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Early Paleogene δ13C and δ18O records based on marine ostracodes: implications for the upper Danian succession at Sidi Nasseur (Tunisia) and their application value in paleoceanography
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Ostracode and other microfossil assemblages from the Tunisian Trough have previously been studied to characterize paleoenvironmental conditions during the late Danian interval. Whereas the preservation of foraminifera is generally not sufficient for stable isotope studies, well preserved ostracodes provide continuous upper Danian stable isotope records (δ13C, 18O) at Sidi Nasseur, W Tunisia. The late Danian is considered to cover a hyperthermal, known as the “Latest Danian Event” (LDE; ~61.75 Ma) or “Top C27n Event” and has been unequivocally identified in benthic foraminiferal isotopes from shelf sediments in Egypt and deep-sea material from the Pacific Ocean. Stratigraphic changes in the isotope ratios of the genus Bairdia reveal a rather scattered record for δ13C lacking any pronounced negative δ13C excursion, probably due to the many factors influencing δ13C in ostracodes like metabo- lism, diet or dissolved inorganic carbon of sea-water. The accompanying δ18O record is less ambiguous showing a shift towards lower values close to the level where the LDE is to be expected, but minimum values are similar to δ18O values at the base and top of the studied sequence. These data suggest that the core of the negative stable isotope excursions of the LDE is lost in the stratigraphic gap at the planktic foraminiferal P3a/P3b and calcareous nannofossil NTp7A/NTp7B subzonal boundaries, so that the LDE could not be unequivocally identified in Tunisia. A cross-plot of δ13C and δ18O of ostracode valves displays distinctive clusters for smooth-shelled taxa like Bairdia and others as well as for ornamented taxa, with the latter group showing substantially lower values for both δ13C and δ18O. This pattern strongly resembles those from early Eocene data from southwestern France and Recent ostracodes from the Iceland Plateau. The offsets suggest substantial differences in life style, food source or isotope fractionation during the calcification process for different shell morphologies in ostracodes.
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Biotic impact of Eocene thermal maximum 2 in a shelf setting (Dababiya, Egypt).
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The Paleocene-Eocene thermal maximum (PETM) initiated a global biotic event with major evolutionary impacts. Since a series of minor δ13C and δ18O excursions, indicative of hyperthermals, now appears to characterize early Eocene climate, it remains to be investigated how the biosphere responded to these warming events. We studied the Esna Formation at Dababiya (Nile Basin, Egypt), in order to identify Eocene thermal maximum 2 (ETM-2) and to evaluate the foraminiferal and ostracode patterns. The studied interval generally consists of gray-brown marls and shales and is interrupted by a sequence of deviating lithologies, representing an early Eocene Egyptian environmental perturbation that can be linked to ETM-2. The ETM-2 interval consists of brownish shales (bed 1) to marls (bed 2) at the base that grade into a foraminifera-rich chalky limestone (bed 3) at the top. This conspicuous white limestone bed forms the base of the Abu Had Member. A distinct negative δ13C excursion of approximately 1.6‰ is recorded encom- passing this interval and a second negative δ13C shift of 1‰ occurs 5 m higher. These two isotope events are situated respectively in the basal and lower part of the calcareous nannoplankton zone NP11 and appear to correlate with the H1 and H2(?) excursions observed in the deep-sea records. The lower δ13C excursion is associated with benthic foraminiferal and ostracode changes and settlement of impoverished anomalous foraminiferal (planktic and benthic) assemblages, indicating a transient environmental anomaly, disrupting the entire marine ecosystem during ETM-2. Our observations indicate some similarities between the sedimentary and biotic expressions of ETM-2 and the PETM at Dababiya, pointing to similar processes operating in the Egyptian Basin during these global warming events.
