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  • 552.5
  • Karbonatische Sedimentgesteine
  • English  (7)
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  • 1
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    What Can We Learn From X-Ray Fluorescence Core Scanning Data? A Paleomonsoon Case Study (2021)
    Details
    Publication Date: 2021-10-07
    Description: X-ray fluorescence (XRF) core scanning of marine and lake sediments has been extensively used to study changes in past environmental and climatic processes over a range of timescales. The interpretation of XRF-derived element ratios in paleoclimatic and paleoceanographic studies primarily considers differences in the relative abundances of particular elements. Here we present new XRF core scanning data from two long sediment cores in the Andaman Sea in the northern Indian Ocean and show that sea level related processes influence terrigenous inputs based proxies such as Ti/Ca, Fe/Ca, and elemental concentrations of the transition metals (e.g., Mn). Zr/Rb ratios are mainly a function of changes in median grain size of lithogenic particles and often covary with changes in Ca concentrations that reflect changes in biogenic calcium carbonate production. This suggests that a common process (i.e., sea level) influences both records. The interpretation of lighter element data (e.g., Si and Al) based on low XRF counts is complicated as variations in mean grain size and water content result in systematic artifacts and signal intensities not related to the Al or Si content of the sediments. This highlights the need for calibration of XRF core scanning data based on discrete sample analyses and careful examination of sediment properties such as porosity/water content for reliably disentangling environmental signals from other physical properties. In the case of the Andaman Sea, reliable extraction of a monsoon signal requires accounting for the sea level influence on the XRF data.
    Keywords: 552.5 ; marine sediments ; lake sediments ; core scanning ; X‐ray fluorescence (XRF ; sediment properties
    Language: English
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  • 2
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    Rock magnetics of carbonate systems–investigating palaeodune archives on Fuerteventura (Canary Islands) (2021)
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    Publication Date: 2021-10-13
    Description: The mineral magnetic properties of Pleistocene aeolian dune sands from the island of Fuerteventura (Canary Islands, Spain) were studied in order to reconstruct the palaeoenvironmental evolution of Pleistocene climates during their formation. The palaeodunes on Fuerteventura mainly consist of carbonate sands admixed with dust and material of volcanic origin. Due to the low magnetic background caused by the diamagnetic character of carbonate sands, these archives offer a lot of potential for environmental magnetic studies to detect the imprint of dust, volcanic material and paedogenesis. Four sections of alternating palaeosurface–aeolianite sequences in palaeodune fields have been analysed by means of extensive rock magnetic measurements. These Quaternary archives consist of deposits originating from different sources. I. material blown from the shallow shelf, II. material of volcanic origin, and III. long-range transported dust. The rock magnetic findings enable a more detailed interpretation of the palaeosurfaces within the sequences. We are able to differentiate semiquantitatively between the different source materials on one hand and to distinguish on the other hand those from soil-forming processes. Soil formation is only weakly developed in the dust imprints in the palaeosol aeolianite sequences, linked to sparse vegetation cover during the Pleistocene on Fuerteventura.
    Keywords: 552.5 ; 538.727 ; aeolianite ; environmental magnetics ; palaeosol ; Pleistocene ; Quaternary
    Language: English
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  • 3
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    Permeability Variations in Illite-Bearing Sandstone: Effects of Temperature and NaCl Fluid Salinity (2021)
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    Publication Date: 2021-09-06
    Description: Temperature changes and variations in pore fluid salinity may negatively affect the permeability of clay-bearing sandstones with implications for natural fluid flow and geotechnical applications alike. In this study these factors are investigated for a sandstone dominated by illite as the clay phase. Systematic long-term flow-through experiments were conducted and complemented with comprehensive microstructural investigations and the application of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to explain mechanistically the observed permeability changes. Initially, sample permeability was not affected by low pore fluid salinity indicating strong attraction of the illite particles to the pore walls as supported by electron microprobe analysis (EMPA). Increasing temperature up to 145°C resulted in an irreversible permeability decrease by 1.5 orders of magnitude regardless of the pore fluid composition (i.e., deionized water and 2 M NaCl solution). Subsequently diluting the high salinity pore fluid to below 0.5 M yielded an additional permeability decline by 1.5 orders of magnitude, both at 145°C and after cooling to room temperature. By applying scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) thermo-mechanical pore throat closure and illite particle migration were identified as independently operating mechanisms responsible for observed permeability changes during heating and dilution, respectively. These observations indicate that permeability of illite-bearing sandstones will be impaired by heating and exposure to low salinity pore fluids. In addition, chemically induced permeability variations proved to be path dependent with respect to the applied succession of fluid salinity changes.
    Keywords: 552.5 ; permeability ; illite ; sandstone ; flow-through experiments ; microstructure ; DLVO theory
    Language: English
    Type: article
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  • 4
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    Diagnostic criteria using microfacies for calcareous contourites, turbidites and pelagites in the Eocene–Miocene slope succession, southern Cyprus (2021)
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    Publication Date: 2021-09-06
    Description: Interbedded contourites, turbidites and pelagites are commonplace in many deep-water slope environments. However, the distinction between these different facies remains a source of controversy. This detailed study of calcareous contourites and associated deep-marine facies from an Eocene–Miocene sedimentary succession on Cyprus clearly documents the diagnostic value of microfacies in this debate. In particular, the variability of archetypical bi-gradational contourite sequences and their internal subdivision (bedding, layering and lamination) are explored. Contourites can be distinguished from turbidites, pelagites and hemipelagites by means of carbonate microfacies in combination with bed-scale characteristics. Particle composition provides valuable information on sediment provenance. Depositional texture, determined by the ratio between carbonate mud and bioclasts, is crucial for identifying bi-gradational sequences in both muddy and sandy contourites, and normally-graded sequences in turbidite beds. Equally important are the type and preservation of traction structures, as well as the temporality and impact of bioturbation. Shell fragmentation under conditions of increased hydrodynamic agitation (textural inversion) is recognized as a carbonate-specific feature of bioclastic sandy contourites.
