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  • 1
    Electronic Resource
    Electronic Resource
    Late quaternary sediments in Lake Zürich, Switzerland (1983)
    Springer
    Environmental geology 5 (1983), S. 191-205 
    Details
    ISSN: 1432-0495
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Lake Zürich occupies a glacially overdeepened perialpine trough in the northern Middlelands of Switzerland. A total of 154.4 m of Quaternary sediments and 47.3 m of Tertiary Molasse bedrock has been cored from the deepest part of the lake, some 10 km south of the city of Zürich. Some 16.8 m of gravels and sands directly overlying the bedrock include basal till and probably earliest subglacial fluvial and lacustrine deposits. These are overlain by 98.6 m of fine-grained, glacial-aged sediments comprising completely deformed proglacial and/or subglacial lacustrine muds, separated by four basal mud tills. The lack of interglacial sediments, fossils, and other datable material, and the presence of severe sediment deformation and unknown amounts of erosion prevent the establishment of an exact chronostratigraphy for sediments older than the upper mud till. Above it some 8.6 m of lacustrine muds were deposited, folded, faulted, and tilted during the final opening of the lake at about 17,500–17,000 years ago. Superimposed are 30.4 m of final Würm and post-glacial sediments comprising (from oldest): cyclic proglacial mud, thick-bedded and laminated mud, a complex transition zone, laminated carbonate, laminated marl, and diatom-calcite varves. These sediments reflect changing catchment and lacustrine conditions including: glacial proximity, catchment stability, lake inflow characteristics, thermal structure, chemistry, and bed stability. Average sedimentation rates ranged from 11 cm yr−1 immediately after glacier withdrawal, to as low as 0.4 mm yr−1 as the environment stabilized. The lack of coarse outwash deposits separating the fine-grained glaciolacustrine sediments from a corresponding underlying basal till suggests that deglaciation of the deep northern basin of Lake Zürich was by stagnation-zone retreat rather than by retreat of an active ice-front.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02414864
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  • 2
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    Architecture and facies differentiation within a Middle Miocene carbonate platform, Ermenek, Mut Basin, southern Turkey (2010)
    In:  Geological Society Special Publication 329: 265-290.
    Details
    Publication Date: 2010-04-01
    Description: In south-central Turkey, a carbonate platform system of early middle Miocene age is exposed in three-dimensional outcrops displaying a rich variety of carbonate facies associated with exceptionally well-preserved depositional geometries. This paper presents a detailed reconstruction of the geometries and facies organization across the prograding margin of one intra-platform carbonate bank that grew during the Langhian on the Ermenek Platform. The total thickness of the margin is approximately 250 m, and it has prograded over a distance of 1.2 km. The geometrical pattern shows an alternation between sigmoid, sigmoid-oblique, and oblique accretionary units at different scales. Based on the facies distribution and the geometrical framework two large-scale depositional sequences and eight medium-scale depositional sequences were defined. The general evolution from a low-angle shelf geometry to a prograding flat-topped platform was associated with an evolution from oligophotic-dominated carbonate producers, such as large benthic foraminifera, molluscs, echinoderms, red algae and bryozoans at the base, to mesophotic and euphotic carbonate producer organisms, such as corals, red algae and porcellaneous small benthic foraminifera at the top. The eight medium cycles were defined primarily using the depositional geometries, since facies changes were observed only locally within these cycles. Several mechanisms influenced the stratigraphic architecture of this margin: (1) eustatic sea-level controlled the overall transgressive-regressive Langhian sequence, and two superposed large-scale sequences. Medium cycles were probably also influenced by higher frequency sea-level fluctuations; (b) climate change probably influenced the overall evolution of the faunal assemblage; and (c) antecedent topography determined the overall architecture of a shelf bordering a deeper basin.
