W. Kuhnt

Christian-Albrechts-Universität zu Kiel, Kiel, Schleswig-Holstein, Germany

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Publications (178)261 Total impact

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    ABSTRACT: In 2009 two wells were drilled with 100% core recovery at Roquefort-La Bédoule (Bouches-du-Rhône, SE France), the historical Bedoulian stratotype. Here we present holostratigraphic results based on a detailed study of the cored sediments. Our work confirms that the La Bédoule area offers one of the best records for the period spanning the late Bedoulian, the anoxic event OAE1a and the Bedoulian/Gargasian (lower-upper Aptian substages) transition. New data provide a refined succession of micropaleontogical events already well correlated with ammonites from previous fieldwork and, thus, improve the cross-calibration of bioevents with high-resolution isotope stratigraphy. Methods of the quantitative micropalaeontology applied on benthic foraminifera such as tritaxias help testing their probable orbitally triggered cyclicity, which might be used to precise estimates of duration of events such as OAE1a, the Dufrenoya furcata ammonite Zone, the Globigerinelloides ferreolensis planktonic foraminiferal zone and the C7 isotopic stage.
    Full-text · Article · Dec 2015 · Cretaceous Research
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    ABSTRACT: In 2009 two wells were drilled with 100% core recovery at Roquefort-La Bédoule (Bouches-du-Rhône, SE France), the historical Bedoulian stratotype. Here we present holostratigraphic results based on a detailed study of the cored sediments. Our work confirms that the La Bédoule area offers one of the best records for the period spanning the late Bedoulian, the anoxic event OAE1a and the Bedoulian/Gargasian (lower-upper Aptian substages) transition. New data provide a refined succession of micropaleontogical events already well correlated with ammonites from previous fieldwork and, thus, improve the cross-calibration of bioevents with high-resolution isotope stratigraphy. Methods of the quantitative micropalaeontology applied on benthic foraminifera such as tritaxias help testing their probable orbitally triggered cyclicity, which might be used to precise estimates of duration of events such as OAE1a, the Dufrenoya furcata ammonite Zone, the Globigerinelloides ferreolensis planktonic foraminiferal zone and the C7 isotopic stage.
    No preview · Article · Dec 2015 · Cretaceous Research
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    ABSTRACT: We present core top Mg/Ca, Sr/Ca and δ18O measurements for Cibicidoides wuellerstorfi and Hoeglundina elegans from the Timor Sea and the Makassar Strait, which span a bottom water temperature (BWT) range from 2 to 18 °C. In both species Mg/Ca ratios are positively and significantly correlated with BWT, while δ18O measurements are significantly anti-correlated with BWT. Comparison of calcification temperatures derived from Mg/Ca ratios and δ18O measurements yield comparable results and closely match CTD-measured temperatures. We integrate our results with previously published data sets from the Atlantic, Indian and Pacific Oceans and provide temperature calibration equations over the temperature range from 2 to 12 °C for H. elegans and from 0 to 10 °C for C. wuellerstorfi. We found geographical differences in the relation of benthic Mg/Ca ratios to BWT: C. wuellerstorfi shows Mg/Ca sensitivity to BWT of 19% increase in Mg/Ca per °C for the Atlantic Ocean and of 15% per °C for the Indian and Pacific Oceans. H. elegans shows Mg/Ca sensitivity to BWT of 16% increase in Mg/Ca per °C for the Atlantic Ocean and of 14% per °C for the Indian and Pacific Oceans. C. wuellerstorfi Sr/Ca variability appears to be mainly driven by carbonate ion saturation, whereas H. elegans Sr/Ca variability is closely linked to BWT in the compiled data sets from the Atlantic, Indian and Pacific Oceans.
