Flooding of the southern part of the North Sea occurred between 9000 and 8000 BP, when the rate of relative sea-level rise was on the order of 0.7 cm per year for the Dover Strait Region and 1.6 cm per year for the area north of the Frisian Islands, forcing the shoreline to recede rapidly. When relative sea-level rise decelerated after 7000 BP for the Belgian coast and 6000 BP for the central Netherlands coast, sediment supply by the tidal currents balanced the creation of accommodation space in the estuaries and other back-barrier basins. Consequently, the barrier started to stabilize, and the tidal basins and their inlets silted up. Between 5500 and 4500 BP, the Belgian coastal plain changed into a freshwater marsh with peat accumulation, and the same happened 500-1000 years later in the western provinces of the Netherlands. The E-W running barrier/back-barrier system of the Frisian Islands in the northern Netherlands stayed open until today, however, because of lower sediment supply.The period between 4000 and 2000 BP was relatively quiet due to the strong deceleration of the rate of sea-level rise; peat cushions developed behind the barriers, which were straightened by erosion of the headlands. Major and often catastrophic flooding occurred in the Middle Ages, when the estuaries in the southwestern part of the Netherlands formed.About 226 (± 15%) x 10 9 m 3 sediment, mostly sand, is stored in the barriers and back-barrier basins of the Netherlands, 70% of which was deposited prior to 5000 BP. About 10% of the stored sediment is estimated to be of alluvial origin. Most of the sediment is derived by the erosion of the Pleistocene basement during recession of the barriers, but tide-induced crossshore transport from the North Sea forms an additional source for the barriers and back-barriers of the west-facing coast of the Netherlands.
Till and moraine emplacement in a deforiting bed surge -an example from a marine environment Boulton, G.S.; van der Meer, J.J.M.; Hart, J.; Beets, D.; Ruegg, G.H.J.; Wateren, F.M.; Jarvis, J. Published in:Quaternary Science Reviews DOI:10.1016/0277-3791(95) Link to publication Citation for published version (APA):Boulton, G. S., van der Meer, J. J. M., Hart, J., Beets, D., Ruegg, G. H. J., Wateren, F. M., & Jarvis, J. (1996). Till and moraine emplacement in a deforiting bed surge -an example from a marine environment. Quaternary Science Reviews, 15, 961-987. DOI: 10.1016/0277-3791(95)00091-7 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 10 May 2018Quaternary Science Reviews, Vol. 15, pp. 961-987, 1996. PergamonCopyright © 1996 Elsevier Science Ltd. Printed in Great Britain. All rights reserved. 0277-3791(95) Abstract --The glacier Sefstrombreen in Spitsbergen surged across an arm of the sea between QSR 1882 and 1886 and rode up onto the island Coraholmen. Marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location, transported, and smeared over the sea bed and ~ Coraholmen as a deformation till. The glacier emplaced about 210Sm ~ (0.2 km 3) of drift in the terminal 2 km of its advance in a maximum of 14 years, leaving a thickness of up to 20 m on Coraholmen, which was doubled in size as a result.~ ~ During the surge, subglacial muds were characterised by high water pressures, low effective pressures and low frictional resistance to glacier movement. Original sedimentary inhomogenities permit fold structures to be identified, but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills.The surge was probably shortlived, and as the heavily crevassed glacier stagnated, underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface. Reticulate "crevasse-intrusion" ridges on Coraholmen and the sea floor reflect the orientation of surge generated crevasses. Water and sediment was also extruded beyond the glacier at its maximum extent, to form extensive flows producing "till tongues" both on Coraholmen and the sea floor extending over 1.3 km from the glac...
The contact relationships between metabasalts (eclogites, glaucophanites, prasinites, etc.) and the enclosing mica schists in the Venezuelan Coast Ranges favour a common petrological history for both. Mineralogical disequilibria, such as replacement textures and mineral zoning in the metabasic assemblages, can all be related to a single metamorphic cycle. Relict deuteric/late magmatic hornblende epitaxially overgrown by the barroisitic amphibole of this metamorphic event shows that the latter has been the only regional metamorphic episode to have affected these rocks. The high-pressure character of the metamorphism is a logical consequence of overthrusting related to collision of the Aruba-Blanquilla island arc with the South American continental margin. The well-defined stratigraphy and detailed radiometric dating of intrusive rocks in the Netherlands Antilles indicate that this collision took place in the Coniacian/Campanian interval.The igneous rocks of the Netherlands Antilles, which are considered to form part of the colliding arc, consist largely of submarine volcanics, as well as a tonalite/gabbro batholith. These rocks range in age from middle Albian to Coniacian. The volcanics of Curaçao and Aruba are composed of basalts with a MORB chemistry and are oceanic in origin. Nevertheless, these sequences differ from "normal" oceanic crust by their thickness, chemical homogeneity and the non-depleted nature of the source, thus suggesting that they were fed by a prolific chondritic mantle plume. The volcanics of Bonaire range from basalt to rhyolite in composition and are chemically related to the primitive island arc series. An important characteristic is the high initial water content of these magmas, *Present address: Geological Survey of the Netherlands, Spaarne 17, Haarlem, The Netherlands. D. J. Beets and Others as shown by the geometry and mineralogy of the flows. The tonalite/gabbro batholith on Aruba is of calc-alkaline composition. The similarity in chemistry between the volcanics of Bonaire and the Villa de Cura Group of the Venezuelan mainland supports the view that the latter is an overthrust remnant of the colliding arc. Comparison with the metabasalts of the La Rinconada Group of Margarita Island is equivocal.Existing paleomagnetic evidence indicates that the arc underwent a 90° north-south to east-west rotation shortly before collision, and that the colliding arc extended via the Aves Ridge into the Greater Antilles. The age of the oldest volcanics of this arc, and thus the age of its origin, is uncertain. Most data favour formation in the Early Cretaceous, but a Late Jurassic age is also possible. Consequently, two alternative models for the evolution of the arc are proposed: one in which the arc forms as a lengthening Central American "isthmus" in response to opening of the Caribbean in the Late Jurassic, and a second in which the arc originates in the Pacific in the Early Cretaceous. In order to collide with the northern as well as southern margin of the Caribbean, the arc must have lengthened...
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