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  • 1
    Publication Date: 2015-04-23
    Description: Subsurface fluid flow in oceans and lakes affect bathymetric morphology, sediment distribution and water composition. We present newly discovered giant lacustrine pockmarks in Lake Neuchâtel (up to 160 m diameter and 30 m deep), that rank among the largest known pockmarks in lakes. Our multidisciplinary study reveals ~ 60 m of suspended sediment inside a pockmark. The sediment suspension is 2.6° warmer and isotopically lighter in δ 18 O H2O by 1.5 ‰ than the ambient lake water, documenting currently active fluid flow by karstic groundwater discharge from the Jura Mountain front into the Swiss Plateau hydrological system. Strikingly, the levees of the pockmarks comprise subsurface sediment mobilization deposits representing episodic phases of sediment expulsion during the past. They strongly resemble subsurface fluid flow features in the marine realm. Comparable processes are expected to also be relevant for other carbonate-dominated mountain front ranges, where karstic groundwater discharges into lacustrine or marine settings.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2012-10-14
    Description: The Alpine Triassic units of Switzerland, Northern Italy and Western Austria offer an extensive geological archive, in which the enigmatic process of dolomite formation can be studied in a palaeoenvironmental context. Recent studies clearly demonstrate that large amounts of the Alpine Triassic dolomites are late diagenetic or hydrothermal. Nevertheless, as part of multiple generations of diagenetic overprint, some generations of fine-crystalline, Ca-rich dolomite appear strictly confined to their depositional facies and show signs of very early formation at surface temperatures in specific ancient depositional environments. In this review, three cases of Alpine Triassic dolomites are discussed, where dolomite rocks may have formed during or soon after sedimentation. The sedimentary facies indicate contrasting palaeoenvironmental conditions and, hence, document three different possible processes of dolomite formation: (1) In the Dolomite Mountains (Northern Italy), dolomite beds of the partly isolated Middle Triassic (Anisian/Ladinian) Latemar Platform are confined to the very top of shallowing-upward lagoonal facies cycles. (2) Dolomite beds of the San Giorgio Basin (Southern Switzerland), an intra-platform basin that opened during the Anisian/Ladinian transition, are associated with organic carbon-rich shales, which were deposited in a deeper water environment under anoxic conditions. (3) In the entirely dolomitised platform facies of the Dolomia Principale (Hauptdolomite Formation), a very early generation of fine-crystalline dolomite occurs in the shallowest part of evaporative peritidal cycles. This platform extended over thousands of square kilometres along the Tethys margin during the Late Triassic (Carnian and Norian), and large amounts of carbonate were deposited under hypersaline sabkha-like conditions. Representing three distinct depositional environments, these three different Triassic systems show features in common with several dolomitisation models developed from the study of modern dolomite-forming environments, for example, the sabkha model, the evaporative lagoon/lake model, the organogenic model and the microbial model. Although these actualistic models may be applicable, to reconstruct the palaeoenvironmental conditions during dolomite formation, dolomite-forming processes during the Triassic were apparently quite different from the modern world in terms of distribution and scale. Recent developments in stable isotope geochemistry and high resolution geochemical probing offer the possibility to make better reconstructions of Triassic palaeoceanographic conditions and suggest a non-actualistic approach to better understand dolomite formation during the Triassic.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 3
    Publication Date: 2012-04-15
    Description: We performed a detailed study on the carbon build-up over the 140-year-long chronosequence of the Damma glacier forefield, Switzerland, to gain insights into the organic carbon dynamics during the initial stage of soil formation and ecosystem development. We determined soil carbon and nitrogen contents and their stable isotopic compositions, as well as molecular-level composition of the bulk soils, and recalcitrance parameters of carbon in different fractions. The chronosequence was divided into three age groups, separated by small end moraines that resulted from two glacier re-advances. The net ecosystem carbon balance (NECB) showed an exponential increase over the last decades, with mean annual values that range from 100 g C m −2  yr −1 in the youngest part to over 300 g C m −2  yr −1 in a 60–80 years old part. However, over the entire 140-year chronosequence, the NECB is only 20 g C m −2  yr −1 , similar to results of other glacier forefield studies. The difference between the short- and long-term NECB appears to be caused by reductions in ecosystem carbon (EC) accumulation during periods with a colder climate. We propose that two complementary mechanisms have been responsible: 1) Reductions in net primary productivity down to 50% below the long-term mean, which we estimated using reconstructed effective temperature sums. 2) Disturbance of sites near the terminus of the re-advanced glacier front. Stabilization of soil organic matter appeared to play only a minor role in the coarse-grained forefield. We conclude that the forefield ecosystem, especially primary productivity, reacts rapidly to climate changes. The EC gained at warm periods is easily lost again in a cooling climate. Our conclusions may also be valid for other high mountain ecosystems and possibly arctic ecosystems.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 4
    Publication Date: 2019
