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Type: article × Publisher: Amsterdam [u.a.] : Elsevier × WGL Institute: LIAG ×

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Now showing 1 - 5 of 5
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    Visualisation and analysis of shear-deformation bands in unconsolidated Pleistocene sand using ground-penetrating radar: Implications for paleoseismological studies
    (Amsterdam [u.a.] : Elsevier, 2018) Brandes, Christian; Igel, Jan; Loewer, Markus; Tanner, David C.; Lang, Jörg; Müller, Katharina; Winsemann, Jutta
    Deformation bands in unconsolidated sediments are of great value for paleoseismological studies in sedimentary archives. Using ground-penetrating radar (GPR), we investigated an array of shear-deformation bands that developed in unconsolidated Pleistocene glacifluvial Gilbert-type delta sediments. A dense grid (spacing 0.6 m) of GPR profiles was measured on top of a 20 m-long outcrop that exposes shear-deformation bands. Features in the radargrams could be directly tied to the exposure. The shear-deformation bands are partly represented by inclined reflectors and partly by the offset of reflections at delta clinoforms. 3-D interpretation of the 2-D radar sections shows that the bands have near-planar geometries that can be traced throughout the entire sediment volume. Thin sections of sediment samples show that the analysed shear-deformation bands have a denser grain packing than the host sediment. Thus they have a lower porosity and smaller pore sizes and therefore, in the vadose zone, the deformation bands have a higher water content due to enhanced capillary forces. This, together with the partially-developed weak calcite cementation and the distinct offset along the bands, are likely the main reasons for the clear and unambiguous expression of the shear-deformation bands in the radar survey. The study shows that deformation-band arrays can clearly be detected using GPR and quickly mapped over larger sediment volumes. With the 3-D analysis, it is further possible to derive the orientation and geometry of the bands. This allows correlation of the bands with the regional fault trend. Studying deformation bands in unconsolidated sediments with GPR is therefore a powerful approach in paleoseismological studies. Based on our data, we postulate that the outcrop is part of a dextral strike-slip zone that was reactivated by glacial isostatic adjustment.
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    Seismic interpretation and structural restoration of the Heligoland glaciotectonic thrust-fault complex: Implications for multiple deformation during (pre-)Elsterian to Warthian ice advances into the southern North Sea Basin
    (Amsterdam [u.a.] : Elsevier, 2020) Winsemann, Jutta; Koopmann, Hannes; Tanner, David C.; Lutz, Rüdiger; Lang, Jörg; Brandes, Christian; Gaedicke, Christoph
    Despite a long history of research, the locations of former ice-margins in the North Sea Basin are still uncertain. In this study, we present new palaeogeographic reconstructions of (pre-) Elsterian and Warthian ice-margins in the southeastern North Sea Basin, which were previously unknown. The reconstructions are based on the integration of palaeo-ice flow data derived from glaciotectonic thrusts, tunnel valleys and mega-scale glacial lineations. We focus on a huge glaciotectonic thrust complex located about 10 km north of Heligoland and 50 km west of the North Frisian coast of Schleswig-Holstein (Northern Germany). Multi-channel high-resolution 2D seismic reflection data show a thrust-fault complex in the upper 300 ms TWT (ca. 240 m) of seismic data. This thrust-fault complex consists of mainly Neogene delta sediments, covers an area of 350 km2, and forms part of a large belt of glaciotectonic complexes that stretches from offshore Denmark via northern Germany to Poland. The deformation front of the Heligoland glaciotectonic complex trends approximately NNE-SSW. The total length of the glaciotectonic thrust complex is approximately 15 km. The thrust faults share a common detachment surface, located at a depth of 250–300 ms (TWT) (200–240 m) below sea level. The detachment surface most probably formed at a pronounced rheological boundary between Upper Miocene fine-grained pro-delta deposits and coarser-grained delta-front deposits, although we cannot rule out that deep permafrost in the glacier foreland played a role for the location of this detachment surface. Restored cross-sections reveal the shortening of the complex along the detachment to have been on average 23% (ranging from ca. 16%–50%). The determined ice movement direction from east-southeast to southeast suggests deformation by an ice advance from the Baltic region. The chronospatial relationship of the thrust-fault complex and adjacent northwest-southeast to northeast-southwest trending Elsterian tunnel valleys implies a pre-Elsterian (MIS 16?) age of the glaciotectonic complex. However, the age of these Elsterian tunnel valleys is poorly constrained and the glaciotectonic complex of Heligoland may also have been formed during an early Elsterian ice advance into the southeastern North Sea Basin. The glaciotectonic complex underwent further shortening and the Elsterian tunnel-valley fills that were incised into the glaciotectonic complex were partly deformed during the Saalian Drenthe and Warthe (1) ice advances.
