Metochia Section Research Articles

Stress precursors of the Messinian salinity crisis as recorded by calcareous plankton and geochemistry in the Eastern Mediterranean: The Upper Metochia section of the Gavdos Island (Greece)

The road to the Messinian salinity crisis was paved with increasing environmental stress in the Mediterranean marine realm. The nature and origin of the crisis of the marine biota is still matter of debate because the crisis itself hinders univocal paleoenvironmental reconstructions by selecting the most resilient taxa, which are generally adapted to a wide range of stresses. The commonly accepted hypothesis, recently reiterated, is that increasing salinity was the main factor eliminating the marine biota from the geological record and eventually leading to the deposition of evaporitic carbonates in the Eastern Mediterranean just before the onset of the crisis dated at 5.97 Ma. We suggest that stratification and increasing restriction (continental water influence), leading to strong variability of surface water conditions, better explain the 87Sr/86Sr excursion below the global ocean value and the pattern of calcareous plankton events in the uppermost portion of the Metochia section (Gavdos Island, Greece), from 6.24 to 5.95 Ma. The early reduction of foraminifera at 6.07 Ma, typical of relatively deep successions lacking primary gypsum during the first phase of the crisis, precedes a sequence of calcareous nannofossil events such as the influx of Braarudosphaera bigelowi at 6.168 Ma, the acme of Reticulofenestra perplexa at 6.058–6.018 Ma, and the peaks of Sphenolitus spp. and Helicosphaera carteri at 5.99 and 5.973 Ma, respectively. The peak of such opportunistic calcareous nannofossil and the foraminifer disappearance, commonly observed in both deep and shelf successions, closely approximate the onset of the Messinian salinity crisis, regardless the occurrence of the Primary Lower Gypsum unit, and is interpreted as the final restriction step, which led to a 600 ky environmental perturbation culminating with the deposition of the Mediterranean salt giant.

The Messinian of Agios Myron (Crete, Greece): A key to better understanding of diatomite formation on Gavdos (south of Crete)

The Agios Myron section in the NE of the Heraklion Basin on central Crete exposes a pre-evaporitic Messinian sequence of 24 sedimentary cycles of deep-marine homogeneous and laminated marls (sapropels). Planktonic foraminiferal biostratigraphy and ash layers show that the 24 cycles in section Agios Myron correlate to cycles M79 to M102 in the well-studied and orbitally tuned Metochia section on Gavdos Island. The correlation of the cycle patterns in sections Agios Myron and Metochia not only provides tuned ages for sedimentary cycles, planktonic foraminiferal bioevents, and ash layers in Agios Myron, but also reveals that the diatomites in Metochia cycles M94-M102 have no equivalents at Agios Myron. The onset of diatomite formation on Gavdos at 6.72 Ma is shown to coincide with eutrophication and related to a restriction-imposed increase in salinity 20 kyr earlier at 6.74 Ma. Geographic differences in productivity and possibly also the better preservation potential of siliceous microfossils on the much deeper seafloor at the Metochia site are believed to explain why diatomites are present on Gavdos and absent in time-equivalent levels at Agios Myron.

FORAMINIFERAL RECORD OF ENVIRONMENTAL CHANGES: PREEVAPORITIC DIATOMACEOUS SEDIMENTS FROM GAVDOS ISLAND, SOUTHERN GREECE.

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

Source rock potential of the Late Miocene Metochia formation of Gavdos Island, Greece

Rock-Eval method was used to analyze 53 samples from late Miocene Metochia Formation of Gavdos Island (south of Crete Island) in order to characterize the contained organic matter and to evaluate its potential as source rock. The samples were collected from Metochia Section which consists of about 100 m thick marlssapropels alternations. Organic matter analysis showed that the studied succession could be subdivided into two parts. The lower one, which is generally rich in organic matter and the upper one, which is poor. In the lower part the rich horizons in organic matter are characterized by Kerogen type II, III and IV, with low oxygen content, and with fair to very good potential for gas and/or oil hydrocarbon generation. Additionally, the studied samples are thermally immature. Taking into account that the studied area has never been buried in such a depth to reach conditions of maturation, as well as, that the studied section in Gavdos is connected with Messara basin located in the northeastern and, finally, that the main part of Gavdos basin, which is situated between Gavdos and Crete islands, has continuously encountered subsidence, we could conclude that sediments of Metochia Formation could act as source rocks but in the more deep central part of the Gavdos basin.

