W. Kuhnt

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

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Publications (136)245.35 Total impact

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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.
    Quaternary Science Reviews 03/2015; 112. · 4.57 Impact Factor
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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.
    Biogeosciences 02/2015; 12:1169-1189. · 3.75 Impact Factor
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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.
    Nature Communications 01/2015; 6(5916). · 10.74 Impact Factor
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    ABSTRACT: 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 my To date, the processes driving high-amplitude climate variability and sustaining global warmth during this ...
    Geology. 01/2015;
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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.
    Paleoceanography. 10/2014;
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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.
    Cretaceous Research 09/2014; · 2.39 Impact Factor
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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.
    Geology 01/2014; 42(1):19-22. · 4.64 Impact Factor
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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.
    International Journal of Earth Sciences 12/2013; 103(1). · 2.08 Impact Factor
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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.
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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.
    Paleoceanography. 11/2013;
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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.
    Cretaceous Research 10/2013; 45:288–305. · 2.39 Impact Factor
  • Goldschmidt; 08/2013
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    ABSTRACT: The Turonian to Santonian organic-rich successions deposited in the continuously subsiding Tarfaya Atlantic coastal basin (SW Morocco) allow detailed reconstruction of depositional environments and correlation to eustatic sea level changes. We present high-resolution X-ray fluorescence (XRF) scanning and natural gamma-ray (NGR) records from a newly drilled sedimentary core Tarfaya SN°2 (27° 57´ 43.1´´N, 12° 48´ 37.0´´W), which recovered a continuous sedimentary succession from a middle to outer shelf environment. In the latest Turonian, the late Coniacian, and the middle and latest Santonian, high NGR and Al with low Mn and Ca content indicate pronounced dysoxic horizons that reflect impingement of the oxygen minimum zone on the shelf during sea level highstands. In contrast, lower NGR and Al with higher Mn and Ca values indicate high detrital carbonate content and more oxic conditions related to regressive events in the late Turonian, early to middle Conacian and early Santonian. Exceptionally high sedimentation rates (>10cm/kyr) characterize the late Turonian, and spectral analyses of XRF and NGR data reveal that sedimentation was mostly controlled by obliquity and precession, suggesting an overriding glacioeustatic control. However, the response to orbital forcing weakened during the latest Turonian, when sedimentation rates declined markedly to ~2 cm/kyr. We will extend this study to three newly drilled cores nearby that recovered sediment sequences from the late Albian to late Turonian and from the late Santonian to Campanian in order to retrace the complete Late Cretaceous depositional history of the Tarfaya Basin and to develop a high-resolution carbon isotope stratigraphy allowing correlation to records from other continental margins. Key words: Late Cretaceous, Tarfaya Basin, XRF scanning, natural gamma-ray, oxygen minimum zone, sea level, orbital forcing.
    04/2013;
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    ABSTRACT: We integrate micropaleontological and geochemical records (benthic stable isotopes, neodymium isotopes, benthic foraminiferal abundances and XRF-scanner derived elemental data) from well-dated Pacific Ocean successions (15–12.7 Ma) to monitor circulation changes during the middle Miocene transition into a colder climate mode with permanent Antarctic ice cover. Together with previously published records, our results show improvement in deep water ventilation and strengthening of the meridional overturning circulation following major ice expansion at ∼13.9 Ma. Neodymium isotope data reveal, however, that the provenance of intermediate and deep water masses did not change markedly between 15 and 12.7 Ma. We attribute the increased δ13C gradient between Pacific deep and intermediate water masses between ∼13.6 and 12.7 Ma to more vigorous entrainment of Pacific Central Water into the wind-driven ocean circulation due to enhanced production of intermediate and deep waters in the Southern Ocean. Prominent 100 kyr ventilation cycles after 13.9 Ma reveal that the deep Pacific remained poorly ventilated during warmer intervals at high eccentricity, whereas colder periods (low eccentricity) were characterized by a more vigorous meridional overturning circulation with enhanced carbonate preservation. The long-term δ13C decline in Pacific intermediate and deep water sites between 13.5 and 12.7 Ma reflects a global trend, probably related to a re-adjustment response of the global carbon cycle following the last 400 kyr carbon maximum (CM6) of the “Monterey Excursion”.
