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  • Journal of Quaternary Science
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  • Abstract: The pollen record of three marine late Quaternary cores off Senegal shows a juxtaposition of Mediterranean, Northern Saharan, Central Saharan elements, which are considered transported by the trade winds from a winter-rainfall area, and Sahelian, Soudanese, Soudano-Guinean elements, considered transported both by winds and mostly by the Senegal River, and coming from the monsoonal, summer tropical rainfall area of southern West Africa. Littoral vegetation is either the edaphically dry and saline Chenopodiaceae from sebkhas at the time of the main regression, or the warm tropical humid mangrove with Rhizophora during the humid optimum period. Four stratigraphic zones reflect, from basis to top: Zone 4. A semi-arid period with a balanced pollen input. Zone 3. A very arid period with the disappearance of monsoonal pollen, probably from the disappearance of the Senegal River, a very saline littoral plain with Chenopodiaceae, a larger input of northern Saharan pollen from intensified trade winds. Zone 2. A quite humid period, much more so than today, very suddenly established, with a northward extension of the monsoonal areas, a rich littoral mangrove, and weakening of the trade winds. Zone l. A slow and steady evolution toward the present semi-humid conditions with regression of the mangrove, and of the monsoonal areas toward the south. Tentative datations and correlations with the Tchad area suggested: zone 4: 22,500 to 19,000 years BP; zone 3: 19,000 to 12,500 years BP; zone 2: 12,500 to 5,500 years BP; zone 1: 5,500 years BP to top of core. Dinoflagellate cysts display a tropical assemblage with mostly estuarine neritic elements and also a weak oceanic component, mostly in the lower slope core 47. Cosmopolitan taxa dominate the assemblage and only a few species point to more specialized environments. Quantitative variations of the assemblage are the basis of stratigraphy which is not similar to the pollen stratigraphy, and an inshore-outshore gradient has to be taken into account to correlate the three cores. Category: geoscientificInformation Source: Supplement to: Rossignol-Strick, Martine; Duzer, Daniele (1979): Late Quaternary pollen and dinoflagellate cysts in marine cores off West Africa. Meteor Forschungsergebnisse, Deutsche Forschungsgemeinschaft, Reihe C Geologie und Geophysik, Gebrüder Bornträger, Berlin, Stuttgart, C30, 1-14 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 15.443333 * LONGITUDE: -17.306667 * DATE/TIME: 1971-01-01T00:00:00 * ELEVATION: -625.0 m * LOCATION: East Atlantic * CAMPAIGN: M25 * BASIS: Meteor (1964) * METHOD|DEVICE: Kasten corer EVENT LABEL: * LATITUDE: 15.480000 * LONGITUDE: -17.360000 * DATE/TIME: 1971-11-17T00:00:00 * ELEVATION: -945.0 m * Recovery: 5.5 m * LOCATION: East Atlantic * CAMPAIGN: M25 * BASIS: Meteor (1964) * METHOD|DEVICE: Kasten corer EVENT LABEL: * LATITUDE: 15.825000 * LONGITUDE: -17.861667 * DATE/TIME: 1971-11-17T00:00:00 * ELEVATION: -2576.0 m * Recovery: 6 m * LOCATION: East Atlantic * CAMPAIGN: M25 * BASIS: Meteor (1964) * METHOD|DEVICE: Kasten corer
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  • South Atlantic in Late Quaternary: Reconstruction of Budget and Currents... Late Quaternary water mass variability derived from the pteropod preservation state in sediments of the western South Atlantic Ocean and the Caribbean Sea
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  • South Atlantic in Late Quaternary: Reconstruction of Budget and Currents
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  • Journal of Quaternary Science
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  • Abstract: A model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial-interglacial cycle in the Capricorn Channel, southern Great Barrier Reef (GBR). Stable isotope ratios, grainsize, carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level (mbsl). Results show variations in the flux of terrigenous, neritic and pelagic sediments to the continental slope over the last sea level cycle. During the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl. The percentages of quartz and feldspar in the cores decreased with water depth, while the percentage of clay increased. X-ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the Fitzroy River, which debouched directly into the northwest sector of the Capricorn Channel at this time. The cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite (HMC) during the glacial. The influx of HMC and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial, and also from HMC ooids precipitated at the head of the Capricorn Channel at this time. Mass accumulation rates (MARs) are high (13.5 g/cm**/kyr) during the glacial and peak at ~20 g/cm** 3/kyr in the early transgression (16-14 ka BP). MARs then decline with further sea level rise as the Fitzroy River mouth retreats from the edge of the continental shelf after 13.5 ka BP. MARs remain low (4 g/cm**3/kyr) throughout the Holocene highstand. Data for the Holocene highstand indicate there is a reduction in siliciclastic influx to the Capricorn Channel with little quartz and feldspar below 350 mbsl. However, fine-grained fluvial sediments, presumably from the Fitzroy River, were still accumulating on the mid slope down to 2000 mbsl. The proportion of pelagic calcite in the core tops increases with water depth, while HMC decreases, and is present only in trace amounts in cores below 1500 mbsl. The difference in the percentage of HMC in the deeper cores between the glacial and Holocene may reflect differences in supply or deepening of the HMC lysocline during the glacial. Sediment accumulation rates also vary between cores in the Capricorn Channel and do not show the expected exponential decrease with depth. This may be due to intermediate or deep water currents reworking the sediments. It is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments. Comparison of the Capricorn Channel MARs with those for other mixed carbonate/siliciclastic provinces from the northeast margin of Australia indicates that peak MARs in the early transgression in the Capricorn Channel precede those from the central GBR and south of Fraser Island. The difference in the timing of the carbonate and siliciclastic MAR peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces. The only common trend in the MARs from the northeast margin of Australia is the near synchronicity of the carbonate and siliciclastic MAR peaks in individual sediment cores, which supports a coeval sedimentation model. Category: geoscientificInformation Source: Supplement to: Bostock, Helen C; Opdyke, Bradley N; Gagan, Michael K; Fifield, L Keith (2009): Late Quaternary siliciclastic/carbonate sedimentation model for the Capricorn Channel, southern Great Barrier Reef province, Australia. Marine Geology, 257(1-4), 107-123, https://doi.org/10.1016/j.margeo.2008.11.003 Supplemental Information: Not Availble Coverage: Not Available
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  • cores... core... late... Sediment... Quaternary.