    Full-text · Article · Oct 2015 · Marine Micropaleontology
  • Y. Bian · J. Li · Z. Jian · F. Chu · Z. Chu · W. Kuhnt · L. Ye
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    ABSTRACT: The environment and climate information during the Holocene is indispensable data for the global climate modeling and forecasting. Scenarios of regional vegetation and climate changes around the Celebes Sea during the Holocene are explored based on the alynological and oxygen isotope records of core MD98-2178 (3.6200°N, 118.7000°E; 1 984 m water depth) from the northwest Celebes Sea in this study. Sea-level changes are discussed since the marine pollen record of core MD98-2178 is considered as an indicator. The sharp decline in concentration of all pollen groups during the Early Holocene, ~10-7 ka BP, indicates a sea-level rise. All pollen groups at 7-4 ka BP suggest sustaining of a high sea-level. The marine pollen record after 4 ka BP shows a slight fall of sea-level. The significant increase in pollen percentage of the tropical montane forest during the Middle Holocene, 5-4 ka BP, suggests a much cold condition along the Celebes Sea at the time. It is suggested that precipitation along the Celebes Sea has been affected by variations of land-ocean distribution and solar activities. It is implied by fluctuation in fern spores record that precipitation was at a high level during the Early Holocene, but lowered after the Middle Holocene, which is in a similar pattern as indicated by the Indonesian stalagmite records.
    No preview · Article · May 2015 · Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences
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    ABSTRACT: International Ocean Discovery Program (IODP) Expedition 353 (29 November 2014-29 January 2015) drilled six sites in the Bay of Bengal, recovering 4280 m of sediments during 32.9 days of on-site drilling. Recovery averaged 97%, including coring with the advanced piston corer, half-length advanced piston corer, and extended core barrel systems. The primary objective of Expedition 353 is to reconstruct changes in Indian monsoon circulation since the Miocene at tectonic to centennial timescales. Analysis of the sediment sections recovered will improve our understanding of how monsoonal climates respond to changes in forcing external to the Earth's climate system (i.e., insolation) and changes in forcing internal to the Earth's climate system, including changes in continental ice volume, greenhouse gases, sea level, and the ocean-atmosphere exchange of energy and moisture. All of these mechanisms play critical roles in current and future climate change in monsoonal regions. The primary signal targeted is the exceptionally low salinity surface waters that result, in roughly equal measure, from both direct summer monsoon precipitation to the Bay of Bengal and runoff from the numerous large river basins that drain into the Bay of Bengal. Changes in rainfall and surface ocean salinity are captured and preserved in a number of chemical, physical, isotopic, and biological components of sediments deposited in the Bay of Bengal. Expedition 353 sites are strategically located in key regions where these signals are the strongest and best preserved. Salinity changes at IODP Sites U1445 and U1446 (northeast Indian margin) result from direct precipitation as well as runoff from the Ganges-Brahmaputra river complex and the many river basins of peninsular India. Salinity changes at IODP Sites U1447 and U1448 (Andaman Sea) result from direct precipitation and runoff from the Irrawaddy and Sal-ween river basins. IODP Site U1443 (Ninetyeast Ridge) is an open-ocean site with a modern surface water salinity very near the global mean but is documented to have recorded changes in monsoonal circulation over orbital to tectonic timescales. This site serves as an anchor for establishing the extent to which the north to south (19°N to 5°N) salinity gradient changes over time.
    Full-text · Article · Apr 2015 · Integrated Ocean Drilling Program: Preliminary Reports
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    Full-text · Book · Apr 2015
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    ABSTRACT: The Indonesian Throughflow (ITF) connects the western Pacific Ocean with the eastern Indian Ocean, thus forming one of the major near surface current systems of the global thermohaline circulation. The intensity of the ITF has been found to be sensitive to changes in global ocean circulation, fluctuations in sea level, as well as to the prevailing monsoonal conditions of the Indonesian Archipelago and NW Australia. This study presents the first reconstruction of ITF dynamics combining radiogenic isotope compositions of neodymium (Nd), strontium (Sr), and lead (Pb) of the clay-size detrital fraction to investigate changes in sediment provenance, and paleo seawater Nd signatures extracted from the planktonic foraminifera and authigenic Fe–Mn oxyhydroxide coatings of the marine sediments focussing on marine isotope stage 3 (MIS3). Sediment core MD01-2378 was recovered within the framework of the International Marine Global Change Study (IMAGES) and is located in the area of the ITF outflow in the western Timor Sea (Scott Plateau, 13° 04.95′ S and 121° 47.27′ E, 1783 m water depth). In order to produce reliable seawater signatures, several extraction methods were tested against each other. The results of the study show that at this core location the extraction of surface water Nd isotope compositions from planktonic foraminifera is complicated by incomplete removal of contributions from Fe–Mn oxyhydroxides carrying ambient bottom water signatures. The bottom water Nd isotope signatures reliably obtained from the sediment coatings (average εNd = −5.0) document an essentially invariable water mass composition similar to today throughout the entire MIS3. The radiogenic Nd, Sr, and Pb isotope records of the clay-sized detrital fraction suggest that the Indonesian Archipelago rather than NW Australia was the main particle source at the location of core MD01-2378, and thus indicating a persistently strong ITF during MIS3. Furthermore, the variations of the detrital radiogenic isotopes are shown to be more sensitive to changes in circulation and document a somewhat enhanced ITF intensity during the early part of MIS3 until 47.4 ka compared with the remaining MIS3.
