Response of unconfined turbidity current to normal‐fault topography          下载免费PDF全文

Zhiyuan Ge  Wojciech Nemec  Rob L. Gawthorpe  Ernst W.M. Hansen 《Sedimentology》2017,64(4):932-959

Turbidity currents descending the slopes of deep‐water extensional basins or passive continental margins commonly encounter normal‐fault escarpments, but such large‐magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory. This study uses advanced computational fluid dynamics numerical simulations to monitor the response of large, natural‐scale unconfined turbidity currents (100 m thick and 2000 m wide at the inlet gate) to normal‐fault topography with a maximum relief of nearly 300 m. For comparative purposes, the turbidity current is first released on a non‐faulted pristine slope of 1·5° (simulation model 1). The expanding and waxing flow bypasses the slope without recognizable deposition within the visibility limit of 8 vol.% sand grain packing. Similar flow is then released towards the tip (model 2) and towards the centre (model 3) of a normal‐fault escarpment. In both of these latter models, the sand carried by flow tends to be entrapped in four distinct depozones: an upslope near‐gate zone of flow abrupt expansion and self‐regulation; a flow‐transverse zone at the fault footwall edge; a flow‐transverse zone at the immediate hangingwall; and a similar transverse zone near the crest of the hangingwall counter‐slope, where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow. The near‐bottom reverse flow appears to be generated on a counter‐slope of 1·1°, increased to 2·0° by deposition. The Kelvin–Helmholtz interface instability plays an important role by causing three‐dimensional fluctuations in the flow velocity magnitude and sediment concentration. The thick deposits of large single‐surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows. The study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope‐fan conceptual models when it comes to the spatial prediction of main sand depozones.  相似文献   

Orientation information in wayfinding instructions: evidences from human verbal and visual instructions     

Vanessa Joy A. Anacta  Angela Schwering  Rui Li  Stefan Muenzer 《GeoJournal》2017,82(3):567-583

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Magnetostratigraphic correlation of the Oxfordian–Kimmeridgian boundary     

Piotr A. Przybylski  James G. Ogg  Andrzej Wierzbowski  Angela L. Coe  Mark W. Hounslow  John K. Wright  François Atrops  Erik Settles 《Earth and Planetary Science Letters》2010,289(1-2):256-272

A magnetic polarity pattern for Boreal and Sub-Boreal ammonite zones of the Upper Oxfordian to Lower Kimmeridgian was established and confirmed in four British sections, including the proposed Global Boundary Stratotype Section and Point (GSSP) on the Isle of Skye (Scotland) to define the base of the international Kimmeridgian Stage. A coeval pattern for Sub-Mediterranean ammonite zones was compiled from seven sections in Poland, one German section and multi-section composites from France and Spain. The mean paleopole for the European Craton (excluding Spain) at the Oxfordian–Kimmeridgian boundary is 74.2°N, 181.3°E (Α₉₅ = 3.8°). The common magnetic polarity scale enables inter-correlation of ammonite subzones among these three faunal provinces and to the marine magnetic-anomaly M-Sequence. The proposed GSSP at the base of the Pictonia baylei Zone is near the base of an extended interval dominated by reversed polarity, which is interpreted to be Chron M26r. This GSSP level projects to the lower to middle part of the Epipeltoceras bimammatum Subzone, which is the middle subzone of this E. bimammatum Zone in the Sub-Mediterranean standard zonation. In contrast, the traditional placement of the Oxfordian–Kimmeridgian boundary in that Sub-Mediterranean standard zonation (base of Sutneria platynota Zone) is at the base of Chron M25r, or nearly 1 million years younger.  相似文献   

Late Glacial ice advances in southeast Tibet     

Stefan Strasky  Angela A. Graf  Zhizhong Zhao  Peter W. Kubik  Heinrich Baur  Christian Schlüchter  Rainer Wieler 《Journal of Asian Earth Sciences》2009,34(3):458-465

