170 research outputs found
Fish otoliths from the Pliocene Heraklion Basin (Crete Island, Eastern Mediterranean)
No full textThe Pliocene Eastern Mediterranean fish record is revealed through the study of a 60-m thick stratigraphic sequence near the village Voutes (Heraklion, Crete). Forty-two species belonging to twenty families are identified. Calcareous nannoplankton biostratigraphy places the studied sequence within the biozone MNN16a (latest Zanclean). The stratigraphic distribution of 31species is modified. Among these, 12species are reported for the first time in the Eastern Mediterranean Zanclean, while 19species are first reported outside the Ionian Sea. The Voutes fish fauna presents a diversified benthic and benthopelagic assemblage filling a significant gap in the fossil recor
Paleobathymetric interpretation of the fish otoliths from the Lower - Middle Quaternary deposits of Kephallonia and Zakynthos islands (Ionian Sea, Western Greece)
No full textFish otoliths arc herein used to estimate the depositional depth of the Early - Middle Pleistocene deposits at SE Zakynthos and SW Kephallonia Islands (Ionian Sea, Western Greece), through comparison with the modern bathymetric distributions of the identified fish taxa. These estimates provide a more detailed picture of the depth variations for the Gelasian - Ionian stage interval in the study areas. The Lower Pleistocene marine deposits of the Gerakas Formation (SE Zakynthos Island, Ionian Sea) were deposited at average depths of 400-450 meters, with eustacy playing an important role in the depth variability, between 1.95-1.73 Ma. An uplifting episode, followed by subsidence takes place between 1.73-1.66 Ma, taking the area to 200-300 meters of depth, and then back to 400-500 meters. However, the area seems uplifted again to 200-400 meters later on in the Calabrian stage (1.25-0.97 Ma). Sedimentation of the Akrotiri deposits (NW Kephallonia Island, Ionian Sea), during the same chronostratigraphic interval, took place in a similar setting. At the Early Pleistocene (1.95-1.73 Ma) this basin reached depths of 400-450 meters, with uplift and following subsidence taking place between 1.73-1.66 Ma. Overall, the application of fish otolith paleobathymetry in the study areas provide a detailed picture of the depth variations for the Early Quaternary interval and refine the currently hypothesized pattern of tectonic movements
The early Quaternary palaeobiogeography of the eastern Ionian deep-sea Teleost fauna: A novel palaeocirculation approach
No full textThe early Quaternary stratigraphic and geographic distribution of teleostean fishes in the Ionian Sea (eastern
Mediterranean) is examined based on the fossil otolith record. Through comparison between the western and
the eastern Ionian early–middle Pleistocene deep-sea ichthyofauna, the stratigraphic distributions of
nineteen taxa are revised. A new method of assemblage analysis is attempted, in order to discern the
palaeoceanographic conditions prevailing at this time. The relative contributions of tropical, subtropical,
temperate, and subpolar taxa to the surface, intermediate, and deepwater fish palaeofauna are calculated,
using fossil material from Akrotiri (Kephallonia Island, Greece), Gerakas (Zakynthos Island, Greece) and
Montalbano Jonico (Italy) sections, which span the Gelasian–Ionian time interval. Eleven distinct phases in
the Ionian Sea palaeoceanographic evolution are distinguished, from prior 1.95 Ma to 0.61 Ma. Furthermore, a
case study is conducted, to test the hypothesis that palaeoichthyofauna can be used to draw conclusions
regarding the palaeocirculation patterns and their variability. In the Ionian Sea, the local production and/or
Atlantic origin of the deep cold waters is registered already during the Gelasian. The presence of oceanic fish in
the eastern Ionian can be explained by the existence of a strong anticyclonic gyre in the area during the early
Quaternary, further indicating that the basin's geometry exhibited sufficient bathymetric variation to allow
for the activation of the gyre
Remarks on the Messinian evaporites of Zakynthos Island (Ionian Sea, Eastern Mediterranean)
No full textDetailed mapping of the Neogene deposits on Zakynthos Island shows that the Messinian primary evaporite basins, formed over Ionian basement, are delimited by the westernmost outcrop of the Triassic evaporitic diapirs, located west of the Kalamaki-Argasi Messinian gypsum unit. The post-Miocene external Ionian thrust is emplaced west of the Triassic diapirs. Planktonic foraminifera biostratigraphy indicates that primary evaporite accumulation took place probably during the first stage of the Messinian salinity crisis (5.96-5.60 Ma), in shallower parts of a foreland basin, formed over the Pre-Apulian and the Ionian zone basement. Establishment of these depositional environments, before the Ionian thrust emplacement, was probably due to the particularities of the foreland basin, which extended from the external Ionian to the internal Pre-Apulian zone. Field observations, borehole data and an onshore seismic profile show that the Neogene sediments over the Pre-Apulian basement correspond to the foredeep through forebulge domain of the foreland basin, as it is documented from their spatial thickness distribution. In contrast, the Neogene sediments over the Ionian basement correspond to the wedge top of the foreland basin, which was less subsiding, as it is deduced by their reduced thickness. This lower subsidence rate was the result of the concurrent diapiric movements of the Ionian Triassic evaporites. In Agios Sostis area, located over Pre-Apulian basement, the Neogene sequence is intercalated by decametre-thick resedimented blocks consisting of shallow water selenite. To the southeast, this mass-wasting Messinian gypsum passes to mainly gypsum turbidite. In Kalamaki-Argasi area, located over Ionian basement, the shallow water environment led to the deposition of the observed primary gypsum. Erosion of the primary gypsum of both forebulge and wedge top supplied the foreland basin’s depocenter with gypsum turbidites.
