Provenance and depositional environments of Quaternary sediments from the western North Sea Basin     

Bethan J. Davies  David H. Roberts  David R. Bridgland  Colm Ó Cofaigh  James B. Riding 《第四纪科学杂志》2011,26(1):59-75

As the majority of the data on Quaternary sediments from the North Sea Basin are seismostratigraphical, we analysed the Elsterian Swarte Bank Formation, the Late Saalian Fisher Formation and the Late Weichselian (Dimlington Stadial) Bolders Bank Formation in order to determine genesis and provenance. The Swarte Bank Formation is a subglacial till containing palynomorphs from the Moray Forth and the northeastern North Sea, and metamorphic heavy minerals from the Scottish Highlands. The Fisher Formation was sampled from the northern and central North Sea. In the north, it is interpreted as a subglacial till, with glaciomarine sediments cropping out further south. These sediments exhibit a provenance signature consistent with the Midland Valley of Scotland, the Eocene of the North Sea Basin, the Grampian Highlands and northeast Scotland. The Bolders Bank Formation is a subglacial till containing palynomorphs from the Midland Valley of Scotland, northern Britain, and a metamorphic heavy‐mineral suite indicative of the Grampian Highlands, Southern Uplands and northeast Scotland. These data demonstrate that there was repeated glaciation of the North Sea Basin during the Middle and Late Pleistocene, with ice sheets originating in northern Scotland. There was no evidence for a Scandinavian ice sheet in the western North Sea basin. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Chronological and palaeoenvironmental context of human occupations at the Buendía rockshelter (Central Spain) during the late Upper Pleistocene in inland Iberia          下载免费PDF全文

IGNACIO DE LA TORRE  ROSA MARÍA ALBERT  ETHEL ALLUÉ  ESTEBAN ÁLVAREZ‐FERNÁNDEZ  M.TERESA APARICIO  ADRIÁN ARROYO  ALFONSO BENITO‐CALVO  MARÍA JOSÉ GIL GARCÍA  ELÍAS LÓPEZ‐ROMERO  NORAH MOLONEY  M. BLANCA RUIZ ZAPATA  PALMIRA SALADIÉ 《第四纪科学杂志》2015,30(4):376-390

  相似文献   

ANALYTICAL SOLUTIONS FOR CUSP RESONANCE IN DISSIPATIVE MHD     

ERDÉLYI  RÓBERT 《Solar physics》1997,171(1):49-59

The present paper considers resonant slow waves in 1D non-uniform magnetic flux tubes in dissipative MHD. Analytical solutions are obtained for the Lagrangian displacement and the Eulerian perturbation of the total pressure for both static and stationary equilibrium states. From these analytical solutions we obtain the fundamental conservation law and the jump conditions for resonant slow waves in dissipative MHD. The validity of the ideal conservation law and jump conditions obtained by Sakurai, Goossens, and Hollweg (1991) for static equilibria and Goossens, Hollweg, and Sakurai (1992) for stationary equilibria is justified in dissipative MHD.  相似文献   

Formation of submarginal and proglacial end moraines: implications of ice‐flow mechanism during the 1963–64 surge of Brúarjökull,Iceland     

ÍVAR ÖRN BENEDIKTSSON  ÓLAFUR INGÓLFSSON  ANDERS SCHOMACKER  KURT H. KJÆR 《Boreas: An International Journal of Quaternary Research》2009,38(3):440-457

The morphology, sedimentology and architecture of an end moraine formed by a ～9 km surge of Brúarjökull in 1963–64 are described and related to ice‐marginal conditions at surge termination. Field observations and accurate mapping using digital elevation models and high‐resolution aerial photographs recorded at surge termination and after the surge show that commonly the surge end moraine was positioned underneath the glacier snout by the termination of the surge. Ground‐penetrating radar profiles and sedimentological data reveal 4–5 m thick deformed sediments consisting of a top layer of till overlying gravel and fine‐grained sediments, and structural geological investigations show that the end moraine is dominated by thrust sheets. A sequential model explaining the formation of submarginal end moraines is proposed. The hydraulic conductivity of the bed had a major influence on the subglacial drainage efficiency and associated porewater pressure at the end of the surge, thereby affecting the rates of subglacial deformation. High porewater pressure in the till decreased its shear strength and raised its strain rate, while low porewater pressure in the underlying gravel had the opposite effect, such that the gravel deformed more slowly than the till. The principal velocity component was therefore located within the till, allowing the glacier to override the gravel thrust sheets that constitute the end moraine. The model suggests that the processes responsible for the formation of submarginal end moraines are different from those operating during the formation of proglacial end moraines.  相似文献   

