The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Lars Nielsen - One of the best experts on this subject based on the ideXlab platform.
-
sea level proxies in holocene Raised Beach ridge deposits greenland revealed by ground penetrating radar
Scientific Reports, 2017Co-Authors: Lars Nielsen, Mikkel U Hede, Lars B Clemmensen, Aart Kroon, Mette Bendixen, Ronny Weβling, Bo ElberlingAbstract:Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic Beach ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the Beach ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of Beachface deposits and upper shoreface deposits; the contact between steeply dipping Beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied Beach ridge systems represent long time intervals and only relatively small spatial extents.
-
changes in holocene relative sea level and coastal morphology a study of a Raised Beach ridge system on samso southwest scandinavia
The Holocene, 2015Co-Authors: Mikkel U Hede, Lasse Sander, Lars B Clemmensen, Aart Kroon, Morten Pejrup, Lars NielsenAbstract:Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a Raised Beach ridge system on the island of Samso, Denmark. The internal architecture of the Beach ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the Beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that Beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the Beach steps should be corrected for Beach step height in order to be used as a marker of sea-level. Identification of Beach steps in combination with observed changes in dips of the interpreted Beachface reflections can give information about changes in the morphodynamic conditions of Beach ridge progradation through time. The vertical levels of identified downlap points are combined with an age m...
-
internal architecture of a Raised Beach ridge system anholt denmark resolved by ground penetrating radar investigations
Sedimentary Geology, 2010Co-Authors: Lars B Clemmensen, Lars NielsenAbstract:Abstract The internal architecture of Raised Beach ridge and associated swale deposits on Anholt records an ancient sea level. The Holocene Beach ridges form part of a progradational Beach ridge plain, which has been interpreted to have formed during an isostatic uplift and a relative fall in the sea level over the past 7700 years. The ridges are covered by pebbles and cobbles and commonly show evidence of deflation. Material presumably removed from the Beach ridges and adjacent swales form the present dune forms on Anholt. Ground-penetrating radar (GPR) reflection lines have been collected with 250 MHz shielded antennae across the fossil ridge and swale structures. The signals penetrate the subsurface to a maximum depth of ∼ 10 m below the fossil features. The GPR data resolve the internal architecture of the Beach ridges and swales with a vertical resolution of about 0.1 m. GPR mapping indicates that the Holocene Beach ridges are composed of seaward-dipping Beachface deposits as well as minor amounts of inland dipping deposits of wash-over origin. The Beachface deposits downlap on underlying shoreface deposits, and we use these surfaces as markers of a relative palaeo-sea level. The new data indicate that the highest relative sea level at about 8.5 m was reached 6500 years ago; 700 years later the relative sea level had dropped 0.7 m indicating a change in the relative sea level around 1 mm/year. This fall in the relative sea level most likely records the influence of an isostatic rebound causing younger Beach ridge deposits to indicate lower sea levels.
Lars B Clemmensen - One of the best experts on this subject based on the ideXlab platform.
-
sea level proxies in holocene Raised Beach ridge deposits greenland revealed by ground penetrating radar
Scientific Reports, 2017Co-Authors: Lars Nielsen, Mikkel U Hede, Lars B Clemmensen, Aart Kroon, Mette Bendixen, Ronny Weβling, Bo ElberlingAbstract:Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic Beach ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the Beach ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of Beachface deposits and upper shoreface deposits; the contact between steeply dipping Beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied Beach ridge systems represent long time intervals and only relatively small spatial extents.
-
changes in holocene relative sea level and coastal morphology a study of a Raised Beach ridge system on samso southwest scandinavia
The Holocene, 2015Co-Authors: Mikkel U Hede, Lasse Sander, Lars B Clemmensen, Aart Kroon, Morten Pejrup, Lars NielsenAbstract:Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a Raised Beach ridge system on the island of Samso, Denmark. The internal architecture of the Beach ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the Beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that Beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the Beach steps should be corrected for Beach step height in order to be used as a marker of sea-level. Identification of Beach steps in combination with observed changes in dips of the interpreted Beachface reflections can give information about changes in the morphodynamic conditions of Beach ridge progradation through time. The vertical levels of identified downlap points are combined with an age m...
-
internal architecture of a Raised Beach ridge system anholt denmark resolved by ground penetrating radar investigations
Sedimentary Geology, 2010Co-Authors: Lars B Clemmensen, Lars NielsenAbstract:Abstract The internal architecture of Raised Beach ridge and associated swale deposits on Anholt records an ancient sea level. The Holocene Beach ridges form part of a progradational Beach ridge plain, which has been interpreted to have formed during an isostatic uplift and a relative fall in the sea level over the past 7700 years. The ridges are covered by pebbles and cobbles and commonly show evidence of deflation. Material presumably removed from the Beach ridges and adjacent swales form the present dune forms on Anholt. Ground-penetrating radar (GPR) reflection lines have been collected with 250 MHz shielded antennae across the fossil ridge and swale structures. The signals penetrate the subsurface to a maximum depth of ∼ 10 m below the fossil features. The GPR data resolve the internal architecture of the Beach ridges and swales with a vertical resolution of about 0.1 m. GPR mapping indicates that the Holocene Beach ridges are composed of seaward-dipping Beachface deposits as well as minor amounts of inland dipping deposits of wash-over origin. The Beachface deposits downlap on underlying shoreface deposits, and we use these surfaces as markers of a relative palaeo-sea level. The new data indicate that the highest relative sea level at about 8.5 m was reached 6500 years ago; 700 years later the relative sea level had dropped 0.7 m indicating a change in the relative sea level around 1 mm/year. This fall in the relative sea level most likely records the influence of an isostatic rebound causing younger Beach ridge deposits to indicate lower sea levels.