Η λεπτομερής χαρτογράφηση των Νεογενών αποθέσεων της Ζακύνθου δείχνει ότι οι λεκάνες πρωτογενούς Μεσσήνιας εβαποριτικής απόθεσης, που σχηματίστηκαν πάνω σε Ιόνιο υπόβαθρο, οριοθετούνται από τη δυτικότερη εμφάνιση των Τριαδικών εβαποριτικών διάπειρων (δυτικά της Μεσσήνιας ενότητας γύψου Καλαμάκι-Αργάσι). Η μετα-Μειοκαινική εξωτερική Ιόνια επώθηση τοποθετείται δυτικά αυτών των Τριαδικών διάπειρων. Βιοστρωματογραφική ανάλυση των συναθροίσεων πλαγκτονικών τρηματοφόρων στα Νεογενή ιζήματα δείχνει ότι η συσσώρευση πρωτογενούς εβαπορίτη έλαβε χώρα πιθανά κατά το πρώτο στάδιο της κρίσης αλμυρότητας του Μεσσηνίου (5.96-5.60 Εκατ.χρ.), στα αβαθέστερα τμήματα της λεκάνης προχώρας, η οποία σχηματίστηκε πάνω στο Προ-Απούλιο και Ιόνιο αλπικό υπόβαθρο. Ο σχηματισμός των περιβαλλόντων ιζηματογένεσης, πριν από την Ιόνια επώθηση, πιθανά οφείλεται στις ιδιαιτερότητες της λεκάνης προχώρας, η οποία εκείνο το διάστημα εκτείνονταν από την εξωτερική Ιόνια ως την εσωτερική Προ-Απούλια ζώνη. Νέα δεδομένα υπαίθρου, σε συνδυασμό με τη βιοστρωματογραφία, τα στοιχεία γεωτρήσεων και μία διαθέσιμη σεισμική τομή δείχνουν ότι τα Νεογενή ιζήματα πάνω στο Προ-Απούλιο υπόβαθρο αντιστοιχούν στον τμήμα της λεκάνης προχώρας, από το προβύθισμα (foredeep) ως την πρόσθια ανύψωση (forebulge), όπως αυτό διαπιστώνεται από την χωρική κατανομή του πάχους τους. Αντίθετα, τα Νεογενή ιζήματα πάνω στο Ιόνιο υπόβαθρο αντιστοιχούν στο τμήμα της λεκάνης προχώρας που βρίσκεται πάνω στο μετωπικό πρίσμα της ορογένεσης (wedge top), το οποίο βυθίζονταν λιγότερο όπως συνάγεται από το ελαττωμένο πάχος των ιζημάτων. Ο μικρότερος ρυθμός βύθισης οφείλεται στις διαπειρικές κινήσεις των Τριαδικών εβαποριτών. Στη Νεογενή ακολουθία, που βρίσκεται πάνω σε Προ-Απούλιο υπόβαθρο (περιοχή Άγιος Σώστης), παρεμβάλλονται επανιζηματοποιημένα μπλοκ δεκαμετρικού πάχους αποτελούμενα από σεληνίτη μικρού βάθους απόθεσης. Προς νότο, αυτή η βαρυτικά μεταφερόμενη μάζα της Μεσσήνιας γύψου μεταπίπτει κυρίως σε τουρβιδιτική γύψο. Στην περιοχή Καλαμάκι-Αργάσι που βρίσκεται πάνω σε Ιόνιο υπόβαθρο, το αβαθές περιβάλλον οδήγησε στην απόθεση της παρατηρούμενης πρωτογενούς γύψου. Η διάβρωση της πρωτογενούς γύψου τόσο της πρόσθιας ανύψωσης όσο και του μετωπικού πρίσματος επώθησης τροφοδότησαν το προβύθισμα της λεκάνης προχώρας με τουρβιδίτες γύψου
Morphological and physiological variability of species of Meloidogyne in West Africa and implications of their control
No full textThe extreme morphological and physiological variability of certain rootknot nematodes (Meloidogyne spp.) and its implication on the development of control methods of these parasites, based upon crop rotations and the use of resistant varieties of otherwise susceptible crops are discussed.In a review of the systematics of the genus Meloidogyne reestablished in 1949 by Chitwood to replace the polyphagous species Heterodera marioni Cornu, 1887, the variability of the so-called perineal pattern of the females, the most important character to distinguish species within the genus, is emphasized.The results of the cytological investigations of Triantaphyllou are briefly discussed. It has been shown that most species studied are characterized by a parthenogenetic mode of reproduction. Two types of non-amphimictic reproduction have been observed: mitotic and meiotic parthenogenesis. Meloidogyne incognita, M. javanica and M. arenaria are characterized by mitotic parthenogenesis.An analysis of the number of publications appearing between 1949 and 1976. dealing with identified species of Meloidogyne has revealed that 93% of the articles concern Chitwood's species of 1949, and that 76% refer to M. incognito, M. javanica and M. arenaria.Faunistic studies in West Africa have shown that the most frequently encountered root-knot nematodes belong to the species M. incognita, M. javanica and M. arenaria. Identification of West African populations are complicated by the occurrence of mixtures of species, the great morphological variability and the existance of populations possessing rather