    Keywords: 552.5 ; Carbonate microfacies ; continental slope ; contourites ; Cyprus ; deep-marine deposits ; pelagites ; turbidites
    Language: English
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  • 5
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    Palaeoenvironmental evolution of the Tunisian carbonate platform margin (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: The Late BarremianLate Aptian interval was characterised by several major changes in the ocean/climate system related to the onset of the Mid-Cretaceous greenhouse world. North Africansedimentary deposits offer excellent archives of the ecological changes on the southern Tethyscontinental margin during this time interval. In the present phD thesis sedimentology, palaeontology,biostratigraphy, chemostratigraphy, and geochemistry are combined to reconstruct the palaeoenvironmental evolution and sea-level changes of the Tunisian carbonate platform margin.Respect is paid to major palaeoceanographic and palaeoclimatic events including the late Early Aptian Oceanic Anoxic Event 1a (OAE 1a) and two time intervals associated with widespread carbonate platform drowning in the early- and mid-Late Aptian. The last chapter deals with the cephalopod fauna of the platform margin. Results of the detailed regional investigations are compared to global marine palaeoenvironments and discussed in a broad geological context...
    Description: thesis
    Keywords: 551.77 ; 551 ; 550 ; TWC 600 ; VKB 372 ; VEN 130 ; VDH 300 ; Paläoklimatologie ; Karbonatische Sedimentgesteine ; Tunesien {Geologie} ; Kreide
    Language: English
    Type: monograph , publishedVersion
    Format: 160 S.
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  • 6
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    Pedogenic carbonates as a proxy for palaeo-CO2 in the Palaeozoic atmosphere (2010)
    Elsevier
    Details
    Publication Date: 2021-03-29
    Description: According to a model by Cerling (1991, 1999), the carbon isotope composition of calcretes should depend on the soil type and the CO2-concentration in the atmosphere. We have tested Cerling’s model by investigating 14 Palaeozoic sections with soil profiles. A large number of carbonate types of different genetic origin exist in the localities examined. Comparing the Palaeozoic samples with recent and subrecent calcretes, it can be demonstrated that anhedral, cryptocrystalline (〈10 μm) and subhedral microcrystalline (10 - 40 μm) carbonates are clearly of pedogenic origin. Crystals of larger size with a poikilotopic texture are of groundwater or burial diagenetic origin. Macro- and micromorphological features, typical of recent calcretes, occur in several soil profiles, but thin section microscopy reveals a strong diagenetic overprint of most pedogenic carbonates. Time equivalent sections with comparable soil types (protosols, calcisols and vertisols) show large variations in carbon isotope composition. On the other hand, different carbonate generations at one site do not differ much. Therefore Palaeozoic calcretes appear to be unsuitable for a deduction of the Palaeozoic CO2-concentration.
    Description: German Research Foundation (DFG)
    Description: research
    Keywords: 551.9 ; 552.5 ; VKB 350 ; VJJ 110 ; VCA 300 ; VKB 332 ; VKA 300 ; VKB 371 ; VEA 000 ; VKB 372 ; Lithogenese {Sedimentologie} ; Geochemie der Stabilen Isotopen ; Paläozoische Geologie ; Sedimentationsbedingungen ; Petrogenese ; Klastische Sedimentgesteine ; Europa insgesamt {Geologie} ; Karbonatische Sedimentgesteine ; Kohlenstoffkreislauf ; C-isotope ; Jungpaläozoikum ; Paläopedologie ; Kalkkruste ; CO2 ; calcrete ; carbon cycle ; upper Paleozoic ; paleosol ; C-13/C-12 ; Europa ; paläoklima ; Europe ; 38.41 ; 38.61 ; 38.32
    Language: English
    Type: article
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  • 7
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    Diagenetic imprints on magnetic mineral assemblages in marine sediments (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Diagenesis, Rock magnetism, Marine sediments. - Sediments and sedimentary rocks are important sources for paleomagnetic studies of the geomagnetic field behaviour and of environmental changes. These studies are greatly dependent on the reliable extraction of the detrital magnetic signal. Overprinting of this signal by reductive diagenetic processes, where iron-bearing minerals are dissolved and secondary (magnetic) sulphide minerals form, jeopardizes the validity of such investigations. It is therefore necessary to be aware of the possible presence of diagenetic/authigenic magnetic phases, i.e. greigite, and their influence on the paleomagnetic signal. A chemical remanent magnetisation (CRM) due to these phases can obscure the detrital magnetic signal. It remains to be shown how primary detrital minerals may survive dissolution under these conditions, and by which mechanisms secondary (magnetic) sulphide minerals are formed.
    Description: thesis
    Keywords: 538.7 ; 552.5 ; 550 ; TOT 310 ; VKB 323 ; TOT 310 ; VKB 323 ; Gesteinsmagnetismus {Geophysik} ; Sedimentphysik
    Language: English
    Type: monograph , publishedVersion
    Format: 118 S.
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