The sensitivity of Tibetan glacial systems to North Atlantic climate forcing is a major issue in palaeoclimatology. In this study, we present surface exposure ages of erratic boulders from a valley system in the Hengduan Mountains, southeastern Tibet, showing evidence of an ice advance during Heinrich event 1. Cosmogenic nuclide analyses (¹⁰Be and ²¹Ne) revealed consistent exposure ages, indicating no major periods of burial or pre-exposure. Erosion-corrected (3 mm/ka) ¹⁰Be exposure ages range from 13.4 to 16.3 ka. This is in agreement with recalculated exposure ages from the same valley system by [Tschudi, S., Schäfer, J.M., Zhao, Z., Wu, X., Ivy-Ochs, S., Kubik, P.W., Schlüchter, C., 2003. Glacial advances in Tibet during the Younger Dryas? Evidence from cosmogenic ¹⁰Be, ²⁶Al, and ²¹Ne. Journal of Asian Earth Sciences 22, 301–306.]. Thus this indicates that local glaciers advanced in the investigated area as a response to Heinrich event 1 cooling and that periglacial surface adjustments during the Younger Dryas overprinted the glacial morphology, leading to deceptively young exposure ages of certain erratic boulders.  相似文献   

Kandidater udgået fra Københavns Universitets Geografiske Institut 1966–71     

Viggo Hansen  Niels Nielsen  Ruth Helkiær Jensen  Kaf Hansen  Kaj Hansen  Johannes Krüger 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):91-100

Christensen, Leif: Faststående og omlejrede Saale-morånelersaflejringer. Et eksempel fra Szdding-området, Vestjylland. Geografisk Tidsskrift 82: 91–94. Copenhagen, Dec. 1, 1982.

In situ clayey till materials on the Skovbjerg Bakkea, western Jutland can be recognized by crop-marks revealing pseudomorphs of ice-wedge polygons in orthogonal, random orthogonal and hexagonal patterns. The tills inside these polygonal patterns have high shear-strength values as measured by vane tests. Remoulded fossil solifluction deposits of till origin reveal stripes and deformed polygonal patterns in the crops. High strength as measured by vane are encountered below fossil solifluction deposits 4 meters below ground.  相似文献   

Anmeldelser     

Niels Nielsen  Viggo Hansen  Kaj Hansen  Kr. M. Jensen  Sten Folving  Sofus Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):101-118

Meyer, Marlene: Settlement Patterns and Land-use in Northern Ghana—A Study of the Changes during the period 1963–1991 based on Historical Surveys and recent SPOT-images. Geografisk Tidsskrift 92:101–104. Copenhagen 1992.

A study by Hunter (1966) describes how large areas along the Red Volta River bank, have been abandoned due to river blindness. The mapping of current land-use status and settlements patterns, using multispectral SPOT-satellite images, shows how the border of settlements continue to retreat, whereas new land is being reclaimed for bush fields in the abandoned areas.  相似文献   

A Compilation of Radiocarbon Dates from Disko Bugt,Central West Greenland/Meteorological Observations in 1996 at the Arctic Station,Qeqertarsuaq (Godhavn), Central West Greenland/A Discussion on Pingos in Mellemfjord,Disko, Central West Greenland/Open System Pingos in Mellemfjord,Disko, Central West Greenland: A Reply to Gurney and Worsley     

Morten Rasch  Birger Hansen  Ole Humlum  Niels Nielsen  Peter Funch  Stephen D. Gurney 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):143-159

188 new and previously published radiocarbon dates on Holocene material from Disko Bugt, central West Greenland, are presented together with relevant informations (laboratory number, place name, dated material, geografic coordinates, altitude and δ¹³C-value) about the dates.

In October 1990 an automatic weather station was established at the Arctic station (65 °15′N,53 °31′W), Qeqertarsuaq (Godhavn), Central West Greenland. The Station register parameters each 20 min., and the parameters have been described in an earlier paper in this journal by Nielsen et al. (1995). The present paper summarises main points of the climate during 1996.

Open system, or more correctly, hydraulic pingos, are genetically poorly understood. A continuing problem concerns their need for a perennial groundwater supply (intra- or sub-permafrost). This has to be maintained despite the existence of continuous permafrost in many areas where they are located. Recent work on Disko Island has suggested a new type of hydraulic pingo developing only in a “marsh environment”. It is argued that the marsh setting is not relevant to the formation of these features and that they are simply hydraulic pingos.