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  • Abstract: Analyses of terrigenous sediments from the Chilean continental slope off the southern border of the Atacama desert (27.5°S), focusing on illite crystallinity and the Fe:Al ratio of the sediments, reveal a high-frequency variability of the position of the Southern Westerlies, which is very similar to the coeval short-term climatic events known from Greenland ice cores and from North Atlantic sediments. Besides showing dominantly precession-driven variability in precipitation over the Andes, these analyses also reveal rapid changes in weathering intensity along the Chilean Coastal Range during the last 80,000 years. These rapid changes occur at much shorter timescales than the 19-100 kyr orbital forcing of the Milankovitch cycles. Category: geoscientificInformation Source: Supplement to: Lamy, Frank; Klump, Jens; Hebbeln, Dierk; Wefer, Gerold (2000): Late Quaternary rapid climate change in northern Chile. Terra Nova, 12, 8-13, https://doi.org/10.1046/j.1365-3121.2000.00265.x Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -27.466667 * LONGITUDE: -71.251667 * DATE/TIME: 1995-06-07T00:00:00 * ELEVATION: -1947.0 m * Recovery: 4.89 m * LOCATION: South-East Pacific * CAMPAIGN: SO102/2 * BASIS: Sonne * METHOD|DEVICE: Gravity corer (Kiel type)
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  • core... late... Quaternary... Bioerosion on late Quaternary planktonic foraminifera related to paleoproductivity in the western South Atlantic... sediment
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  • Abstract: The palaeoclimatic conditions during the Last Glacial Maximum (LGM) of southern South America and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially. Longer palaeoclimatic records covering the Late Quaternary are rare. A particularly sensitive area to Late Quaternary climatic changes is the Norte Chico, northern Chile, because of its extreme climatic gradients. Small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments. To unveil the history of shifting climatic zones in northern Chile, we present a sedimentological study of a marine sediment core (GeoB 3375-1) from the continental slope off the Norte Chico (27.5°S). Sedimentological investigations include bulk- and silt grain-size determinations by sieving, Atterberg separation, and detailed SediGraph analyses. Additionally, clay mineralogical parameters were obtained by X-ray diffraction methods. The 14C-dated core, covering the time span from approximately 10,000 to 120,000 cal. yr B.P., consists of hemipelagic sediments. Terrigenous sedimentological parameters reveal a strong cyclicity, which is interpreted in terms of variations of sediment provenance, modifications of the terrestrial weathering regimes, and modes of sediment input to the ocean. These interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern Chile (27.5°S) through the Late Quaternary. The cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles. For the palaeoclimatic signal, this means that more humid conditions coincide with maxima of the precession index, as e.g. during the LGM. Higher seasonal precipitation for this part of Chile is most likely derived from frontal winter rain of the Southern Westerlies. Thus, the data presented here favour not only an equatorward shift of this atmospheric circulation system during the LGM, but also precession-controlled latitudinal movements throughout the Late Quaternary. Precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the Northern Hemisphere monsoonal system in the Atlantic Ocean region. Category: geoscientificInformation Source: Supplement to: Lamy, Frank; Hebbeln, Dierk; Wefer, Gerold (1998): Late Quaternary precessional cycles of terrigenous sediment input off the Norte Chico, Chile (27.5°S) and paleoclimatic implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 141(3-4), 233-251, https://doi.org/10.1016/S0031-0182(98)90052-9 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -27.466667 * LONGITUDE: -71.251667 * DATE/TIME: 1995-06-07T00:00:00 * ELEVATION: -1947.0 m * Recovery: 4.89 m * LOCATION: South-East Pacific * CAMPAIGN: SO102/2 * BASIS: Sonne * METHOD|DEVICE: Gravity corer (Kiel type)
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