large proportions of individuals exhibiting characters intermediate between species.Certain morphometric characters of perineal patterns (width of vulva and distance between phasmids) were measured in a number of clones of Meloidogyne populations. These observations have demonstrated that although these characters are stable within clones, they cannot distinguish M. javanica from M. incognita.The distance of the excretory pore of females from the anterior end, expressed in stylet lengths might possibly be an aid to distinguish M. incognita from M. arenaria and M. javanica.The author is reluctant to describe populations characterized by unusual perineal patterns as new species and suggests inclusion of host-plant and cytological data in the description of new species.Data presented indicate that length of juveniles could not be used to distinguish among M. incognita, M. javanica and M. arenaria.Observations of juveniles from a population of M. incognita acrita have demonstrated that the inflation of the rectum is not an absolute criterium to distinguish M. incognita and M. acrita. A critical evaluation of the data of TERENTEVA (1967) concerning the height of the lip region of males of M.incognita and M. incognita acrita makes the author reject the statement that this character might be useful to distinguish between these two taxa.The author concludes that up till now, no infallible methods have been found to identify naturally occurring populations of Meloidogyne in West Africa.After the splitting of the polyphagous Heterodera marioni into a number of species of Meloidogyne it became possible to assemble host lists for each species. In principal this information should provide a basis for crop rotation recommendations, intended to reduce root-knot nematodes infestation, provided that the Meloidogyne populations could be identified to the species level. Comparison of the host ranges of M. incognita, M. javanica and M. arenaria emphasized that these species have a great number of host plants in common, many of which are important crops. Only a few species could be used as differential plants to distinguish among these three species.Published data and original results presented show that when many populations of the same species of Meloidogyne are studied, resistance/susceptibility of a given plant species cannot be predicted with confidence. Certain populations are able to parasitize a given plant and others are not.The same phenomenon is observed with resistant varieties of otherwise susceptible crops. When several populations of the same species of Meloidogyne are tested against such a variety, those populations capable of parasitizing the resistant varieties are often called 'B races'. Studies concerning development of 'B races' on resistant tomatoes in Senegal have shown that some populations of Meloidogyne are able to parasitize resistant varieties strongly and immediately. others are able to form 'B races' after a selection has taken place, the majority however, is not capable of parasitizing resistant tomatoes.Indications have been obtained that a gene for gene relation exists between nematode populations and resistant tomato varieties and a code indicating nematode and resistant variety genotype is proposed.It is assumed that most plant species are attacked by Meloidogyne populations; the reaction of the plant attacked towards the specific Meloidogyne population concerned, determines if a successful parasitic relation develops.It is proposed to consider as a group the tropical polyphagous species of Meloidogyne, which are characterized by a certain degree of polyploidy and a mitotic parthenogenetic mode of reproduction. This group should comprise M. incognito, M. javanica, M. arenaria, populations intermediate between these species, possibly undescribed species and certain described species for which information on mode of reproduction and physiological characters (host-range) is lacking.On the basis of an actual field trial in Senegal, it is shown