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The role of human interference on the channel shifting of the Karkheh River in the Lower Khuzestan plain (Mesopotamia, SW Iran)
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This study is concerned with the Late Holocene floodplain history of the Karkheh River in Lower Khuzestan, and in particular with the role of human action upon its channel shifts. The research was conducted in a multidisciplinary way, in which resources and approaches from different research fields were combined: (1) geomorphological mapping based on the interpretation of Landsat and CORONA satellite imagery, (2) analyses of geological sequences, including the identification of sedimentary facies and radiocarbon dating of organic material, (3) an archaeological field survey of ancient settlements, and (4) consultation of historical documents, mainly Arabic texts from the 9th–14th century and European travel literature from the 16th-early 20th century. Three main channel belts of the Karkheh were identified (labelled Kh1, Kh2 and Kh3), corresponding to successive stages in the evolution of the floodplain. Two river shifts are documented in the datasets, both taking place within the last 2000 years. The first avulsion regards a shift from channel belt Kh1, once a tributary of the Karun, to the straight river bed of Kh2, taking place at least after 1240–1310 cal BP/710–640 AD. The second avulsion, from Kh2 to Kh3, is clearly documented in historical sources and happened in a single night event in the year 1837/113 cal BP. Reactivation of the Kh2 river bed and its irrigation canals can be attributed to the recent construction of an artificial canal bypassing the second avulsion point. Both river shifts were strongly influenced by human interference, whereby an artificial irrigation canal took over the entire river flow from the main channel belt. Most likely, a combination of human-induced factors, such as weakening of the river levees, high sedimentation rates and disadvantageous channel gradients, led to a situation prone to avulsion.
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Geoarchaeological Research in Lower Khuzestan: State of the Art
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Studying the Influence of Landscape Changes on the Late Bronze Age Abandonment of the Harbour Town HST: Unravelling the Sedimentary Record of the Larnaca Salt Lake, Cyprus
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Site Saint-Lambert, à Liège : Datations Carbone 14 par A.M.S. des occupations mésolithiques et néolithiques (secteur DDD et SDT)
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Using Historical Imagery and GIS for Reconstructing the Ancient Landscapes of Khuzestan (SW Iran)
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The role of rivers in ancient societies, or how man transformed the alluvial landscapes of Khuzestan (SW Iran)
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Studying the driving forces of landscape change in the surroundings of the Late Bronze Age harbor town Halla Sultan Tekke, Cyprus
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Intra- and Intertaxon stable O and C isotope variability of fossil fish otoliths: an early Eocene test case
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Knowledge of basic data variability is essential for the interpretation of any proxy-based paleotemperature record. To evaluate this for δ18O stable isotope paleothermometry based on early Paleogene fish otoliths from marginal marine environments, an intra- and interspecific stable O and C isotope study was performed at a single locality in the southern North Sea Basin (Ampe Quarry, Egem, Belgium), where shallow marine sands and silts are exposed. The age of the deposits is early late Ypresian (ca. 50.9 Ma) and falls within the early Eocene climatic optimum (EECO) interval. In each of four fossiliferous levels sampled, the same three otolith species were analyzed (Platycephalus janeti, Paraconger papointi and “genus Neobythitinorum” subregularis). Intrataxon stable isotope spread amounts on average 2.50-3.00‰ for all taxa and is present in all levels. This implies that each sample level comprises substantial variability, which can be attributed to a combination of temporal and taphonomic effects. More importantly, intertaxon offsets of 4.60‰ in δ13C and 2.20‰ in δ18O between the mean values of the three otolith species are found, with “N.” subregularis representing more positive values relative to the other species. We hypothesize that freshwater influence of coastal waters is the most likely cause for these discrepancies. Similar analyses on two coastal bivalve species (Venericardia sulcata and Callista laevigata) corroborate this hypothesis. Accordingly, δ18O values measured on “N.” subregularis otoliths probably represent a more open oce- anic signal, and therefore seem well-suited for δ18O stable isotope paleothermometry. This study highlights the importance of investigating data variability of a biogenic carbonate paleotemperature proxy at the species level, before applying paleotemperature equations and interpreting the outcome.
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