An international intercalibration for mercury in seawater     

Jón Ólafsson 《Marine Chemistry》1983,13(3):253-254

  相似文献   

Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the north‐east Greenland continental shelf     

Jeffrey Evans  Colm Ó Cofaigh  Julian A. Dowdeswell  Peter Wadhams 《第四纪科学杂志》2009,24(3):279-293

High‐resolution swath bathymetry and TOPAS sub‐bottom profiler acoustic data from the inner and middle continental shelf of north‐east Greenland record the presence of streamlined mega‐scale glacial lineations and other subglacial landforms that are formed in the surface of a continuous soft sediment layer. The best‐developed lineations are found in Westwind Trough, a bathymetric trough connecting Nioghalvfjerdsfjorden Gletscher and Zachariae Isstrøm to the continental shelf edge. The geomorphological and stratigraphical data indicate that the Greenland Ice Sheet covered the inner‐middle shelf in north‐east Greenland during the most recent ice advance of the Late Weichselian glaciation. Earlier sedimentological and chronological studies indicated that the last major delivery of glacigenic sediment to the shelf and Fram Strait was prior to the Holocene during Marine Isotope Stage 2, supporting our assertion that the subglacial landforms and ice sheet expansion in north‐east Greenland occurred during the Late Weichselian. Glacimarine sediment gravity flow deposits found on the north‐east Greenland continental slope imply that the ice sheet extended beyond the middle continental shelf, and supplied subglacial sediment direct to the shelf edge with subsequent remobilisation downslope. These marine geophysical data indicate that the flow of the Late Weichselian Greenland Ice Sheet through Westwind Trough was in the form of a fast‐flowing palaeo‐ice stream, and that it provides the first direct geomorphological evidence for the former presence of ice streams on the Greenland continental shelf. The presence of streamlined subglacially derived landforms and till layers on the shallow AWI Bank and Northwind Shoal indicates that ice sheet flow was not only channelled through the cross‐shelf bathymetric troughs but also occurred across the shallow intra‐trough regions of north‐east Greenland. Collectively these data record for the first time that ice streams were an important glacio‐dynamic feature that drained interior basins of the Late Weichselian Greenland Ice Sheet across the adjacent continental margin, and that the ice sheet was far more extensive in north‐east Greenland during the Last Glacial Maximum than the previous terrestrial–glacial reconstructions showed. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Groundwater problems in the karstic aquifers of the Dobrich region,northeastern Bulgaria     

A. PULIDO-BOSCH  M. LÓPEZ-CHICANO  J. M. CALAFORRA  M. L. CAL VACHE  M. MACHKOVA  D. DIMITROV 《水文科学杂志》2013,58(6):913-927

Abstract

In the Dobrich region, with an area of a little over 4000 km², two important aquifer systems can be differentiated, which we have named the Upper and Deep Aquifers. The hydrodynamic and hydrogeochemical characteristics of these two aquifers are different. Agricultural activities, livestock units, and urban waste waters and solid wastes constitute the principal sources of contamination of the Upper Aquifer. Furthermore, signs of marine intrusion in some coastal zones have been detected. The Deep Aquifer is found to be affected by hydrogeochemical processes related to hydrocarbons that generate elevated concentrations of H₂S and NO₂ (which may exceed 10 mg 1^?1). This aquifer has numerous deep overflowing boreholes that lack appropriate capping, with the consequent loss of resource, draining in the order of 4 m³ s^?1 of thermal and sulphurous waters.  相似文献   

Estevâo Cabral's pioneering contribution to open channel hydrometry     

ANTÓNIO DE CARVALHO QUINTELA 《水文科学杂志》2013,58(3):241-246

Résumé

Le portugais Estevão Cabral (1734–1811) a construit, en 1786, un moulinet lui permettant de mesurer la vitesse de l'eau à différentes profondeurs et de calculer ainsi le débit des rivières. Cabrai a été le premier chercheur qui ait utilisé un moulinet pour mesurer la vitesse de l'eau au-dessous de la surface libre, les moulinets à roue à ailettes planes utilisés auparavant ne pouvant que mesurer la vitesse à la surface. Il a aussi été le premier chercheur à soutenir que la vitesse dans les écoulements a surface libre croît depuis la surface jusqu'à un maximum à partir duquel elle décroît vers le fond.  相似文献   

Dolomite formation within microbial mats in the coastal sabkha of Abu Dhabi (United Arab Emirates)   总被引：1，自引：0，他引：1  