    Earth and Planetary Science Letters 03/2013; 365:38–50. · 4.72 Impact Factor
  • 2nd Southeast Asia Gateway Evolution Meeting (SAGE); 03/2013
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    ABSTRACT: New drill cores from the Lower Aptian historical stratotype at Roquefort-La Bédoule (SE France) provide continuous high-resolution geochemical and isotope records which closely track the onset of OAE 1a in a subtropical intra-shelf basin (South Provençal Basin). The drilling operation recovered a total of 180 m of undisturbed sediments in three holes. The lowermost 67 m correspond to the Bedoulian (core LB1) and are here analyzed in high-resolution using geochemical proxies (stable carbon isotopes, stable oxygen isotopes, and carbonate content) and foraminiferal biostratigraphy. Pervasive bioturbation through core LB1 suggests mostly oxygenated bottom water conditions with transient dysoxic episodes, as shown by higher pyrite and glauconite concentrations within the marlstones. Unprecedented resolution over the negative δ13C excursion preceding OAE 1a (segment C3) reveals a characteristic double trough extending over ∼5.5 m in core LB1. This long-lasting negative excursion was possibly linked to multiple pulses of enhanced CO2 release to the atmosphere. Estimated sedimentation rates of 1.6–2 cm/kyr indicate that the negative δ13C excursion lasted >200 kyr, while the main positive carbon isotope shift (segment C4) had a duration of >300 kyr. Fluctuations in δ18O suggest transient episodes of climate warming and cooling at the northern margin of the Tethys or even on a more global scale prior to the onset of OAE 1a.
    Cretaceous Research 02/2013; 39:6–16. · 2.39 Impact Factor
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    ABSTRACT: Using an integrated multidisciplinary approach the upper part of the Lower Cretaceous northeastern Tunisian Jebel Ammar sedimentary succession was examined in detail. The method applied included lithologic and microfacies analyses, micropalaeontology, sedimentology, variations in organic matter (OM) content and carbonate carbon stable isotope (δ13C) record. A major result was the identification in this sector of Tunisia of the Early Aptian (Bedoulian) OAE1a event in a biostratigraphically well-calibrated context, its location keyed to planktonic foraminiferal zones and isotopic stages.The most striking feature to the Jebel Ammar Aptian sequence is the presence of a 25 m interval of black limestones and marly limestones, of which the microfacies shows that these darker beds consist of wackestones with the presence of abundant radiolarians, a fair number of diversified planktonic and relatively rare benthic foraminifers, together an indication of a pelagic palaeoenvironment. The foraminiferal marker Schackoina (Leupoldina) cabri (still very rare at the beginning of its range) first occurs about six metres above the base of this interval, but becomes much more abundant in its uppermost part, together with the radially- elongate-chambered praehedbergellids. This “acme” of S. (L.) cabri is nearly contemporary with a radiolarian bloom. Rock Eval analyses show TOC values up to 4.59% and a Tmax ranging between 441 and 513 °C, which indicates an overmature OM. The δ13C isotope curve shows an evolution similar to those recognized worldwide. The lower part of the darker beds includes a marked shift in isotope values from −2.40 to +3.02 ‰/PDB. This increase is assumed to be equivalent to the isotopic C4 stage of Menegatti et al. (1998, Paleoceanography, 13, 530–545). The signature of the middle and upper part of the isotopic curve is tentatively interpreted as comprising the C5–C7 stages. The first occurrence of S. (L.) cabri is located in the upper part of C4 and its acme as well as the radiolarian bloom is situated within the span of the C7 stage. These results are fairly consistent, though with minor discrepancies, with what has been published from several parts of the North Tethyan margin and more particularly the Lower Aptian type area of southeastern France, where S. (L.) cabri first occurs at the C3/C4 stage boundary with an acme that begins in the lower part of C7.
    Cretaceous Research 02/2013; 39:133–148. · 2.39 Impact Factor