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  • 3
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    Canyon morphology on a modern carbonate slope of the Bahamas: Evidence of regional tectonic tilting (2012)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2012-09-01
    Description: New high-quality multibeam data presented here depict the northern slope of the Little Bahama Bank (Bahamas). The survey reveals the details of large- and small-scale morphologies that look like siliciclastic systems at a smaller scale, including large-scale slope failure scars and canyon morphologies, previously interpreted as gullies and creep lobes. The slope exhibits mature turbidite systems built by mass-flow events and turbidity currents. The sediment transport processes are probably more complex than expected. Slope failures show sinuous head scarps with various sizes, and most of the scars are filled with recent sediment. Canyons have amphitheater-shaped heads resulting from coalescing slump scars, and are floored by terraces that are interpreted as slump deposits. Canyons rapidly open on a short channel and a depositional fan-shaped lobe. The entire system extends for ~40 km. The development of these small turbidite systems, similar to siliciclastic systems, is due to the lack of cementation related to alongshore current energy forcing the transport of fine particles and flow differentiation. Detailed analyses of bathymetric data show that the canyon and failure-scar morphology and geometry vary following a west-east trend along the bank slope. The changing parameters are canyon length and width, depth of incision, and canyon and channel sinuosity. Accordingly, failure scars are larger and deeper eastward. These observations are consistent with a westward tectonic tilt of the bank during the Cenozoic.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 4
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    First Discovery of Channel-Levee Complexes In A Modern Deep-Water Carbonate Slope Environment (2014)
    Society for Sedimentary Geology (SEPM)
    Details
    Publication Date: 2014-11-22
    Description: A bstract :  New high-quality high-resolution seismic data along the western slope of the Great Bahama Bank reveals a present-day channel–levee complex developed in a pure carbonate setting. This complex grew over two buried complexes separated by erosion surfaces, suggesting both the continuity of downslope gravity-driven processes along this carbonate slope, and channel migration through avulsion, processes similar to what happens along siliciclastic slopes. Complex morphology and geometry are similar to analogs described in siliciclastic systems, but the size of the presented carbonate complex is smaller by a factor of ten. Integrating high-resolution seismic and core studies shows that this complex was built by the stacking of gravity-flow deposits, including turbidites. It presently is inactive and buried by deposits from hemipelagic fallout or low-energy density processes channeled by the gully network; Recent sediments are reworked by along-slope bottom currents dominated by internal tides. The discovery of these channel–levee complexes has implications both on the conceptual models describing the behavior of carbonate slope systems and on hydrocarbon exploration by enhancing the reservoir-bearing potential of carbonate slopes.
    Print ISSN: 1527-1404
    Topics: Geosciences
    Published by Society for Sedimentary Geology (SEPM)
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  • 5
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    Holocene Indian Ocean tsunami history in Sri Lanka (2014)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2014-09-20
    Description: Sediment cores from Karagan Lagoon in southeastern Sri Lanka retrieved deposits from the A.D. 2004 Indian Ocean tsunami and older similar deposits that provide evidence for a tsunami 2417 ± 152 cal. (calendar) yr B.P. to 2925 ± 98 cal. yr B.P., and for six tsunamis between 4064 ± 128 cal. yr B.P. and 6665 ± 110 cal. yr B.P., a period for which the sediment record appears continuous. Radiocarbon dating indicates that the recurrence interval is variable, ranging from 181–517 yr to 1045 ± 334 yr, with a mean recurrence interval of 434 ± 40 yr during the ca. 4000–7000 cal. yr B.P. continuous interval. Assuming that these tsunamis were generated by giant earthquakes along the Sumatra-Andaman subduction zone, a reasonable assumption for this far-field transoceanic location, this record extends the giant-earthquake history for the Indian Ocean region. The longest recurrence interval of more than 1000 yr implies that earthquakes along the subduction zone may reach twice the size of the 2004 earthquake.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 6
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    Periplatform drift: The combined result of contour current and off-bank transport along carbonate platforms (2014)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2014-09-20