TOMASO R. R. BONTOGNALI  CRISÓGONO VASCONCELOS  ROLF J. WARTHMANN  STEFANO M. BERNASCONI  CHRISTOPHE DUPRAZ  CHRISTIAN J. STROHMENGER  JUDITH A. McKENZIE 《Sedimentology》2010,57(3):824-844

Microbial mediation is the only demonstrated mechanism to precipitate dolomite under Earth surface conditions. A link between microbial activity and dolomite formation in the sabkha of Abu Dhabi has, until now, not been evaluated, even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences. Such an evaluation is the purpose of this study, which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of Abu Dhabi, along a transect from the intertidal to the supratidal zone. This investigation revealed a close association between microbial mats and dolomite, suggesting that microbes are involved in the mineralization process. Observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats. In current models, microbial dolomite precipitation is linked to an active microbial activity that sustains high pH and alkalinity and decreased sulphate concentrations in pore waters. Such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone. By contrast, these models cannot be applied to the supratidal zone, where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity. As no abiotic mechanism is known to form dolomite at Earth surface conditions, two different hypotheses can reconcile this result. In a first scenario, all of the dolomite present in the supratidal zone formed in the past, when the mats were active at the surface. In a second scenario, dolomite formation continues within the buried and inactive mats. In order to explain dolomite formation in the absence of active microbial metabolisms, a revised microbial model is proposed in which the mineral‐template properties of exopolymeric substances play a crucial role.  相似文献   

The action of wind and water in a mid‐Cretaceous subtropical erg‐margin system close to the Variscan Iberian Massif,Spain     

JUAN PEDRO RODRÍGUEZ‐LÓPEZ  NIEVES MELÉNDEZ  POPPE L. De BOER  ANA ROSA SORIA 《Sedimentology》2010,57(5):1315-1356

Aeolian processes and ephemeral water influx from the Variscan Iberian Massif to the mid‐Cretaceous outer back‐erg margin system in eastern Iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements. Remains of aeolian dunes encased in ephemeral fluvial deposits (aeolian pods) demonstrate intense erosion of windblown deposits by sudden water fluxes. The alternating activity of wind and water led to a variety of facies associations such as deflation lags, desert pavements, aeolian dunes, pebbles scattered throughout dune strata, aeolian sandsheets, aeolian deposits with bimodal grain‐size distributions, mud playa, ephemeral floodplain, pebble‐sand and cobble‐sand bedload stream, pebble–cobble‐sand sheet flood, sand bedload stream, debris flow and hyperconcentrated flow deposits. Sediment in this desert system underwent transport by wind and water and reworking in a variety of sub‐environments. The nearby Variscan Iberian Massif supplied quartzite pebbles as part of mass flows. Pebbles and cobbles were concentrated in deflation lags, eroded and polished by wind‐driven sands (facets and ventifacts) and incorporated by rolling into the toesets of aeolian dunes. The back‐erg depositional system comprises an outer back‐erg close to the Variscan highlands, and an inner back‐erg close to the central‐erg area. The inner back‐erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits. In the inner back‐erg area ephemeral wadis, desiccated after occasional floods, were mud cracked and overrun episodically by aeolian dunes. Subsequent floods eroded the aeolian dunes and mud‐cracked surfaces, resulting in largely structureless sandstones with boulder‐size mudstone intraclasts. Floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes. The remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands. Upon desiccation, deflation resulted in lags of coarser‐grained sediments. A renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions. Synsedimentary tectonics caused the outer back‐erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands. Ephemeral water flow to the outer back‐erg area supplied pebbles, eroded aeolian dunes, and produced hyperconcentrated flow deposits. Fluidization and liquefaction generated gravel pockets and recumbent folds. Dune damming after sporadic rains (the case of the Namib Desert), monsoonal water discharge (Thar Desert) and meltwater fluxes from glaciated mountains (Taklamakan Desert) are three potential, non‐exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the Cretaceous desert margin system. An increase in relief driven by the Aptian anti‐clockwise rotation of Iberia, led to an altitude sufficient for the development of orographic rains and snowfall which fed (melt)water fluxes to the desert margin system. Quartzite conglomerates and sands, dominantly consisting of quartz and well‐preserved feldspar grains which are also observed in older Cretaceous strata, indicate an arid climate and the mechanical weathering of Precambrian and Palaeozoic metamorphic sediments and felsic igneous rocks. Unroofing of much of the cover of sedimentary rocks in the Variscan Iberian Massif must therefore have taken place in pre‐Cretaceous times.  相似文献