Tracking provenance change during the late Miocene in the eastern Mediterranean using geochemical and environmental magnetic parameters

Marls of the Metochia section (Gavdos, Greece) have been analyzed using geochemistry, environmental magnetism, and diffuse reflectance spectrometry to study late Miocene paleoenvironmental changes in the eastern Mediterranean region. Fuzzy c‐means cluster analysis (FCM), combined with nonlinear mapping (NLM), has been performed on a multiparameter data set to identify and characterize terrigenous source areas from North Africa and the Aegean margin. The parameters included in the FCM were selected on the basis of their univariate characteristics and their ability to trace input changes from regional source areas. The hard isothermal remanent magnetization (HIRM), calculated on a carbonate‐free basis, and the Ti/Al ratio are used to distinguish aeolian dust and transport mechanisms of material originating from North Africa. Mass accumulation rates of Al and Ni are employed to represent the input of terrigenous material originating from the Aegean region. CaCO3, calculated from Ca abundance, provides information concerning marine productivity and Mn/Al is used to trace reductive diagenesis in the marls. After performing the FCM and NLM analysis, a four‐cluster solution has the greatest stability and describes paleoenvironmental changes in both the African and European source areas. The cluster solution clearly reveals the change from input dominated by terrigenous material in the lower parts of the Metochia section to marine input at the top of the section but also reveals changes in paleoenvironmental conditions in North Africa from arid to more humid conditions at ∼8.2 Ma.

Palaeoenvironmental conditions preceding the Messinian Salinity Crisis: A case study from Gavdos Island

The Messinian pre-evaporitic sedimentary succession of Gavdos Island (Metochia section) is a nearly uninterrupted succession of marine sediments, dominated by finely laminated diatomaceous marls, which are cyclically alternating with clayey diatomites and white diatomites. The qualitative and quantitative analysis of the planktonic foraminiferal fauna allowed the recognition of nine bioevents, which have been astronomically dated for the Mediterranean. The base of the diatomitic succession in Gavdos Island is dated at 6.722 Ma and the top at 6.015 Ma. The studied section contains benthic foraminiferal genera characteristic of an outer shelf to slope environment. The qualitative and quantitative analysis of this microfauna revealed three benthic foraminiferal fossil assemblages and the occurrence of allochthonous species transported into the bathyal environment by current activity. The cyclical pattern of the benthic foraminifera assemblages indicates that the studied sediments have been affected by repeated episodes of basin restriction characterized by low diversity benthic foraminifera populations, and a limited planktonic foraminifer association typified by shallow, surface-dwelling forms. This restriction was partly due to Antarctic cooling, which produced palaeo-Mediterranean sea-level oscillations during the Early Messinian, as a prelude to closure of the Atlantic connections. The relative impact of climatic versus tectonic control on sedimentation patterns within this basin is discussed.

THE APPLICATION OF CYCLOSTRATIGRAPHY AND ASTROCHRONOLOGY IN THE NEOGENE MARINE DEPOSITS OF EASTERN MEDITERRANEAN: METOCHIA SECTION (GAVDOS ISLAND)

Significant lithostratigraphical and micropaleontological signatures, of Milankovitchscale climatic changes are recorded in Miocene deep-sea sediments. As a case study, the Metochia Section, in Gavdos Island, which covers the time interval from 9.7 to 6.6 Ma, is used. This study emphasizes the sedimentological and micropaleontological characteristics of the section, attributed to Milankovitch-scale climatic changes. The short-term variations in climate and faunal composition are related to precession- controlled sedimentary cycles and the long-term trend in climate is related to eccentricity and obliquity cycles. Regional changes in sea surface temperature in combination with variations of solar insolation have caused the cyclical astronomical controlled pattern of Globorotalia species.

