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  • 1
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    PANGAEA
    In:  Supplement to: Croizé, Delphine; Ehrenberg, Stephen N; Bjørlykke, Knut; Renard, François; Jahren, Jens (2010): Petrophysical properties of bioclastic platform carbonates: implications for porosity controls during burial. Marine and Petroleum Geology, 27(8), 1765-1774, https://doi.org/10.1016/j.marpetgeo.2009.11.008
    Publication Date: 2024-01-09
    Description: This study is based on rock mechanical tests of samples from platform carbonate strata to document their petrophysical properties and determine their potential for porosity loss by mechanical compaction. Sixteen core-plug samples, including eleven limestones and five dolostones, from Miocene carbonate platforms on the Marion Plateau, offshore northeast Australia, were tested at vertical effective stress, sigma1', of 0-70 MPa, as lateral strain was kept equal to zero. The samples were deposited as bioclastic facies in platform-top settings having paleo-water depths of 〈10-90 m. They were variably cemented with low-Mg calcite and five of the samples were dolomitized before burial to present depths of 39-635 m below sea floor with porosities of 8-46%. Ten samples tested under dry conditions had up to 0.22% strain at sigma1' = 50 MPa, whereas six samples tested saturated with brine, under drained conditions, had up to 0.33% strain. The yield strength was reached in five of the plugs. The measured strains show an overall positive correlation with porosity. Vp ranges from 3640 to 5660 m/s and Vs from 1840 to 3530 m/s. Poisson coefficient is 0.20-0.33 and Young's modulus at 30 MPa ranged between 5 and 40 GPa. Water saturated samples had lower shear moduli and slightly higher P- to S-wave velocity ratios. Creep at constant stress was observed only in samples affected by pore collapse, indicating propagation of microcracks. Although deposited as loose carbonate sand and mud, the studied carbonates acquired reef-like petrophysical properties by early calcite and dolomite cementation. The small strains observed experimentally at 50 MPa indicate that little mechanical compaction would occur at deeper burial. However, as these rocks are unlikely to preserve their present high porosities to 4-5 km depth, further porosity loss would proceed mainly by chemical compaction and cementation.
    Keywords: -; 194-1193; 194-1196; Bulk modulus; Calculated; Comment; COMPCORE; Composite Core; Coral Sea; Density, grain; DEPTH, sediment/rock; Event label; Height; Joides Resolution; Leg194; Lithology/composition/facies; Number; Ocean Drilling Program; ODP; Permeability, gas; Poisson's ratio; Porosity; Pressure, stress; Shear modulus; Texture; Velocity, compressional wave; Velocity, shear wave; Young's modulus
    Type: Dataset
    Format: text/tab-separated-values, 279 data points
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  • 2
    Publication Date: 2021-03-29
    Description: Stylolite sind raue Lösungssäume, die sich in einer großen Zahl von natürlichen Gesteinen bilden. Sie werden häufig verwendet um die Kompaktion von sedimentären Becken abzuschätzen und die Hauptspannungsrichtung zu finden. Allerdings sind die meisten Beschreibungen von Styloliten qualitativ und wir wissen nicht viel über ihre dynamische Entwicklung und den Einfluss der Spannung auf die Entwicklung der Rauhigkeit. Wir präsentieren numerische Simulationen mit deren Hilfe wir die dynamische Entwicklung von Styloliten untersuchen und erforschen, welchen Einfluss Heterogenitäten, Oberflächenenergien und Spannungen auf die Entwicklung der Rauhigkeit haben...