    No preview · Article · Mar 2015 · Quaternary Science Reviews
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    ABSTRACT: Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation , and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimen-tary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenoma-nian OAE 2 from the northwest African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of < 7 µmol kg −1 under the Peruvian upwelling and < 5 µmol kg −1 in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 µmol kg −1. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 µmol kg −1 , which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm −2 kyr −1 in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 µmol kg −1. Sediments deposited at > 10 µmol kg −1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diage-nesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.
    Full-text · Article · Feb 2015 · Biogeosciences
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    ABSTRACT: The Miocene Climatic Optimum (MCO; ca. 17-14.7 Ma) represents one of several major interruptions in the long-term cooling trend of the past 50 m.y. To date, the processes driving high-amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic. We present high-resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional, continuous, carbonate-rich sedimentary archive (Integrated Ocean Drilling Program Site U1337, eastern equatorial Pacific Ocean), which offer a new view of climate evolution over the onset of the MCO. A sharp decline in δ18O and δ13C at ca. 16.9 Ma, contemporaneous with a massive increase in carbonate dissolution, demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle. The rapid recovery in δ13C at ca. 16.7 Ma, ~;250 k.y. after the beginning of the MCO, marks the onset of the first carbon isotope maximum within the long-lasting "Monterey Excursion." These results lend support to the notion that atmospheric pCO2 variations drove profound changes in the global carbon reservoir through the MCO, implying a delicate balance between changing CO2 fluxes, rates of silicate weathering, and global carbon sequestration. Comparison with a high-resolution δ13C record spanning the onset of the Cretaceous Oceanic Anoxic Event 1a (~120 m.y. ago) reveals common forcing factors and climatic responses, providing a long-term perspective to understand climate-carbon cycle feedbacks during warmer periods of Earth's climate with markedly different atmospheric CO2 concentrations.
    No preview · Article · Feb 2015 · Geology
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    ABSTRACT: The evolution of the Australian monsoon in relation to high-latitude temperature fluctuations over the last termination remains highly enigmatic. Here we integrate high-resolution riverine runoff and dust proxy data from X-ray fluorescence scanner measurements in four well-dated sediment cores, forming a NE-SW transect across the Timor Sea. Our records reveal that the development of the Australian monsoon closely followed the deglacial warming history of Antarctica. A minimum in riverine runoff documents dry conditions throughout the region during the Antarctic Cold Reversal (15-12.9 ka). Massive intensification of the monsoon coincided with Southern Hemisphere warming and intensified greenhouse forcing over Australia during the atmospheric CO2 rise at 12.9-10 ka. We relate the earlier onset of the monsoon in the Timor Strait (13.4 ka) to regional changes in landmass exposure during deglacial sea-level rise. A return to dryer conditions occurred between 8.1 and 7.3 ka following the early Holocene runoff maximum.
    No preview · Article · Jan 2015 · Nature Communications
  • Y. Bian · J. Li · F. Chu · X. Han · Z. Jian · Z. Chu · W. Kuhnt
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    ABSTRACT: The palynological analysis of two marine core, MD06-3075 (6.4762°N, 125.8322°E; 1878 m water depth, 30.76 m in length) in the southern Philippines and MD98-2178 (3.6200°N, 118.7000°E; 1984 m water depth, 35.6 m in length) in the northwest Celebes Sea, the detailed oxygen isotope records, and other marine pollen records in the west Pacific, provide the regional vegetation and climate history during the Holocene. The record shows that, during the early Holocene, ∼10.0-6 kyr B.P., the pollen percentage of the tropical montane forest decline, suggestting that the tropical montane forest distribute at the high altitude just like nowdays, which indicates a warm condition. The pollen from mangrove group is abundant, presenting the well-development of the mangrove along the coast of the adjacent islands. Meanwhile, the pollen from the herb is rare, but the value of the pteridophyte is much high, indicating a wet condition. During the mid-Holocene, the pollen percentage of the tropical mid-upper montane rainforest is very high at 6-5 kyr B.P, suggesting the downslope movement of the tropical montane forest, indicating a much cold condition at the time. Besides, it is a striking decline in mangrove pollen and a slight less abundance of the fern spore, indicating the vegetation group of mangrove and fern were suppressed during the mid-Holocene. During the late Holocene, a relatively high level of the herbaceous group provides a more open environment. These changes, are relatively the same as stalagmite record in this area, but different from palaeooceanographic records. This likely indicates that tropical vegetation changes have close relationship with the global monsoon.