    Description: Hydroacoustic and sedimentological data from the western leeward flank of the Great Bahama Bank document the interplay of off-bank sediment export, along-slope transport, and erosion, which together shape facies and thickness distribution of slope carbonates. The integrated data set depicts the combined product of these processes and allows formulation of a comprehensive model of a periplatform drift that significantly amends established models of carbonate platform slope facies distribution and geometry. The basinward-thinning wedge of the periplatform drift at the foot of the bank escarpment displays along-slope and downslope variations in sedimentary architecture. Sediments are muddy carbonate sands that coarsen basinward. The drift wedge has a pervasive cover of cyclic steps. In zones of lower contour current speed, depth-related facies belts develop, whereas strike-discontinuous sediment lobes, scarps, and gullies characterize areas with higher current speed. This understanding of the impact of currents on carbonate-slope sedimentation has wider implications for seismic and sequence stratigraphic interpretation of carbonate platforms and for applied aspects such as hydrocarbon exploration.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 7
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    The fertilization of the Bahamas by Saharan dust: A trigger for carbonate precipitation? (2014)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2014-07-31
    Description: The enigma of the Bahamas is that this highly productive carbonate system has existed for at least 100 m.y., building a vast edifice of carbonates, thousands of meters thick, in an essentially nutrient-poor environment. Based on measurements of the insoluble material, the Fe and Mn in the carbonate fraction, and the 15 N of the sedimentary organic matter, we suggest a paradigm shift in order to explain the formation of the Bahamas and possibly other similar platforms. We propose that the Great Bahama Bank is currently, and may in the past have been, fertilized by atmospheric dust, promoting the fixation of atmospheric N 2 by cyanobacteria. These cyanobacteria provided a source of nitrogen to the rest of the community in this nutrient-poor environment. The fixation of N has imparted a characteristic 15 N signal and has been responsible, through the drawdown of CO 2 , for initiating the precipitation of carbonate in the shallow waters. This phenomenon might be responsible for the formation of vast amounts of sediments in the oceans, not only within recent times, but throughout geological history, particularly in the early history of the Earth prior to the existence of calcium carbonate–secreting organisms.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Characteristics of porosity and permeability layer of fossil Halimeda reef mineral rock of Miocene in the Xisha Islands and its genetic model (2015)
    Springer
    Details
    Publication Date: 2015-04-01
    Print ISSN: 0253-505X
    Electronic ISSN: 1869-1099
    Topics: Geosciences , Physics
    Published by Springer
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  • 9
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    Biogenic carbonate formation and sedimentation in the Xisha Islands: evidences from living Halimeda (2015)
    Springer
    Details
    Publication Date: 2015-04-01
    Print ISSN: 0253-505X
    Electronic ISSN: 1869-1099
    Topics: Geosciences , Physics
    Published by Springer
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  • 10
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    Electrical and fluid flow properties of carbonate microporosity types from multiscale digital image analysis and mercury injection (2015)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2015-11-03
    Description: Electrical and fluid flow properties of porous media are directly related to the morphology of pores and the connectivity of the pore network. Both are closely linked to the amount and type of intrinsic microporosity in carbonate rocks, which is not resolved by conventional techniques. Broad-ion-beam (BIB) milling produces high-quality true-two-dimensional cross sections for scanning electron microscopy (SEM) and enables accurate quantification of carbonate microporosity for the first time. The combination of BIB-SEM mosaics with optical micrographs yields a multiscale digital image analysis (MsDIA) spanning six orders of magnitude. In this paper, the pore structures of 12 different carbonate rock samples from various rock types are quantified using MsDIA. Mercury injection capillary pressure measurements are used to assess pore-throat properties. The quantified pore-structure parameters are correlated with plug measurements of electrical resistivity and permeability. Results indicate that petrophysical properties are closely linked to the type of microporosity, which is distinctive for a certain rock type. Rock types with crystalline microporosity, such as mudstone and dolomite, generally show good connectivity, in which the size of the pore-network determines if the rock favors either hydraulic or electric flow. Rock types with intercement or micromoldic microporosity, such as bindstone and travertine, show variations in connectivity due to layering and moldic micropores of biological origin. Furthermore, pore-size distributions (PSD) follow a power law in all samples, despite their depositional and diagenetic differences. The slope of the PSD correlates with the electric properties, in which samples with a steeper slope show lower cementation factors. The linearity of the power law distribution enables predictions of pore populations outside the investigated length scales.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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