    Description: conference
    Keywords: 551 ; VAE 150 ; VKB 322 ; VAE 130 ; Strukturelle Erscheinungen {Strukturgeologie} ; Sedimentgefüge ; Geomechanik ; Stylolith
    Language: German
    Type: anthologyArticle , publishedVersion
    Format: application/pdf
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  • 3
    Publication Date: 2019-09-01
    Description: The efficiency of water transport to reactive peridotite is commonly the limiting factor for serpentinization of the lithospheric mantle to happen. This hydration process is typical of the oceanic lithosphere due to its thin crust and active fracturation, continuously creating new pathways for seawater, at ridge axis and subduction zones. Consequently, the extent of serpentinization is closely coupled with the intensity of the tectonic activity. Our study focuses on two sections of the South West Indian oceanic ridge, an ultra-slow spreading ridge. The very low melt production along this ridge type leads to extreme extensional regimes dominated by either magmatic or tectonic processes; this makes ultra-slow spreading ridges an ideal system to study the impact of magmatic vs tectonic extension on serpentinization along ridge axis. Three extensional regimes have been identified: volcanic, where the melt focuses leading to an up to 8 km thick basaltic crust, magmatic, characterized by a thin basaltic crust and deep seismic activity (down to 30 km depth), and amagmatic, characterized by peridotite covering the seafloor and even deeper seismic activity (down to 35 km depth). Aseismic zones are present at the surface of the magmatic and amagmatic regimes, likely associated with extensive serpentinization and efficient water supply. Based on seismic activity, we estimate that brittle damage can maintain high permeability in the case of the amagmatic and magmatic regimes while it is limited in the case of the volcanic regime. Our results indicate that oceanic ridges with spreading rates slower than 20 millimetres per year store at least 0.10 km3 of water per year in the oceanic mantle due to serpentinization. We compare these results with observations from serpentinized samples obtained during the 2018 Oman Drilling Project Phase 2. Samples have been drilled down to 400 m deep in the Oman Samail ophiolite and are composed of partially to completely serpentinized lithospheric dunite and harzburgite crosscut by multiple generations of magmatic dykes and serpentine veins. While the story of these rocks is complex, it is still possible to identify early features associated with on axis events. In agreement with our assumption that serpentinization is controlled by seismic damage, early fractures are commonly associated with enhanced serpentinization. We observe the dykes as being supplementary pathways for fluids.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 4
    Publication Date: 2007-10-08
    Description: Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 {degrees}C for six weeks using ceramic indenters under stresses in the 50-200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0-100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calcite-saturated aqueous solution show moderate indentation rate and the dry control experiments did not show any measurable deformation. The rate of calcite indentation is found to be inversely proportional to the indenter diameter, thus indicating that the process is diffusion-controlled. The microcracks in the dissolution region under the indenter dramatically enhance the rate of calcite indentation by a significant reduction of the distance of solute transport in the trapped fluid phase. This result indicates that care should be taken in extrapolating the kinetic data of pressure solution creep from one mineral to another.
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  • 5
    Publication Date: 2007-10-08
    Description: Statistical properties of crack-seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks. Crack-seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid. They represent a time-sequence record of an aseismic and anelastic process of rock deformation. The statistical characteristics of several crack-seal patterns containing several hundreds of successive cracks have been studied. Samples were collected in three different areas, gold-bearing quartz veins from Abitibi in Canada, serpentine veins from the San Andreas system in California and calcite veins from the Apennine Mountains in Italy. Digitized pictures acquired from thin sections allow accurate measurement of crack-seal growth increments. All the samples show the same statistical behaviour regardless of their geological origin. The crack-seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation. They differ from other fracture patterns, such as earthquake data, which exhibit power-law correlations (Gutenberg-Richter relationship). Crack-seal series represent a natural fossil record of stress release variations (less than 50 bars) in the crust that show a characteristic length scale, associated with the resistance of rock to effective tension, and no correlation in time.
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  • 6
    Publication Date: 2003-07-14
    Print ISSN: 1063-651X
    Electronic ISSN: 1095-3787
    Topics: Physics
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  • 7
    Publication Date: 2002-11-20
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 8
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  • 10
    Publication Date: 2019-08-01
    Description: Understanding the approach to faulting in continental rocks is critical for identifying processes leading to fracturing in geomaterials and the preparation process of large earthquakes. In situ dynamic X-ray imaging and digital volume correlation analysis of a crystalline rock core, under a constant confining pressure of 25 MPa, are used to elucidate the initiation, growth, and coalescence of microfractures leading to macroscopic failure as the axial compressive stress is increased. Following an initial elastic deformation, microfractures develop in the solid, and with increasing differential stress, the damage pervades the rock volume. The creation of new microfractures is accompanied by propagation, opening, and closing of existing microfractures, leading to the emergence of damage indices that increase as powers of the differential stress when approaching failure. A strong spatial correlation is observed between microscale zones with large positive and negative volumetric strains, microscale zones with shears of opposite senses, and microscale zones with high volumetric and shear strains. These correlations are attributed to microfracture interactions mediated by the heterogeneous stress field. The rock fails macroscopically as the microfractures coalesce and form a geometrically complex 3D volume that spans the rock sample. At the onset of failure, more than 70% of the damage volume is connected in a large fracture cluster that evolves into a fault zone. In the context of crustal faulting dynamics, these results suggest that evolving rock damage around existing locked or future main faults influences the localization process that culminates in large brittle rupture events.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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