    No preview · Article · Nov 2014
  • Y. Bian · J. Li · F. Chu · X. Han · Z. Jian · Z. Chu · W. Kuhnt
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    ABSTRACT: The palynological analysis of two marine core, MD06-3075 (6.4762°N, 125.8322°E; 1878 m water depth, 30.76 m in length) in the southern Philippines and MD98-2178 (3.6200°N, 118.7000°E; 1984 m water depth, 35.6 m in length) in the northwest Celebes Sea, the detailed oxygen isotope records, and other marine pollen records in the west Pacific, provide the regional vegetation and climate history during the Holocene. The record shows that, during the early Holocene, ∼10.0-6 kyr B.P., the pollen percentage of the tropical montane forest decline, suggestting that the tropical montane forest distribute at the high altitude just like nowdays, which indicates a warm condition. The pollen from mangrove group is abundant, presenting the well-development of the mangrove along the coast of the adjacent islands. Meanwhile, the pollen from the herb is rare, but the value of the pteridophyte is much high, indicating a wet condition. During the mid-Holocene, the pollen percentage of the tropical mid-upper montane rainforest is very high at 6-5 kyr B.P, suggesting the downslope movement of the tropical montane forest, indicating a much cold condition at the time. Besides, it is a striking decline in mangrove pollen and a slight less abundance of the fern spore, indicating the vegetation group of mangrove and fern were suppressed during the mid-Holocene. During the late Holocene, a relatively high level of the herbaceous group provides a more open environment. These changes, are relatively the same as stalagmite record in this area, but different from palaeooceanographic records. This likely indicates that tropical vegetation changes have close relationship with the global monsoon.
    No preview · Article · Nov 2014
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    ABSTRACT: Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking the terrestrial and marine realms. We present high-resolution stable isotope, UK’37 sea-surface temperature, X-ray fluorescence (XRF) core scanning and coccolithophore-derived paleoproductivity records covering the past 120 ka from International Marine Global Change (IMAGES) Program Core MD06-3075 (6°29' N, 125°50' E, water depth 1878 m), situated in the Davao Gulf on the southern side of Mindanao. XRF-derived log(Fe/Ca) records provide a robust proxy for runoff-driven sedimentary discharge from Mindanao, whilst past changes in local productivity are associated with variable freshwater runoff and stratification of the surface layer. Significant precessional-scale variability in sedimentary discharge occurred during Marine Isotope Stage (MIS) 5, with peaks in discharge contemporaneous with Northern Hemisphere summer insolation minima. We attribute these changes to the latitudinal migration of the Intertropical Convergence Zone (ITCZ) over the WPWP together with variability in the strength of the Walker circulation acting on precessional timescales. Between 60 and 15 ka sedimentary discharge at Mindanao was muted, displaying little orbital- or millennial-scale variability, likely in response to weakened precessional insolation forcing and lower sea level driving increased subsidence of air masses over the exposed Sunda Shelf. These results highlight the high degree of local variability in the precipitation response to past climate changes in the WPWP.
    No preview · Article · Nov 2014
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    ABSTRACT: Present day oceans are generally well ventilated except mid-depth oxygen minimum zones (OMZs) under high surface water productivity regimes, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or even anoxic. In particular the Cretaceous Ocean Anoxic Events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossil assemblages preserved in the sedimentary record. Yet both, qualitative and quantitative assessments of intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life are well known. Their implications for constraining past bottom-water oxygenation are addressed in this review, with emphasis on comparing OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the Atlantic NW African shelf. Holocene laminated sediments were encountered at bottom-water oxygen levels of
    No preview · Article · Sep 2014 · Biogeosciences Discussions
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    ABSTRACT: Based on the lithology assemblage, microfacies, and physical and chemical proxies, we reconstruct the relative sea-level curve of late Turonian-early Coniacian in Tethyan Himalaya. Spectral analysis indicates that fourth order sea-level changes were linked to the astronomically stable 405-kyr eccentricity cycle. By comparing with classic global sea-level curves, we suggest that late Turonian-early Coniacian sea-level changes in the southeastern Tethyan margin were controlled by eustasy. Two rapid and significant regressions during late Turonian, which are recorded in different continents, may be interpreted as the result of continental ice expansion, giving some support to the notion that ephemeral polar ice sheets existed even in the super-greenhouse world.
