1,721,144 research outputs found
Benthic environmental changes in the Eastern Mediterranean Sea during sapropel S5 deposition
No full textHigh resolution benthic foraminiferal analyses of sediment cores collected at different sites in the Eastern Mediterranean Sea revealed that profound changes occurred in deep-sea ventilation over the past 124-119 ka BP. The three cores (SIN97-GC01, BAN89-GC09, BD02-GC01) were selected in order to investigate middle and deep bathyal ecosystems in the Eastern Mediterranean basin. At site SIN97-GC01 (933 m water depth, Urania Basin), the presence of benthic fauna in the sapropel layer, and the gradual increase in benthic foraminiferal abundance from the middle part of the sapropel, suggest that the sea-floor was partially ventilated and that re-oxygenation had increased considerably during the late phase of S5 deposition. Cores BAN89-GC09 (2011 m water depth, Napoli Dome) and BD02-GC01 (2470 m water depth, Ionian Sea) show a different pattern. During sapropel S5, benthic abundance and diversity strongly decrease and microfauna even disappears in some levels, suggesting the establishment and maintenance of stagnant and anoxic conditions at the seafloor until the end of S5 deposition. In the deepest part of the basin. the re-establishment of the benthic foraminiferal community at the top of the 55 layer indicates a relatively slow bottom re-oxygenation. At the southernmost site, the foraminiferal assemblage records a short oxygenation pulse during the deposition of sapropel S5 linked to a short cold spell. The results of this study suggest that the evolution of the dysoxic-anoxic conditions, as well as the re-oxygenation pattern at the end of the stagnant period, were characterised by spatial and temporal variability, possibly controlled by basin physiography
Foraminiferal ecozones, a high resolution proxy for the Late Quaternary biochronology in the central Mediterranean Sea
No full textThe planktic foraminiferal distribution identified in 60 cores collected in different basins of the Mediterranean Sea allowed to establish an ecostratigraphical scheme which provides a very important tool for the biochronological subdivision of the uppermost Quaterary. We identified a succession of ten ecozones during the last 23 ka in the Tyrrhenian basin and eight ecozones in the Adriatic Sea during the last 15 ka. The ecozones boundaries have been calibrated by C-14 AMS radiometric data and by the stable oxygen isotope record. The chronological framework defined by the successive bioevents shows a very high resolution (millenary scale) and evidences that the changes in the planktic microfauna occurred more or less synchronously throughout the central Mediterranean Sea. Differences due to different oceanographic settings of the basins do not affect the general distributional pattern of planktic foraminifera
Are productivity and stratification important to sapropel deposition? Microfossil evidence from late Pliocene I-cycle 180 at Vrica, Calabria
No full textWe present the results of a micropaleontological study performed on the sapropel sequence associated with insolation cycle 180 from the Plio-Pleistocene Vrica sequence (Calabria, Italy). We performed a high-resolution study on the 3.38-m-thick layer c from a core drilled close to the classical outcrop section in which we analyze fluctuations in the abundance and composition of calcareous nannofossils and planktic and benthic foraminifera. Changes in the fossil assemblages reveal at least three major paleoenvironmental phases in layer c. The base of the sapropel contains an abrupt decrease in benthic fauna that continues through all of layer c. It also has an increase of the coccolithophorids species Coccolithus pelagicus. Planktic foraminifera show at the same depth a peak of the cold species Globorotalia scitula. These changes are followed by decreases in the carbonate preservation index and in abundances of Globigerinita glutinata, Globigerinita uvula and Neogloboquadrina pachyderma (sinistral), which suggest cold and highly productive upwelling waters. A short interval in the middle of the sapropel is characterized by low values of C. pelagicus, a fluctuating increase of Pseudoemiliania lacunosa and among the foraminifera an increase of Globigerinoides ruber together with the presence (although decreased) of G. glutinata, G. uvula and N. pachyderma (sinistral). We interpret these features as suggesting high seasonality with warm stratified and probably oligotrophic waters during summer and relatively cold conditions during winter. Finally, the topmost interval of the Vrica layer c exhibits the re-appearance of P. lacunosa together with abundant siliceous phytoplankton. Planktic microfauna show the disappearance of the cold species G. glutinata, G. uvula and N. pachyderma (sinistral). Thus this interval appears to be characterized by warmer temperature. The transition from the laminated to the massive sediment displays a sequence of events, including a decrease of the carbonate preservation index and peaks of Globorotalia inflata and G. scitula, suggesting again upwelling and mixing of the whole water column and, thus, transition to the oxygenated conditions characterizing the massive layer. Neither increased productivity nor stratification appear to characterize the whole sapropel interval, which is, however, always dysoxic
Relationship between foraminifera and organic carbon in core AD91-16 of South Adriatic Sea
No full textCalcareous nannofossil and foraminifer biostratigraphy of the Campanian–Maastrichtian chalk of the Femern Bælt (Denmark–Germany)
No full textA new study based on calcareous nannofossil and benthic and planktonic foraminifer biostratigraphy is presented for the upper Campanian – Maastrichtian chalk of the Femern Bælt (Denmark and Germany; Fig.1). The results are consistent with recent studies of the Danish chalk for this interval, allowing correlation across the Danish Basin and forming the basis for correlation further afield within the Boreal Realm. Numerous studies have been carried out recently on the upper Campanian – Maastrichtian chalk of the Danish Basin, covering aspects such as sedimentology, depositional environment, macrofossil biostratigraphy, carbon isotope stratigraphy as well as nannofossil and dinoflagellate biostratigraphy. However, very few published studies on foraminifers exist across this interval in this area. The 09.A.006, 09.A.007 and 09.A.008 boreholes (Fig. 2) were drilled in 2009 in preparation for construction of a fixed link across the Femern Bælt, which will connect Denmark to Germany (Rambøll Arup JV 2011). The boreholes penetrated glacial till, Paleocene–Eocene clay and chalk (Sheldon et al. 2012). Here, for the first time, the Boreal foraminifer biostratigraphy of the late Campanian – Maastrichtian interval is investigated and presented alongside nannofossil biostratigraphy
Evolution des rivages d’Alexandrie à l’Holocène récent, marge occidentale du delta du Nil, Egypte
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