoceanographic studies have been carried out [e.g., Mullineaux and Lohman, 1981; Parisi and Cita, 1982; Vismara Schilling, 1986; Oggioni and Zandini, 1987; Nolet and distribution patterns and microhabitats of Recent benthic Corliss, 1990]. These studies have shown that distinct benthic foraminifera in the Mediterranean are mainly controlled by the foraminiferai faunai changes were aSSOciated •ith depogition of the organic-rich sapropel layers that regularly occur in Neogene Copyright 1998 by the American Geophysical Union Mediterranean sediments. In general, nonsapropel assemblages are characterized by faunas rich in miliolid taxa, whereas faunas Paper number 98PA01864. adjacent to or within sapropels are dominated by deep infaunal 0883-8305/98/98PA-01864512.00 and low-oxygen-tolerant genera, like Globobulimina, 447 448 SCHMIEDL ET AL.: BENTHIC FORAMINIFERA IN THE IONIAN SEA Chilostomella, Bolivina and Fursenkoina [Mullineaux and Lohman. 1981; Katz and Thunell, 1984; Ross and Kennett, 1984; Nolet and Corliss . 1990]. On the basis of a number of palynological and geochemical studies it has been shown that the late Quaternary climate of the Mediterranean region is generally characterized by humid interglacials accompanied by low b180 values and arid glacials defined by high b180 values [e.g., Mommersteeg et al., 1995; Cheddadi and Rossignol-Strick, 1995; Zonneveld, 1996]. One of the main sedimentological characteristics of the eastern Mediterranean is the cyclic deposition of sapropels that point to drastic changes in the marine environment. Previous studies on the origin of these anoxic events discussed both severe decreases in the ventilation of subsurface waters [Rossignol-Strick et al., 1982; Fontugne et al., 1989; Thunell and Williams, 1989; Bethoux, 1993; Tang and Stott, 1993] and increased paleoproductivity followed by high organic carbon flux rates to the seafloor [Castradori, 1993; Sancetta, 1994]. One striking result is that the formation of sapropels is closely associated with changes in humidity related to precessional forcing of the African monsoon system [Rossignol-Strick et al., 1982; Rossignol-Strick, 1985; Kutzbach and Street-Perrot, 1985; Prell and Kutzbach, 1987; 136/27, 1-3 of the Deutsche Forschungsgemeinschaft (DFG). W. Hieke, chief scientist of cruise Meteor 25/4 (August 1993), F. Werner, and W. Rehder are cordially thanked for their support for the piston coring program. Our thanks are extended to the entire shipboard party and crew for their invaluable help. We are grateful to I. Breitinger, who helped to sample and to prepare the data set, and S. Flaiz and D. Mahlen, who skillfully carried out laboratory preparations. We are indebted to J. Pross for helpful discussions and critical reading of an earlier version of the manuscript. The critical reviews of F. Jorissen and two anonymous reviewers and the editorial work of M.L. Delaney and an associate editor
The present study describes the early late Miocene paleoenvironmental evolution and the main paleoclimatic trends of Gavdos Island (eastern Mediterranean) reconstructed using planktonic foraminifera. The three stratigraphic sections studied in this area are characterized by whitish to greyish marls and sands (Potamos and Ag. Giannis sections) and by grey-bluish marls and reefal limestones (Bo Section). Based on the distributional pattern of neogloboquadrinids in the three sections, we attribute a lower Tortonian age to studied sediments, corresponding to the interval ranging between 11.21 to 10.01 Ma. Four distinct assemblages of planktonic foraminifera were identifi ed by Q-mode cluster analysis. The succession of assemblages allows dividing each section into four paleoceanographic stages: 1) a warm-oligotrophic stage characterized by the prevalence of Globigerinoides obliquus-Globoturborotalita apertura; 2) a cool eutrophic stage characterized by Neogloboquadrina acostaensis; 3) upwelling conditions dominated by Globigerina bulloides; and 4) a relatively warm with seasonal high productivity stage characterized by the N. acostaensis and Globigerinoides trilobus. On the basis of planktonic foraminifera paleoclimatic indices, paleoclimatic curves were constructed for each section. Our data suggest that, although adjacent, the areas where the three sections are located underwent different paleoclimatic and paleoenvironmental evolution during early late Miocene: Bo shelf is characterized by warmer, nearly oligotrophic conditions compared to cooler and eutrophic conditions on the adjacent Potamos and Ag. Giannis shelves. Th is diff erence is probably related to the presence of an island between Bo shelf and the open sea which acted as a local oceanographic and biogeographic barrier.