that recommendations for crop sequences or rotations should be based on testing different crops and varieties against naturally occurring populations of root-knot nematodes. Incorrect choice of crops may be made if rotations are based upon Meloidogyne identifications only. It is recommended that different populations in an area be tested on cash, food, and cover crops and resistant varieties.Selection of resistant varieties should be based on reactions to as many different populations of Meloidogyne as possible. Using such a technique 'B races' may be detected, and in addition much material not possessing root-knot resistance in the area where the varieties are developed, may be found to have resistance against other populations elsewhere.In order to obtain the maximum value of non-hosts and resistant varieties, it is recommended to use these plants as a preventive measure rather than as a cure. Therefore, their use should be recommended in slightly infested or Meloidogyne- free soils.The author has observed in fact, that non-hosts planted in heavily infested soil may be badly damaged because of a necrotic reaction to invading juveniles. In extreme cases this may give rise to dead patches in the field and a resultant increase of weed growth, accompanied by an increase of Meloidogyne on susceptible weeds. Thus, usefulness of the non-host can be nullified. Moreover the risk of selecting 'B races' is much higher in heavily infested land than in nonor slightly infested fields.Thus it is recommended to use non-hosts and resistant varieties as preventive treatments within an integrated control including the various chemical and physical treatments available
The Barremian and Aptian stepwise development of the 'Oceanic Anoxic Event 1a' (OAE 1a) crisis: integrated benthic and planktic high-resolution palaeoecology along the Gorgo a Cerbara stratotype section (Umbria-Marche Basin, Italy)
No full textThe Barremian and Aptian were times of global plate reconfiguration and profound changes in the ocean-climate system, culminating in the worldwide deposition of lower Aptian black shale layers (OAE 1a). Based on high-resolution lithostratigraphic and micropaleontological analyses, precursor conditions and timing of the anoxia are here reconstructed along a 33.06 m thick section in the proposed Barremian/Aptian boundary GSSP stratotype at Gorgo a Cerbara (Umbria-Marche Basin, Italy).
A non-uniform history of benthic foraminiferal diversification is interrupted by the Selli Level (= OAE 1a) and by three turnover points for both benthic and planktic organisms, each highlighted by prominent breaks in lithology and outcrop morphology. The first two points, at similar to 1.1 Myr and similar to 20-50 kyr prior to the onset of the OAE 1a, correspond respectively to the nannoconid (= bathypelagic calcareous nannofossils) 'decline' and 'crisis' events, and separate: (a) pelagic limestone/chert-claystone lithological cycles of the uppermost Maiolica Formation, showing frequencies reminiscent of orbital eccentricity and containing an oligotrophic Barremian benthic and planktic assemblage, dominated by k-selected nannoconids and Rhizammina; (b) greenish-grey cherty marls of the lowermost Marne a Fucoidi Formation, associated to declining sedimentation rates and eutrophic early Aptian assemblages dominated by radiolarians and lituolid benthic foraminifera; and (c) anoxic radiolarites and shales of the carbonate-free Selli Level. High magnitude and frequency assemblage fluctuations occur between the nannoconid crisis (similar to 25 cm below the lowermost OAE 1a black shale layer) and the Selli Level base, with suggestions of bottom-water acidification. At similar to 800 kyr after the OAE 1a end, a third turnover point in the basal reddish member of the Marne a Fucoidi highlights 'middle' Aptian assemblages characterized by a bloom of early macroperforate planktic foraminifera (Hedbergella spp.) and appearances of new benthic species, marking a shift towards better oxygenation.