    Description: Abstract This paper investigates the hydrothermal fluid circulation that was linked to the extensional evolution of the Adriatic rifted margin during the Jurassic opening of the Alpine Tethys. Remnants of this rifted margin are spectacularly preserved in SE Switzerland and N Italy. Five study areas were chosen ranging from the former proximal to the most distal part of the margin. We demonstrate an intimate link between Jurassic extensional tectonics and fluid activity affecting the pre‐ to early post‐rift sedimentary sequences. Nature, composition and origin of fluids are constrained by a multidisciplinary approach based on field observations and including geochemical (O‐C, Sr, He isotopes, U‐Pb datings, fluid inclusion microthermometry) and petrological methods. Several fluid‐related diagenetic products and processes such as dolomitization, veining, hydraulic brecciation, and silicification can be recognized. It appears that different paleogeographic settings and different stratigraphic levels document distinct phases of fluid activity. The fluids reached temperatures of up to 150°C near paleo‐seafloor. They were enriched in 18O, had high 87Sr/86Sr and low 3He/4He ratios, documenting a strong interaction between seawater and a granitic basement. Many lines of evidence point to the occurrence of over‐pressured fluids and long‐lasting fluid circulation due to fault‐valve mechanisms and high thermal gradients. Two main stages with different fluid chemistry can be recognized: (1) a carbonate‐rich stage that developed during the stretching phases and was linked to high‐angle normal faulting, and (2) a silica‐rich stage occurring during late rift exhumation of crustal and mantle rocks in the distal domains in the presence of detachment faults and high thermal gradients. This paper provides, for the first time, a large and robust characterization of fluid–rock interactions occurring during rifting along an almost complete section across a magma‐poor rifted margin.
    Print ISSN: 0950-091X
    Electronic ISSN: 1365-2117
    Topics: Geosciences
    Published by Wiley
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  • 5
    Publication Date: 2012-01-21
    Description: We established a new high-resolution carbonate carbon isotope record of the Albian interval of the Marne a Fucoidi Formation (Central Apennines, Italy), which was deposited on the southern margin of the western Tethys Ocean. Bulk carbonate sampled with 10–15 cm spacing was used for the construction of a continuous carbon isotope curve through the Albian stage. Spectral analyses reveal prominent 400 kyr cyclicity in the δ13C curve, which correlates with Milankovitch long eccentricity changes. Cycles occurring in our record resemble those observed in several Cenozoic δ13C records, suggesting that a link between orbital forcing and carbon cycling existed also under mid-Cretaceous greenhouse conditions. Based on comparisons with Cenozoic eccentricity-carbon cycle links we hypothesize that 400 kyr cycles in the mid-Cretaceous were related to a fluctuating monsoonal regime, coupled with an unstable oceanic structure, which made the oceanic carbon reservoir sensitive to orbital variations. In the Tethys these oceanographic conditions lasted until the Late Albian, and then were replaced by a more stable circulation mode, less sensitive to orbital forcing.
    Print ISSN: 0883-8305
    Electronic ISSN: 1944-9186
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2012-01-29
    Description: We performed a detailed study on the carbon build-up over the 140 year long chronosequence of the Damma glacier forefield, Switzerland, to gain insights in the organic carbon dynamics during the initial stage of soil formation and ecosystem development. We determined soil carbon and nitrogen contents and their stable isotopic compositions, as well as molecular-level composition of the bulk soils, and recalcitrance parameters of carbon in different fractions. The chronosequence was divided into three age groups, separated by small end moraines that resulted from two glacier re-advances. The net ecosystem carbon balance (NECB) showed an exponential increase over the last decades, with mean annual values that range from 100 g C m −2 yr −1 in the youngest part to over 300 g C m −2 yr −1 in a 60-80 year old part. However, over the entire 140 year chronosequence the NECB is only 20 g C m −2 yr −1 , similar to results of other glacier forefield studies. The difference between the short and long term NECB appears to be caused by reductions in ecosystem carbon accumulation during periods with a colder climate. We propose that two complementary mechanisms have been responsible: 1) Reductions of net primary productivity (NPP) down to 50% below the long term mean, which we estimated using reconstructed effective temperature sums. 2) Disturbance of sites near the terminus of the re-advanced glacier front. Stabilization of soil organic matter appeared to play only a minor role in the coarse-grained forefield. We conclude that the forefield ecosystem, especially primary productivity, reacts rapidly to climate changes. Ecosystem carbon gained at warm periods is easily lost again in a cooling climate. Our conclusions may also be valid for other high mountain ecosystems and possibly arctic ecosystems.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 7
    Publication Date: 2019
    Description: Abstract This study identifies temporal biases in the radiocarbon ages of the planktonic foraminifera species Globigerina bulloides and Globigerinoides ruber (white) in a sediment core from the SW Iberian margin (so‐called Shackleton site). Leaching of the outer shell and measurement of the radiocarbon content of both the leachate and leached sample enabled us to identify surface contamination of the tests and its impact on their 14C ages. Incorporation of younger radiocarbon on the outer shell affected both species and had a larger impact downcore. Interspecies comparison of the 14C ages of the leached samples reveal systematic offsets with 14C ages for G. ruber being younger than G. bulloides ages during the last deglaciation and part of the Early and mid‐Holocene. The greatest offsets (up to 1,030 years) were found during Heinrich Stadial 1, the Younger Dryas, and part of the Holocene. The potential factors differentially affecting these two planktonic species were assessed by complementary 14C, oxygen and carbon isotopes, and species abundance determinations. The coupled effect of bioturbation with changes in the abundance of G. ruber is invoked to account for the large age offsets. Our results highlight that 14C ages of planktonic foraminifera might be largely compromised even in settings characterized by high sediment accumulation rates. Thus, a careful assessment of potential temporal biases must be performed prior to using 14C ages for paleoclimate investigations or radiocarbon calibrations (e.g., marine calibration curve Marine13, Reimer et al., 2013, https://doi.org/10.2458/azu_js_rc.55.16947).