    Full-text · Article · Sep 2014 · Cretaceous Research
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    ABSTRACT: During the Middle Miocene, Earth’s climate transitioned from a relatively warm phase (Miocene climatic optimum) to a colder mode with reestablishment of permanent ice sheets on Antarctica, thus marking a fundamental step in Cenozoic cooling. Carbon sequestration and atmospheric CO2 drawdown through increased terrestrial and/or marine productivity have been proposed as the main drivers of this fundamental transition. We integrate high-resolution (1–3 k.y.) benthic stable isotope data with X-ray fl uorescence scanner– derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive, recovered at Integrated Ocean Drilling Program Site U1338, to reconstruct eastern equatorial Pacifi c productivity variations and to investigate temporal links between high- and low-latitude climate change over the interval 16–13 Ma. Our records show that the climatic optimum (16.8–14.7 Ma) was characterized by high-amplitude climate variations, marked by intense perturbations of the carbon cycle. Episodes of peak warmth at (Southern Hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica ca. 13.8 Ma. We fi nd that two massive increases in opal accumulation ca. 14.0 and ca. 13.8 Ma occurred just before and during the final and most prominent cooling step, supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial Pacific contributed to CO2 drawdown.
    Full-text · Article · Jan 2014 · Geology
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    ABSTRACT: The petrography, heavy mineral analysis, major element geochemical compositions and mineral chemistry of Early Cretaceous to Miocene-Pliocene rocks, and recent sediments of the Tarfaya basin, SW Morocco, have been studied to reveal their depositional tectonic setting, weathering history, and provenance. Bulk sediment compositional and mineral chemical data suggest that these rocks were derived from heterogeneous sources in the Reguibat Shield (West African Craton) including the Mauritanides and the western Anti-Atlas, which likely form the basement in this area. The Early Cretaceous sandstones are subarkosic in composition, while the Miocene-Pliocene sandstones and the recent sediments from Wadis are generally carbonate-rich feldspathic or lithic arenites, which is also reflected in their major element geochemical compositions. The studied samples are characterized by moderate SiO2 contents and variable abundances of Al2O3, K2O, Na2O, and ferromagnesian elements. Binary tectonic discrimination diagrams demonstrate that most samples can be characterized as passive continental marginal deposits. Al2O3/Na2O ratios indicate more intense chemical weathering during the Early Cretaceous and a variable intensity of weathering during the Late Cretaceous, Early Eocene, Oligocene-Early Miocene, Miocene-Pliocene and recent times. Moreover, weathered marls of the Late Cretaceous and Miocene-Pliocene horizons also exhibit relatively low but variable intensity of chemical weathering. Our results indicate that siliciclastics of the Early Cretaceous were primarily derived from the Reguibat Shield and the Mauritanides, in the SW of the basin, whereas those of the Miocene-Pliocene had varying sources that probably included western Anti-Atlas (NE part of the basin) in addition to the Reguibat Shield and the Mauritanides.
    Full-text · Article · Dec 2013 · International Journal of Earth Sciences
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    ABSTRACT: [1] We present high-resolution (2–3 kyr) benthic foraminiferal stable isotopes in a continuous, well-preserved sedimentary archive from the West Pacific Ocean (Ocean Drilling Program Site 1146), which track climate evolution in unprecedented resolution over the period 12.9 to 8.4 Ma. We developed an astronomically tuned chronology over this interval and integrated our new records with published isotope data from the same location to reconstruct long-term climate and ocean circulation development between 16.4 and 8.4 Ma. This extended perspective reveals that the long eccentricity (400 kyr) cycle is prominently encoded in the δ13C signal over most of the record, reflecting long-term fluctuations in the carbon cycle. The δ18O signal closely follows variations in short eccentricity (100 kyr) and obliquity (41 kyr). In particular, the obliquity cycle is prominent from ~14.6 to 14.1 Ma and from ~9.8 to 9.2 Ma, when high-amplitude variability in obliquity is congruent with low-amplitude variability in short eccentricity. The δ18O curve is additionally characterized by a series of incremental steps at ~14.6, 13.9, 13.1, 10.6, 9.9, and 9.0 Ma, which we attribute to progressive deep water cooling and/or glaciation episodes following the end of the Miocene climatic optimum. On the basis of δ18O amplitudes, we find that climate variability decreased substantially after ~13 Ma, except for a remarkable warming episode at ~10.8–10.7 Ma at peak insolation during eccentricity maxima (100 and 400 kyr). This transient warming, associated with a massive negative carbon isotope shift, is reminiscent of intense global warming events at eccentricity maxima during the Miocene climatic optimum.