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    Measuring and evaluating colorimetric properties of samples from loess-paleosol sequences
    (Amsterdam [u.a.] : Elsevier, 2023) Laag, Christian; Lagroix, France; Kreutzer, Sebastian; Chapkanski, Stoil; Zeeden, Christian; Guyodo, Yohan
    Colorimetric measurements are valuable in studying paleoenvironmental changes in sediment archives such as loess-paleosol sequences. These measurements allow for the identification of climate-sensitive minerals such as hematite, goethite, and secondary carbonates, as well as the observation of stratigraphic changes influenced by paleoclimate variations. Herein, a detailed workflow protocol emphasizing mineral abundance extraction by determining true band amplitudes is presented. Moreover, we present a protocol for colorimetric measurements that eliminates container bias, allowing the analysis and re-analysis of stored sediment quickly and inexpensively. Finally, we introduce a new R-package ('LESLIE') for graphical data display and enhancement. The protocol and its validation are demonstrated on the Suhia Kladenetz loess-paleosol sequence of northern Bulgaria. • A detailed workflow protocol eliminating container bias in colorimetric measurements and extracting mineral abundances is presented. • The protocol is independently validated with aid of Attenuated Total Reflectance Fourier Transform mid-infrared (ATR-FTIR) spectroscopic experiments. • Stratigraphic color enhancement using the R-package 'LESLIE' is facilitated by a user-friendly R-shiny application.
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    New investigations at Kalambo Falls, Zambia: Luminescence chronology, site formation, and archaeological significance
    (Amsterdam [u.a.] : Elsevier, 2015) Duller, Geoff A. T.; Tooth, Stephen; Barham, Lawrence; Tsukamoto, Sumiko
    Fluvial deposits can provide excellent archives of early hominin activity but may be complex to interpret, especially without extensive geochronology. The Stone Age site of Kalambo Falls, northern Zambia, has yielded a rich artefact record from dominantly fluvial deposits, but its significance has been restricted by uncertainties over site formation processes and a limited chronology. Our new investigations in the centre of the Kalambo Basin have used luminescence to provide a chronology and have provided key insights into the geomorphological and sedimentological processes involved in site formation. Excavations reveal a complex assemblage of channel and floodplain deposits. Single grain quartz optically stimulated luminescence (OSL) measurements provide the most accurate age estimates for the youngest sediments, but in older deposits the OSL signal from some grains is saturated. A different luminescence signal from quartz, thermally transferred OSL (TT-OSL), can date these older deposits. OSL and TT-OSL results are combined to provide a chronology for the site. Ages indicate four phases of punctuated deposition by the dominantly laterally migrating and vertically aggrading Kalambo River (∼500-300 ka, ∼300-50 ka, ∼50-30 ka, ∼1.5-0.49 ka), followed by deep incision and renewed lateral migration at a lower topographic level. A conceptual model for site formation provides the basis for improved interpretation of the generation, preservation, and visibility of the Kalambo archaeological record. This model highlights the important role of intrinsic meander dynamics in site formation and does not necessarily require complex interpretations that invoke periodic blocking of the Kalambo River, as has previously been suggested. The oldest luminescence ages place the Mode 2/3 transition between ∼500 and 300 ka, consistent with other African and Asian sites where a similar transition can be found. The study approach adopted here can potentially be applied to other fluvial Stone Age sites throughout Africa and beyond.
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    3D architecture of cyclic-step and antidune deposits in glacigenic subaqueous fan and delta settings: Integrating outcrop and ground-penetrating radar data
    (Amsterdam [u.a.] : Elsevier, 2017) Lang, Jörg; Sievers, Julian; Loewer, Markus; Igel, Jan; Winsemann, Jutta
    Bedforms related to supercritical flows are increasingly recognised as important constituents of many depositional environments, but outcrop studies are commonly hampered by long bedform wavelengths and complex three-dimensional geometries. We combined outcrop-based facies analysis with ground-penetrating radar (GPR) surveys to analyse the 3D facies architecture of subaqueous ice-contact fan and glacifluvial delta deposits. The studied sedimentary systems were deposited at the margins of the Middle Pleistocene Scandinavian ice sheets in Northern Germany. Glacifluvial Gilbert-type deltas are characterised by steeply dipping foreset beds, comprising cyclic-step deposits, which alternate with antidune deposits. Deposits of cyclic steps consist of lenticular scours infilled by backset cross-stratified pebbly sand and gravel. The GPR sections show that the scour fills form trains along the delta foresets, which can locally be traced for up to 15 m. Perpendicular and oblique to palaeoflow direction, these deposits appear as troughs with concentric or low-angle cross-stratified infills. Downflow transitions from scour fills into sheet-like low-angle cross-stratified or sinusoidally stratified pebbly sand, deposited by antidunes, are common. Cyclic steps and antidunes were deposited by sustained and surge-type supercritical density flows, which were related to hyperpycnal flows, triggered by major meltwater discharge or slope-failure events. Subaqueous ice-contact fan deposits include deposits of progradational scour fills, isolated hydraulic jumps, antidunes and (humpback) dunes. The gravel-rich fan succession consists of vertical stacks of laterally amalgamated pseudo-sheets, indicating deposition by pulses of waning supercritical flows under high aggradation rates. The GPR sections reveal the large-scale architecture of the sand-rich fan succession, which is characterised by lobe elements with basal erosional surfaces associated with scours filled with backsets related to hydraulic jumps, passing upwards and downflow into deposits of antidunes and (humpback) dunes. The recurrent facies architecture of the lobe elements and their prograding and retrograding stacking pattern are interpreted as related to autogenic flow morphodynamics.