CFS Courier Forschungsinstitut Senckenberg
Oligocene and Early Miocene sedimentary successions are studied in the Mesohellenic Basin of northwestern Greece. Two sections covering the base and the top of the basin infill were measured in detail in the northern part of the basin. They mainly consist of fine grained siliciclastic sediments and minor carbonates with few intercalated highly fossiliferous horizons. Five different palaeoenvironments are recognised in the Oligocene deposits of the Mesolouri/Doutsiko section: (I) coral reef and inter-reef, (2) fore-reef, (3) basinal settings with faunal mixing, (4) basinal deep-water, and (5) shallow marine/sublittoral environments. The fauna is dominated by molluscs and smaller foraminifers, corals and larger foraminifers are locally abundant. Echinoids and calcareous red algae are infrequent. A large reef structure ("Petra Reef') situated directly on top of the ophiolithic basement with a highly diverse Early Oligocene coral assemblage occurs at the very base of the Mesolouri/Doutsiko section. Well preserved and diverse gastropod and bivalve associations as well as smaller benthic foraminifera are used for palaeoecological reconstructions. The mixed occurrence of shallow water organisms and foraminifers which are generally regarded as deep-water forms, in the basal part of the Mesolouri section, is discussed. The molluscs mainly occurred in deeper sublittoral and in shallow sub littoral to littoral palaeoenvironments where they are partly associated with corals. A widely distributed Acropora-Iayer represents one of the first known coral assemblages dominated by Acropora in the Cenozoic.
The South Evoikos Basin is a marginal basin in the Aegean Sea which receives little terrigenous supply and its sedimentation is dominated by hemipelagic processes. Late Quaternary benthic and planktonic foraminifera from core PAG-155 are investigated in order to understand their response to the glacial-interglacial cycles in this region. The quantitative analysis of planktonic foraminifera, coupled with accelerator mass spectrometry (14 C-AMS) radiocarbon date measurements, provide an integrated chrono-stratigraphic time framework over the last 90 ka (time interval between late Marine Isotopic Stages 5 and 1; MIS5-MIS1). The temporary appearance and disappearance as well as several abundance peaks in the quantitative distribution of selected climate-sensitive planktonic species allowed the identification of several eco-bioevents, useful to accurately mark the boundaries of the eco-biozones widely recognized in the Mediterranean records and used for large-scale correlations. The established bio-ecozonation scheme allows a detailed palaecological reconstruction for the late Pleistocene archive in the central Aegean, and furthermore provides a notable contribution for palaeoclimatic studies, facilitating intercorrelations between various oceanographic basins. The quantitative analyses of benthic foraminifera identify four distinct assemblages, namely Biofacies: Elphidium spp., Haynesina spp. Biofacies, characterized by neritic species, dominated during the transition from MIS 5 to MIS 4; Cassidulina laevigata/carinata Biofacies dominated till 42 ka (transgressive trend from MIS 4 to MIS 3); Bulimina gibba Biofacies dominated from 42 ka to 9.5 ka (extensive regression MIS 3,2 through lowstand and early transgression; beginning of MIS 1); Bulimina marginata, Uvigerina spp. Biofacies dominated from 9.5 ka to the present (late transgression through early highstand; MIS 1)., This study showed that the South Evoikos Basin which is characterized by its critical depths and connections to the open sea, and its small volume water masses that nourished foraminiferal assemblages, accurately records 5th À 4th order sea level and climatic fluctuations. Especially , the basin's limited communication with the open ocean implies that any climatic signals will be recorded in an amplified fashion, and therefore this heightened sensitivity to the effects of climate variability further underlies the prominent role of such marginal basins in the understanding of the global climatic evolution.