Abstract

A group of marsh initiated open system pingo remnants from the Iterdlagssûp kûgssua valley mouth, in Mellemfjord, Disko Island, Central West Greenland was described in Christiansen (1995). Gurney and Worsley (1997) state that the location of this group of pingo remnants in the Iterdlagssûp kûgssua valley mouth is of no relevance to their genesis, and that they presumably were the result of an assumed late Holocene sea level regression, causing permafrost to be established in the valley bottom. In this reply the arguments by Gurney and Worsley (1997) on the Iterdlagssûp kûgssua valley pingos are commented, and it is argued by way of sea level information, frost penetration and water supply that the special setting must indeed have caused pingo initiation and growth. Furthermore, the area has experienced a relative sea level rise during the late Holocene.  相似文献   

Meteorological Observations 2002 at the Arctic Station,Qeqertarsuaq (69°15'N), Central West Greenland     

Birger Ulf Hansen  Ole Humlum  Niels Nielsen  Dorte P. Lundqvist  Ditte L. Jansen  Christian Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):93-109

An automatic meteorological station has been operating at the Arctic Station (69°15'N, 53°31'W) in West Greenland since 1990. This paper summarises meteorological parameters during 2002, including snow cover, ground temperatures and active layer development, and air temperatures at the Station during the last 12 years are compared to large scale trends during the last century.

A compilation of 93 sedimentation rate determinations based on ²¹⁰Pb dating has been carried out for the North Sea-Baltic Sea transition area from a database containing 165 determinations carried out by Danish institutions. In the depositional parts of the area sedimentation rates generally range 25–6403 g m^?2 y^?1. An extreme rate of 13351 g m^?2 y^?1 is observed on a station in the Skagerrak. Sedimentation rates significantly increase with depth indicating that the Skagerrak and northern parts of the Kattegat as well as the deep basins in the Baltic Sea act as depocentres for fine-grained sediments. Apparently, sedimentation rates have increased in recent years.  相似文献   

Induced seismicity during the construction of the Gotthard Base Tunnel, Switzerland: hypocenter locations and source dimensions     

Stephan Husen  Edi Kissling  Angela von Deschwanden 《Journal of Seismology》2013,17(1):63-81

A series of 112 earthquakes was recorded between October 2005 and August 2007 during the excavation of the MFS Faido, the southernmost access point of the new Gotthard Base Tunnel. Earthquakes were recorded at a dense network of 11 stations, including 2 stations in the tunnel. Local magnitudes computed from Wood?CAnderson-filtered horizontal component seismograms ranged from ?1.0 to 2.4; the largest earthquake was strongly felt at the surface and caused considerable damage in the tunnel. Hypocenter locations obtained routinely using a regional 3-D P-wave velocity model and a constant Vp/Vs ratio 1.71 were about 2?km below the tunnel. The use of seismic velocities calibrated from a shot in the tunnel revealed that routinely obtained hypocenter locations were systematically biased to greater depth and are now relocated to be on the tunnel level. Relocation of the shot using these calibrated velocities yields a location accuracy of 25?m in longitude, 70?m in latitude, and 250?m in focal depth. Double-difference relative relocations of two clusters with highly similar waveforms showed a NW?CSE striking trend that is consistent with the strike of mapped faults in the MFS Faido. Source dimensions computed using the quasidynamic model of Madariaga (Bull Seismo Soc Am 66(3):639?C666, 1976) range from 50 to 170?m. Overlapping source dimensions for earthquakes within the two main clusters suggests that the same fault patch was ruptured repeatedly. The observed seismicity was likely caused by stress redistribution due to the excavation work in the MFS Faido.  相似文献   

Inverse problems with non-trivial priors: efficient solution through sequential Gibbs sampling   总被引：1，自引：0，他引：1  

Thomas Mejer Hansen  Knud Skou Cordua  Klaus Mosegaard 《Computational Geosciences》2012,16(3):593-611

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