Bo Elberling - One of the best experts on this subject based on the ideXlab platform.
-
sea level proxies in holocene Raised Beach ridge deposits greenland revealed by ground penetrating radar
Scientific Reports, 2017Co-Authors: Lars Nielsen, Mikkel U Hede, Lars B Clemmensen, Aart Kroon, Mette Bendixen, Ronny Weβling, Bo ElberlingAbstract:Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic Beach ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the Beach ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of Beachface deposits and upper shoreface deposits; the contact between steeply dipping Beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied Beach ridge systems represent long time intervals and only relatively small spatial extents.
D. H. Keen - One of the best experts on this subject based on the ideXlab platform.
-
middle pleistocene Raised Beach anomalies in the english channel regional and global stratigraphic implications
Journal of Geodynamics, 2000Co-Authors: B Van Vlietlanoe, M Laurent, J L Bahain, S Balescu, Christophe Falgueres, Michael H Field, Bernard Hallegouet, D. H. KeenAbstract:Abstract Palaeo-shore positions help to evidence long-term eustatic changes and assist in the understanding of tectonic movements at a regional scale. Raised Beaches anomalies exist in the Channel region and may result from deformations induced by neotectonic or by glacio-isostasy. The aim of this paper is to re-analyse, within their geodynamic context in the Channel and Dover Strait regions, the stratigraphy and the datings of palaeo-shores of Middle and Upper Pleistocene ages. This sector of Europe is characterised by strong geological contrasts and is controlled by two main geological boundaries: in the north, the Variscan Overthrust (corresponding approximately to the position of the Dover Strait) and, in the south, the Northern Branch of the Southern Brittany shearing zone. These two boundaries border a domain which seems to behave rather homogeneously on a large scale under the control of plate tectonics. Today, shorelines are subsiding north and south of this ‘Channel’ region. Episodic uplift largely controlled the open or closed status of the Dover Strait, especially after the Messinian and Early Quaternary, by reactivating Variscan structures. After 400 ka, global cooling allowed supplementary deformations in the area to be induced by glacio-isostatic rebound and clustered seismic activity during the phase of ice sheet building. Evidence of eight different transgressions dated by ESR from Oxygen Isotopic Stage (OIS) 13 to the end of OIS 5 shows the complexity of the sea-level records in a region unstable for isostatic and neotectonic reasons. Due to glacio-isostatic depression, transgressions are possible in late glacial times as well as during full interglacials. Most platforms were initially cut, during the Late Miocene, and seem to have been re-trimmed several times, especially by shore ice rafting since OIS 9. Regionally, the sea apparently rose to about the same level in O.I. Stages 11, 9 and 7. Glacio-isostatic and glacio-eustatic relative displacements of the sea level together with background tectonic movements have modified coastal positions and have temporarily altered the intensity of tidal currents. The oldest shoreline deposits are preserved only in subsiding areas, controlled by the deep crustal pattern. Neotectonics related to Variscan structure reactivation still dominates glacio-isostatic deformation and basin subsidence. The OIS 7 positive anomaly seems related to a regional relaxation event.
James Rose - One of the best experts on this subject based on the ideXlab platform.
-
testing the effect of bleaching on the bivalve glycymeris a case study of amino acid geochronology on key mediterranean Raised Beach deposits
Quaternary Geochronology, 2015Co-Authors: Beatrice Demarchi, Kirsty Penkman, Emily Clements, Mauro Coltorti, Renee Van De Locht, Roland Kroger, James RoseAbstract:This work focuses on the bivalve Glycymeris, commonly used in classic amino acid racemisation (AAR) studies in the Mediterranean, as part of an extensive assessment of the suitability of intra-crystalline protein diagenesis (IcPD) dating. We test the closed system behaviour (a prerequisite for IcPD studies) of Glycymeris through bleaching and heating studies, as well as fossil material sourced from Last Interglacial deposits in Sardinia (Calamosca), Mallorca (Palma Bay) and Tunisia (Hergla). Although bleaching appears to be effective in isolating an intra-crystalline fraction of proteins, this fraction may not behave as a closed system in all molluscan taxa, as we verify here for some of the fossil Glycymeris.We show that open-system behaviour can be identified by analysing the co-variance between FAA and THAA fractions and the relative THAA composition and we also provide further evidence that, for taphonomic reasons, dating the molluscan fauna does not necessarily yield age information for the sedimentary units when these contain derived shells.