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2012-05-22
    Description: Environmental Science & Technology DOI: 10.1021/es300311h
    Print ISSN: 0013-936X
    Electronic ISSN: 1520-5851
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
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  • 9
    Publication Date: 2016-10-22
    Description: Carbonate concretions hosted within organic carbon-rich shale sequences represent unique archives of often exceptionally preserved fossil biota. Besides providing high-fidelity preservation, their geochemical signatures can provide insight into the physical and chemical processes during early and later-stage concretion growth. Here, two fossiliferous carbonate concretions of the late Early Cretaceous Santana Formation (Araripe Basin, north-east Brazil) are analysed with an integrative geochemical approach including μ -XRF scanning, δ 13 C, δ 18 O, 87 Sr/ 86 Sr and Δ 47 (clumped-isotope thermometry). Individual concretions show a concentric internal zonation with the outermost layer being composed of millimetre-thick cone-in-cone calcite. A strong covariance of δ 13 C and δ 18 O values of the fine-crystalline concretion body indicates mixing of two different carbonate phases and supports a scenario of temporally separated pervasive growth stages. Microbially-mediated formation of an early porous calcite framework was controlled by the combined processes of fermentation and methanogenesis around the decaying carcass, forming localized environments within a zone of sulphate reduction. Microbial sulphate reduction is indicated by the concentric enrichment of pyrite in the outer part of the concretion body and by high pyrite abundance in the surrounding shale. Information on the later-stage diagenetic processes affecting the Santana concretions can be derived from the outermost fringing cone-in-cone calcite. The carbonate precipitating fluid was characterized by a more or less marine δ 18 O composition (calculated δ 18 O porewater = -1.0 to -1.8‰) and by radiogenic Sr-isotope ratios (up to 0.713331 ± 7.0*10 -6 ), the latter probably reflecting modification due to interaction with the surrounding shale or, alternatively, with underlying evaporitic sulphate deposits influenced by strong continental inflow or with crystalline basement rocks. The Δ 47 -derived temperature estimates range between 37 to 42°C ± 5, indicating precipitation of the cone-in-cone calcite at a depth of 650 to 850 m, which is only half as much as the maximum burial depth derived from existing fission-track data. Overall, the study of fossiliferous carbonate concretions in organic carbon-rich sedimentary sequences can reveal a complex growth history spanning incipient microbially-influenced precipitates as well as later-stage burial diagenetic phases. This article is protected by copyright. All rights reserved.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 10
    Publication Date: 2017-11-16
    Description: Carbonate clumped isotopes offer a potentially transformational tool to interpret Earth's history, but the proxy is still limited by poor inter-laboratory reproducibility. Here, we focus on the uncertainties that result from the analysis of only a few replicate measurements to understand the extent to which unconstrained errors affect calibration relationships and paleoclimate reconstructions. We find that highly precise data can be routinely obtained with multiple replicate analyses, but this is not always done in many laboratories. For instance, using published estimates of external reproducibilities we find that typical clumped isotope measurements (3 replicate analyses) have margins of error at the 95% confidence level (CL) that are too large for many applications. These errors, however, can be systematically reduced with more replicate measurements. Second, using a Monte Carlo-type simulation we demonstrate that the degree of disagreement on published calibration slopes is about what we should expect considering the precision of Δ 47 data, the number of samples and replicate analyses, and the temperature range covered in published calibration. Finally, we show that the way errors are typically reported in clumped isotope data can be problematic and lead to the impression that data is more precise than warranted. We recommend that uncertainties in Δ 47 data should no longer be reported as the standard error of a few replicate measurements. Instead, uncertainties should be reported as margins of error at a specified confidence level (e.g., 68% or 95% CL). These error bars are a more realistic indication of the reliability of a measurement.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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