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SANDRA PASSCHIER CEES LABAN CHRIS S. MESDAG KENNETH F. RIJSDIJK 《Boreas: An International Journal of Quaternary Research》2010,39(3):633-647
Passchier, S., Laban, C., Mesdag, C.S. & Rijsdijk, K.F. 2010: Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea. Boreas, Vol. 39, pp. 633–647. 10.1111/j.1502‐3885.2009.00138.x. ISSN 0300‐9483. Changes in subglacial bed conditions through multiple glaciations and their effect on ice dynamics are addressed through an analysis of glacigenic sequences in the Upper Pleistocene stratigraphy of the southern North Sea basin. During Elsterian (MIS 12) ice growth, till deposition was subdued when ice became stagnant over a permeable substrate of fluvial sediments, and meltwater infiltrated into the bed. Headward erosion during glacial retreat produced a dense network of glacial valleys up to several hundreds of metres deep. A Saalian (MIS 6) glacial advance phase resulted in the deposition of a sheet of stiff sandy tills and terminal moraines. Meltwater was at least partially evacuated through the till layer, resulting in the development of a rigid bed. During the later part of the Saalian glaciation, ice‐stream inception can be related to the development of a glacial lake to the north and west of the study area. The presence of meltwater channels incised into the floors of glacial troughs is indicative of high subglacial water pressures, which may have played a role in the onset of ice streaming. We speculate that streaming ice flow in the later part of the Saalian glaciation caused the relatively early deglaciation, as recorded in the Amsterdam Terminal borehole. These results suggest that changing subglacial bed conditions through glacial cycles could have a strong impact on ice dynamics and require consideration in ice‐sheet reconstructions. 相似文献
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CEES VAN der LAND FURU MIENIS HENK DE HAAS NORBERT FRANK RUDY SWENNEN TJEERD C. E. VAN WEERING 《Sedimentology》2010,57(3):912-931
Cold water coral covered carbonate mounds at the south‐west margin of the Rockall Trough form ridges several kilometres long and up to 380 m high. Piston cores obtained at three mound crests reveal the complex internal structure of the mound build up, with alternating unlithified coral‐dominated intervals and lithified intervals. The most recent lithified interval is covered by corals embedded in a fine‐grained matrix, comprising ca 11 000 years of continuous mound evolution. Before this time 230Th/U dating shows the presence of several hiatuses in mound build‐up. Aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth. Downcore X‐ray fluorescence scanning, computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration. The upper boundary of the most recent lithified interval shows some erosional features, but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long‐term non‐sedimentation, but to earlier sub‐surface diagenesis. Organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons. Depending on the openness of the system, this can lead to precipitation of a more stable low‐magnesium carbonate. A model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals. 相似文献
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FREEK S. BUSSCHERS RONALD T. VAN BALEN KIM M. COHEN CEES KASSE HENK J. T. WEERTS JAKOB WALLINGA FRANS P. M. BUNNIK 《Boreas: An International Journal of Quaternary Research》2008,37(3):377-398
A new reconstruction of the interaction between the Saalian Drente glaciation ice margin and the Rhine–Meuse fluvial system is presented based on a sedimentary analysis of continuous core material, archived data and a section in an ice-pushed ridge. Optically Stimulated Luminescence (OSL) was applied to obtain independent age control on these sediments and to establish a first absolute chronology for palaeogeographical events prior to and during the glaciation. We identified several Rhine and Meuse river courses that were active before the Drente glaciation (MIS 11-7). The Drente glaciation ice advance into The Netherlands (OSL-dated to fall within MIS 6) led to major re-arrangement of this drainage network. The invading ice sheet overrode existing fluvial morphology and forced the Rhine–Meuse system into a proglacial position. During deglaciation, the Rhine shifted into a basin in the formerly glaciated area, while the Meuse remained south of the former ice limit, a configuration that persisted throughout most of the Eemian and Weichselian periods. An enigmatic high position of proglacial fluvial units and their subsequent dissection during deglaciation by the Meuse may partially be explained by glacio-isostatic rebound of the area, but primarily reflects a phase of high base level related to a temporary proglacial lake in the southern North Sea area, with lake levels approximating modern sea levels. Our reconstruction indicates that full 'opening' of the Dover Strait and lowering of the Southern Bight, enabling interglacial marine exchange between the English Channel and the North Sea, is to be attributed to events during the end of MIS 6. 相似文献
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Distribution and dispersal pattern of clay minerals in surface sediments, eastern Beibu Gulf, South China Sea 总被引：3，自引：2，他引：1
Clay minerology of sediments are useful in determining distribution,sources and dispersal routes of fine-grained sediments.In the present paper,clay minerals of surface sediments throughout the eastern part of Beibu Gulf has been investigated to reveal sources and transport of detrital finegrained sediments.Four distinct clay mineral suites were observed from cluster analysis of clay mineral compositions of the samples.From the distribution pattern of clay minerals,we conclude that kaolinte in the eastern gulf is mainly derived from South China Landmass;Smectite could not be transported mainly by surface current from north-western Hainan Island,and maybe minor portion of it from Red River;Illite is mainly transported by the currents from South China Sea.Chlorite has two sources,namely South China Sea and South China Landmass.The Zhujiang River derived sediments could not be one of the sources for the clay mineral here,because of very different composition and ratios.The distribution pattern of clay minerals in the eastern Beibu Gulf is mainly controlled by fine-grained sediment source and local currents.The Silt/Clay,Smectite/Kaolinte,and Smetite/(Chlorite+Illite) ratios could be used as indicators of fine-grained sediment dispersal in the gulf. 相似文献
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