The occurrence of Bolboforma in the Upper Miocene Metochia Section, Gavdos Island, south of Crete (Greece)

The occurrence of Bolboforma in the Upper Miocene Metochia Section, Gavdos Island, south of Crete (Greece)

Planktonic foraminiferal ecozones: response of the pelagic environment to palaeoclimatic changes in the eastern Mediterranean Sea

A detailed study of the planktonic environment of the eastern Mediterranean Sea has permitted the reconstruction of the climatic history of this part of the basin during the time span from 9.7 to 6.6 Ma. The eastern Mediterranean Sea is confirmed as having a strong sensitivity to the climatic changes that occurred during that timespan. One of the very few complete hemipelagic successions of the Upper Miocene in Mediterranean is found in Gavdos island (SW Crete). Quantitative and qualitative modifications of the planktonic foraminiferal communities observed in Metochia section exhibit a sequence of biological events summarized in 11 successive main time intervals. The bioevents are defined by frequency peaks and/or local (re)-occurrences or (temporary) disappearances of some of the taxa, in association with more or less important fluctuations of the more common species. The planktonic foraminifera show a strong correlation with sea surface temperature variations and with changes in the physical and chemical properties of the upper water column caused by the climatic instability. Two prominent shifts in faunal parameters divide the period recorded in Metochia section into three major time slices that are discussed in chronological order: a cooling trend from 9,7 to 7,6 Ma, a warmer period from 7,6 to 7,2 Ma and then a cooling trend which finishes at the Messinian.

Late Miocene calcareous nannofossil biotratigraphy and astrobiochronology for the Mediterranean region

Research Article| January 01, 2003 Late Miocene calcareous nannofossil biostratigraphy and astrobiochronology for the Mediterranean region I. Raffi; I. Raffi 1Department of Earth Science, University “G. d’Annunzio”, Via dei Vestini 31, 66013 Chieti, Italy, e-mail: raffi@unich.it; cristina.mozzato@unipd.it Search for other works by this author on: GSW Google Scholar C. Mozzato; C. Mozzato 1Department of Earth Science, University “G. d’Annunzio”, Via dei Vestini 31, 66013 Chieti, Italy, e-mail: raffi@unich.it; cristina.mozzato@unipd.it2Department of Geology, Paleontology, and Geophysics, University of Padova, Via Giotto 1, 35137 Padova, Italy, e-mail: eliana.fornaciari@unipd.it; domenico.rio@unipd.it Search for other works by this author on: GSW Google Scholar E. Fornaciari; E. Fornaciari 2Department of Geology, Paleontology, and Geophysics, University of Padova, Via Giotto 1, 35137 Padova, Italy, e-mail: eliana.fornaciari@unipd.it; domenico.rio@unipd.it Search for other works by this author on: GSW Google Scholar F. J. Hilgen; F. J. Hilgen 3Department of Geology, Faculty of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands, e-mail: fhilgen@geo.uu.nl Search for other works by this author on: GSW Google Scholar D. Rio D. Rio 2Department of Geology, Paleontology, and Geophysics, University of Padova, Via Giotto 1, 35137 Padova, Italy, e-mail: eliana.fornaciari@unipd.it; domenico.rio@unipd.it Search for other works by this author on: GSW Google Scholar Micropaleontology (2003) 49 (1): 1–26. https://doi.org/10.2113/49.1.1 Article history received: 16 Oct 2001 rev-recd: 21 Feb 2003 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation I. Raffi, C. Mozzato, E. Fornaciari, F. J. Hilgen, D. Rio; Late Miocene calcareous nannofossil biostratigraphy and astrobiochronology for the Mediterranean region. Micropaleontology 2003;; 49 (1): 1–26. doi: https://doi.org/10.2113/49.1.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyMicropaleontology Search Advanced Search Abstract Results are presented of a quantitative biostratigraphic study of the calcareous nannofossils from the upper Miocene Metochia section (Gavdos Island, Greece) located in the eastern Mediterranean. The study allows the completion of the calcareous nannofossil Zonal Scheme for the Mediterranean Neogene. Parts of the scheme have already been proposed earlier for the Pliocene-Pleistocene (Rio et al. 1990b) and for the latest Oligocene to early late Miocene (Fornaciari and Rio 1996, Fornaciari et al. 1996).The Metochia section proved to be a suitable section for high-resolution biostratigraphic studies. It has a detailed planktonic foraminiferal biostratigraphy and a robust chronology based on the astronomical calibration of the sedimentary cycles (Krijgsman et al. 1995, Hilgen et al. 1995). Age estimates for the nannofossil biohorizons recognized in the section were obtained through direct correlation to this astrochronology. Five out of seventeen biohorizons were selected for biostratigraphic purposes and to define the (sub)zonal boundaries. They are (in stratigraphic order): LO (Last Occurrence) of Discoaster hamatus Martini and Bramlette 1963, equivalent to the base of Subzone MNN10a, dated at 9.53 Ma; FCO (First Consistent Continuous Occurrence) of Discoaster pentaradiatus (Tan 1927) Bramlette and Riedel 1954, equivalent to the base of Subzone MNN10b, at 9.37 Ma; PB (Paracme Beginning) of Reticulofenestra pseudoumbilicus (Gartner 1967) Gartner 1969, equivalent to the base of Zone MNN11a, at 8.76 Ma; FO (First Occurrence) of Amaurolithus spp. (A. primus (Bukry and Percival 1971) Gartner and Bukry 1975), equivalent to the base of Subzone MNN11b, at 7.42 Ma, and FO of Nicklithus amplificus (Bukry and Percival 1971) Raffi Backman and Rio 1998, equivalent to the base of Subzone MNN11c, at 6.69 Ma. We compared our biochronology with data available from other Mediterranean sections (Sprovieri et al. 1996, Negri et al. 1999, Negri and Villa 2000, Bonomo 2001), and with the nannofossil biochronology from low-latitude oceanic reference sections (Raffi et al. 1995, Backman and Raffi 1997). Our results evidence differences and similarities: some of the recently proposed events in the Tortonian-Messinian (e.g., FO and FCO of Reticulofenestra rotariaTheodoridis 1984, FO of Amaurolitus delicatus Gartner and Bukry 1975) proved not to be reliable and do not improve the biostratigraphic resolution by calcareous nannofossils in the time interval under consideration. On the other hand, the five selected biohorizons can easily be reproduced elsewhere in the Mediterranean, and are considered useful for correlations to the extra-Mediterranean realm. You do not currently have access to this article.