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    ABSTRACT: We present trace element compositions, rare earth elements (REEs) and radiogenic Nd-Sr isotope analyses of Cretaceous to recent sediments of the Tarfaya basin, SW Morocco, in order to identify tectonic setting, source rocks composition and sediments provenance. The results suggest that the sediments originate from heterogeneous source areas of the Reguibat Shield and the Mauritanides (West African Craton), as well as the western Anti-Atlas, which probably form the basement in this area. For interpreting the analyzed trace element results, we assume that elemental ratios such as La/Sc, Th/Sc, Cr/Th, Th/Co, La/Co and Eu/Eu∗ in the detrital silicate fraction of the sedimentary rocks behaved as a closed system during transport and cementation, which is justified by the consistency of all obtained results. The La/Y-Sc/Cr binary and La-Th-Sc ternary relationships suggest that the Tarfaya basin sediments were deposited in a passive margin setting. The trace element ratios of La/Sc, Th/Sc, Cr/Th and Th/Co indicate a felsic source. Moreover, chondrite-normalized REE patterns with light rare earth elements (LREE) enrichment, a flat heavy rare earth elements (HREE) and negative Eu anomalies can also be attributed to a felsic source for the Tarfaya basin sediments. The Nd isotope model ages (TDM=2.0 to 2.2 Ga) of the Early Cretaceous sediments suggest that sediments were derived from the Eburnean terrain (Reguibat Shield). On the other hand, Late Cretaceous to Miocene-Pliocene sediments show younger model ages (TDM=1.8 Ga, on average) indicating an origin from both the Reguibat Shield and the western Anti-Atlas. In contrast, the southernmost studied Sebkha Aridal section (Oligocene to Miocene-Pliocene) yields older provenance ages (TDM=2.5 to 2.6 Ga) indicating that these sediments were dominantly derived from the Archean terrain of the Reguibat Shield.
    Journal of African Earth Sciences 01/2013; · 1.38 Impact Factor
  • American Geophysical Union (AGU), Annual Fall Meeting; 12/2012
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    ABSTRACT: The global carbon cycle during the mid-Cretaceous (˜125-88 million years ago, Ma) experienced numerous major perturbations linked to increased organic carbon burial under widespread, possibly basin-scale oxygen deficiency and episodes of euxinia (anoxic and H2S-containing). The largest of these episodes, the Cenomanian-Turonian boundary event (ca. 93.5 Ma), or oceanic anoxic event (OAE) 2, was marked by pervasive deposition of organic-rich, laminated black shales in deep waters and in some cases across continental shelves. This deposition is recorded in a pronounced positive carbon isotope excursion seen ubiquitously in carbonates and organic matter. Enrichments of redox-sensitive, often bioessential trace metals, including Fe and Mo, indicate major shifts in their biogeochemical cycles under reducing conditions that may be linked to changes in primary production. Iron enrichments and bulk Fe isotope compositions track the sources and sinks of Fe in the proto-North Atlantic at seven localities marked by diverse depositional conditions. Included are an ancestral mid-ocean ridge and euxinic, intermittently euxinic, and oxic settings across varying paleodepths throughout the basin. These data yield evidence for a reactive Fe shuttle that likely delivered Fe from the shallow shelf to the deep ocean basin, as well as (1) hydrothermal sources enhanced by accelerated seafloor spreading or emplacement of large igneous province(s) and (2) local-scale Fe remobilization within the sediment column. This study, the first to explore Fe cycling and enrichment patterns on an ocean scale using iron isotope data, demonstrates the complex processes operating on this scale that can mask simple source-sink relationships. The data imply that the proto-North Atlantic received elevated Fe inputs from several sources (e.g., hydrothermal, shuttle and detrital inputs) and that the redox state of the basin was not exclusively euxinic, suggesting previously unknown heterogeneity in depositional conditions and biogeochemical cycling within those settings during OAE-2.
    Paleoceanography 09/2012; 27(3):3223-. · 3.92 Impact Factor

Publication Stats

2k Citations
245.35 Total Impact Points

Institutions

  • 1996–2015
    • Christian-Albrechts-Universität zu Kiel
      • • Institute of Geosciences
      • • Department of Geosciences
      • • Zoological Institute and Museum
      Kiel, Schleswig-Holstein, Germany
  • 2011
    • Goethe-Universität Frankfurt am Main
      • Institut für Geowissenschaften
      Frankfurt, Hesse, Germany
  • 2007
    • Universität Bremen
      • MARUM - Center for Marine Environmental Sciences
      Bremen, Bremen, Germany
  • 2001
    • Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
      • Division of Geosciences
      Bremerhaven, Bremen, Germany
  • 1994
    • University of Tuebingen
      Tübingen, Baden-Württemberg, Germany