    No preview · Article · Dec 2013
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    ABSTRACT: During the Middle Miocene, Earth’s climate transitioned from a relatively warm phase (Miocene climatic optimum) to a colder mode with reestablishment of permanent ice sheets on Antarctica, thus marking a fundamental step in Cenozoic cooling. Carbon sequestration and atmospheric CO2 drawdown through increased terrestrial and/or marine productivity have been proposed as the main drivers of this fundamental transition. We integrate high-resolution (1–3 k.y.) benthic stable isotope data with X-ray fluorescence scanner– derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive, recovered at Integrated Ocean Drilling Program Site U1338, to reconstruct eastern equatorial Pacific productivity variations and to investigate temporal links between high- and low-latitude climate change over the interval 16–13 Ma. Our records show that the climatic optimum (16.8–14.7 Ma) was characterized by high-amplitude climate variations, marked by intense perturbations of the carbon cycle. Episodes of peak warmth at (Southern Hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica ca. 13.8 Ma. We find that two massive increases in opal accumulation ca. 14.0 and ca. 13.8 Ma occurred just before and during the final and most prominent cooling step, supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial Pacific contributed to CO2 drawdown.
    Full-text · Dataset · Nov 2013
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    ABSTRACT: Lithological evidence, benthic foraminiferal census counts, and X-ray fluorescence (XRF) scanner-derived elemental data were integrated with planktonic foraminiferal biostratigraphy and bulk carbonate stable isotopes to retrace the Turonian to early Campanian paleoenvironmental evolution and sea-level history of the Tarfaya Atlantic coastal basin (SW Morocco). The lower Turonian is characterized by laminated organic-rich deposits, which contain impoverished benthic foraminiferal assemblages, reflecting impingement of the oxygen minimum zone on the shelf during a sea-level highstand. This highstand level is correlated to the global transgressive pulse above the sequence boundary Tu1. The appearance of low-oxygen tolerant benthic foraminiferal assemblages dominated by Gavelinella sp. in the middle to upper Turonian indicates an improvement in bottom water oxygenation, probably linked to offshore retraction of the oxygen minimum zone during a regressive phase. This interval is marked by major regressive events expressed by a series of erosional truncations associated with the prominent sequence boundaries Tu3 and/or Tu4. Dysoxic–anoxic conditions recorded in the upper Santonian of the Tarfaya Basin coincide with the eustatic sea-level rise prior to Sa3 sequence boundary. The lower Campanian transgression, only recorded in the southern part of the Tarfaya Basin, coincided with substantial deepening, enhanced accumulation of fine-grained clay-rich hemipelagic sediments and improved oxygenation at the seafloor (highest diversity and abundance of benthic foraminiferal assemblages). Stable isotope data from bulk carbonates are tentatively correlated to the English Chalk carbon isotope reference curve, in particular the Hitch Wood Event in the upper Turonian, the Navigation Event in the lower Coniacian, the Horseshoe Bay Event in the Santonian and the Santonian/Campanian Boundary Event.
    Full-text · Article · Oct 2013 · Cretaceous Research

Publication Stats

3k Citations
261.00 Total Impact Points

Institutions

  • 1995-2015
    • Christian-Albrechts-Universität zu Kiel
      • • Institute of Geosciences
      • • Department of Geosciences
      • • Zoological Institute and Museum
      Kiel, Schleswig-Holstein, Germany
  • 2001
    • Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
      • Division of Geosciences
      Bremerhaven, Bremen, Germany
  • 1992-1994
    • University of Tuebingen
      Tübingen, Baden-Württemberg, Germany