Late Miocene calcareous nannofossil biostratigraphy and astrobiochronology for the Mediterranean region

Results are presented of a quantitative biostratigraphic study of the calcareous nannofossils from the upper Miocene Metochia section (Gavdos Island, Greece) located in the eastern Mediterranean. The study allows the completion of the calcareous nannofossil Zonal Scheme for the Mediterranean Neogene. Parts of the scheme have already been proposed earlier for the Pliocene-Pleistocene (Rio et al. 1990b) and for the latest Oligocene to early late Miocene (Fornaciari and Rio 1996, Fornaciari et al. 1996).The Metochia section proved to be a suitable section for high-resolution biostratigraphic studies. It has a detailed planktonic foraminiferal biostratigraphy and a robust chronology based on the astronomical calibration of the sedimentary cycles (Krijgsman et al. 1995, Hilgen et al. 1995). Age estimates for the nannofossil biohorizons recognized in the section were obtained through direct correlation to this astrochronology. Five out of seventeen biohorizons were selected for biostratigraphic purposes and to define the (sub)zonal boundaries. They are (in stratigraphic order): LO (Last Occurrence) of Discoaster hamatus Martini and Bramlette 1963, equivalent to the base of Subzone MNN10a, dated at 9.53 Ma; FCO (First Consistent Continuous Occurrence) of Discoaster pentaradiatus (Tan 1927) Bramlette and Riedel 1954, equivalent to the base of Subzone MNN10b, at 9.37 Ma; PB (Paracme Beginning) of Reticulofenestra pseudoumbilicus (Gartner 1967) Gartner 1969, equivalent to the base of Zone MNN11a, at 8.76 Ma; FO (First Occurrence) of Amaurolithus spp. (A. primus (Bukry and Percival 1971) Gartner and Bukry 1975), equivalent to the base of Subzone MNN11b, at 7.42 Ma, and FO of Nicklithus amplificus (Bukry and Percival 1971) Raffi Backman and Rio 1998, equivalent to the base of Subzone MNN11c, at 6.69 Ma. We compared our biochronology with data available from other Mediterranean sections (Sprovieri et al. 1996, Negri et al. 1999, Negri and Villa 2000, Bonomo 2001), and with the nannofossil biochronology from low-latitude oceanic reference sections (Raffi et al. 1995, Backman and Raffi 1997). Our results evidence differences and similarities: some of the recently proposed events in the Tortonian-Messinian (e.g., FO and FCO of Reticulofenestra rotaria Theodoridis 1984, FO of Amaurolitus delicatus Gartner and Bukry 1975) proved not to be reliable and do not improve the biostratigraphic resolution by calcareous nannofossils in the time interval under consideration. On the other hand, the five selected biohorizons can easily be reproduced elsewhere in the Mediterranean, and are considered useful for correlations to the extra-Mediterranean realm.