OAE 1a oxygen and pelagic carbonate factory crises are here suggested to have been step-wise and linked to global warming conditions
Field-based validation of a diagenetic effect on G. ruber Mg/Ca paleothermometry: Core top results from the Aegean Sea (eastern Mediterranean)
No full textRecent work across the Mediterranean Sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal Mg/Ca, which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions. To test and verify these effects, we present new Aegean Sea results which reveal Mg/Ca values that were unreasonably high to be explained by temperature or salinity variations alone, confirming that foraminiferal Mg/Ca is affected by diagenesis. We have specifically targeted Globigerinoides ruber (w, sensu stricto), from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range, along a north?south Aegean Sea transect. Scanning Electron Microscopy analyses show that G. ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates. This secondary calcite phase seems to be responsible for the anomalously high Mg/Ca ratios and likely formed near the sediment/water interface from CaCO3 supersaturated interstitial seawater. We also have clear evidence of diagenetic alteration in a north?south direction along the Aegean Sea, possibly depending on salinity and calcite saturation state gradients. These observations illustrate the necessity of alternative techniques (e.g., flow?through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry) to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity, excessive evaporation, and restricted circulation
Calcareous nannoplankton dating of the Late Quaternary deposits in Greece and the eastern Mediterranean: Case studies from terrestrial and marine sites
No full textAbstractThe distribution and abundance of Emiliania huxleyi (E. huxleyi) assemblages in the marine sediments of the Aravonitsa Plateau, Greece, and from the eastern Mediterranean are used (1) to evaluate the calcareous nannoplankton NN21a and NN21b biozones and the NN21a/NN21b boundary, and (2) to analyze the palaeoenvironmental and palaeoclimatic conditions prevailing in this interval. The sediment succession displays varied E. huxleyi assemblages and these are interpreted as reflecting climatic variability during marine isotope stages MIS 1–8
PRELIMINARY STUDY ON THE SLUMP STRUCTURES OF THE EARLY OLIGOCENE SEDIMENTS OF THE PRE-APULIAN ZONE (ANTIPAXOS ISLAND, NORTH-WESTERN GREECE)
No full textA spectacular slump is observed in the Alpine sediments of the Antipaxos Island (Pre-Apulian zone, Western Greece). It can be followed in a zone of about 2000 m, in the eastern coast of the island. The slumped unit exposure length extends for more than 200 m, and is directly overlain and underlain by undeformed strata. The slump has an average thickness of 15 m and is composed, as the surrounding undeformed units, of calcareous mudstones and fine-grained calcareous sandstones. Synsedimentary folds that very often are transformed to contorted beds affect slump sediments. Fold and contorted bed axes present a NNW-SSE direction, coinciding with the general direction of the Pre-Apulian zone. Slump and overlain/underlain undeformed sediments originate from the flux of clastic mainly pelagic/neritic biogenic particles, emanating from turbidity currents. More than 50 samples have been collected and analyzed for calcareous nannofossil content. All samples were featured by the contemporaneous presence of abundant nannofossil flora implying the biostratigraphic correlation with the NP23 nannofossil biozone. The biostratigraphic assignment places the slump and the surrounding sediments to the Early Oligocene. As the Pre-Apulian zone corresponds to the slope between the Apulian Platform and the Ionian Basin, the presence of the slump is directly related to the same age sloping and tectonic mobility of this domain. The Antipaxos turbidites sediments are well integrated to the flysch deposition of the external Hellenide foreland basin system
Bioinvasion impacts on biodiversity, ecosystem services, and human health in the Mediterranean Sea
No full textBiological invasions have become a defining feature of marine Mediterranean ecosystems with significant impacts on biodiversity, ecosystem services, and human health. We systematically reviewed the current knowledge on the impacts of marine biological invasions in the Mediterranean Sea. We screened relevant literature and applied a standardised framework that classifies mechanisms and magnitude of impacts and type of evidence. Overall, 103 alien and cryptogenic species were analysed, 59 of which were associated with both negative and positive impacts, 17 to only negative, and 13 to only positive; no impacts were found for 14 species. Evidence for most reported impacts (52%) was of medium strength, but for 32% of impact reports evidence was weak, based solely on expert judgement. Only 16% of the reported impacts were based on experimental studies. Our assessment allowed us to create an inventory of 88 alien and cryptogenic species from 16 different phyla with reported moderate to high impacts. The ten worst invasive species in terms of reported negative impacts on biodiversity include six algae, two fishes, and two molluscs, with the green alga Caulerpa cylindracea ranking first. Negative impacts on biodiversity prevailed over positive ones. Competition for resources, the creation of novel habitat through ecosystem engineering, and predation were the primary reported mechanisms of negative effects. Most cases of combined negative and positive impacts on biodiversity referred to community-level modifications. Overall, more positive than negative impacts were reported on ecosystem services, but this varied depending on the service. For human health, only negative impacts were recorded. Substantial variation was found among Mediterranean ecoregions in terms of mechanisms of impact and the taxonomic identity of impacting species. There was no evidence that the magnitude of impact increases with residence time. Holistic approaches and experimental research constitute the way forward to better understanding and managing biological invasions
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