Deep-water changes: the near-synchronous disappearance of a group of benthic foraminifera from the Late Miocene Mediterranean

Benthic foraminiferal and geochemical data from the Monte del Casino section in northern Italy are employed to reconstruct the sequence of events preceding the Late Miocene Mediterranean salinity crisis. We evaluate the effects of eustatic sea-level changes and tectonic events, affecting the Atlantic–Mediterranean connections. Changing benthic foraminiferal assemblages record changes in the deep-water environment, that can be explained by progressive isolation of the Mediterranean basin. The results of the analyses of stable oxygen- and carbon isotopes and redox-sensitive elements are in line with the benthic faunal trends. At 7.16 Ma, a first major step in isolation of the basin is indicated by the nearly simultaneous disappearance of a group of deeper-water benthic species usually found in middle to lower slope environments. At the same time, stable isotopes and redox-sensitive elements indicate cooling and decreasing bottom water oxygenation. After 6.8 Ma gradual development of water-mass stratification, probably accompanied by increasing bottom-water salinity, is indicated by all proxies. The cyclic pattern of homogeneous and sapropelitic sediments in the section is related to astronomical parameters, and allows a detailed correlation with Mediterranean sections at considerable geographic distances. We compared the benthic foraminiferal faunas with those from the Metochia section (Gavdos, Greece), deposited at a similar water depth (∼1000 m), to find that the benthic foraminifera at both sites indicate a similar, synchronous paleoenvironmental development. All proxies indicate that the onset of the Late Miocene Mediterranean salinity crisis dates back to the earliest Messinian. The development of the Mediterranean basin toward an evaporite trap is a result of interactions between a 400-kyr eccentricity related climatic effect superimposed upon gateway dynamics at the Atlantic–Mediterranean connections. Benthic foraminifera accurately record the steps in increasing isolation of the Mediterranean basin.

Organic-rich layers in the Metochia section (Gavdos, Greece): evidence for a single mechanism of sapropel formation during the past 10 My

Three well-developed 10 Ma old sapropels from the island of Gavdos (Greece) were selected for a detailed geochemical, micropaleontological and sedimentological study. The sapropels are characterized by a high organic carbon and a low carbonate content. Productivity was higher during sapropel formation, as indicated by increased Ba contents and higher percentages of the planktonic foraminiferal species Neogloboquadrina acostaensis. Enrichment of Mo and V in the sapropels indicates less oxygenated bottom water conditions, which is supported by the flourishing of low oxygen tolerant benthic foraminifera. Variation in grainsize and the Ti/Al ratio point to an alternating dominance of fluvial (sapropels) and eolian-derived (homogeneous intervals) terrigenous clastics. Evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed-load type rivers. The increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion. The results obtained for the Gavdos sapropels are consistent with those of previous studies of younger sapropels and related CaCO 3 cycles in the Mediterranean. The consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 My, namely precession induced dry–wet oscillations in the Mediterranean climate. Still, the effect of this mechanism on the intensity of surface water productivity, dilution and diagenetic signals may differ from site to site, depending on location, depositional environment and intensity of the astronomical forcing.

Late Miocene magnetostratigraphy, biostratigraphy and cyclostratigraphy in the Mediterranean

A new chronology for the late Miocene of the Mediterranean is presented by combining magnetostratigraphic, biostratigraphic (planktonic foraminifera and dinoflagellates) and cyclo-stratigraphic data. Long and continuous upper Miocene sections on Gavdos (Metochia section) and Sicily (Gibliscemi section) display cyclic alternations of homogeneous marls and sapropels and can be correlated on the basis of their distinct cyclic patterns. The Metochia section yields a good paleomagnetic signal and the position of 17 polarity reversals can be determined. The resulting polarity sequence allows an unambiguous correlation to the geomagnetic polarity time scale (GPTS). The paleomagnetic signal in the Gibliscemi section is too weak to determine a reliable polarity sequence, except for the lowermost part of the section. Detailed biostratigraphic analysis results in the identification of 13 planktonic foraminiferal and 9 dinoflagellate bioevents, which can all be accurately dated. The Tortonian/Messinian boundary, defined by the First Regular Occurrence (FRO) of the G. conomiozea group, is determined in chron C3Br.1r with an age of 7.12 Ma, according to the GPTS (CK95) of Cande and Kent [1].