The Record of an Extreme Flood in the Sediments of Montane Lillooet Lake, British Columbia: Implications for Paleoenvironmental Assessment     

Robert Gilbert  Sarah Crookshanks  Kyle R. Hodder  John Spagnol  Roland B. Stull 《Journal of Paleolimnology》2006,35(4):737-745

Severe rainfall in mid October, 2003 produced the largest floods in almost a century of record on rivers in the Cordillera of southwestern British Columbia. Sediment deposited in Lillooet Lake as a result of this event is clearly distinguished by stratigraphy, colour, texture, magnetic properties, and organic content. Each of these physical properties is related to the lacustrine processes, especially turbid underflow, that distributed the sediment through the lake. The flood, which lasted less than a week, delivered 8–12 times the amount of sediment that accumulates in most entire years in the deepest, central parts of the lake. Recognition of events of this type in the stratigraphic record offers a means of assessing the changing nature of extreme hydroclimatic events, and their relation to more ubiquitous, lower-energy processes.  相似文献   

A highlight of environmental and engineering geology in Fargo, North Dakota, USA     

Fred J. Anderson 《Environmental Geology》2006,49(7):1034-1042

Several unfavorable environmental and engineering geologic conditions exist in Fargo, North Dakota. Dominantly, the behavior of smectitic clays within the proglacial Lake Agassiz sediments of the Sherack and Brenna Formations creates subsoil instability beneath engineered structures in the Fargo area and slope instability within cutbank meanders of the Red River of the North. Unfavorable engineering geologic conditions encountered include: the elastic deformation of clayey glaciolacustrine soils, shrink-swell properties, inadequate bearing capacities, and mass movements. These conditions are responsible for structural failures including the Fargo Grain Elevator in 1955 and the Northern Pacific railroad grade. Bank failures along the Red River are common due to the inherent instability of Brenna Formation smectitic clays which are subject to plastic deformation in the subsurface, with resultant block failure of overlying Sherack Formation. Recent alluvial sediments due to typical fluvial action and the continued seasonal saturation of cutbank meanders within the floodplain also add to soil instability.  相似文献   

Groundwater flow and velocity in a 500 ka pre-Illinoian till, eastern Iowa     

K. E. Schilling  S. Tassier-Surine 《Environmental Geology》2006,50(8):1255-1264

Few hydrology studies have investigated glacial till older than Illinoian time (> 300,000 BP) despite these older tills overlying a large portion of North America. An 8- and 6-well monitoring well nest installed into a 31 m thick pre-Illinoian till sequence near Cedar Rapids, Iowa was characterized using traditional hydrologic methods and chemical tracers. The aquitard system consists of about 9 m of fine-grained oxidized pre-Illinoian till overlying 22 m of unoxidized till and Devonian dolomite bedrock. Hydraulic conductivity ranged from 10⁻⁷ m/s in oxidized till and 10⁻¹⁰ m/s in unoxidized till. Hydraulic head relations indicated downward groundwater flow through the till profile with hydraulic gradients steepest near the unoxidized till/bedrock interface. Tritium and nitrate concentrations indicated recent (< 50 years old) recharge to a depth of 9–12 m below land surface. ¹⁸O and ²H results ranged between −6.2 to −7.9% and −38.0 to −50.9%, respectively, and plotted near the local Meteoric Water Line. A 1 per mil shift toward less negative ¹⁸O values with depth may suggest a climate change signal contained in the till water but more data are needed to verify this trend. Vertical groundwater velocity through the unoxidized till was estimated to range from 0.4 to 5.7 cm/year. The thickness of unoxidized pre-Illinoian till in Linn County was estimated from available records and contoured against vertical travel times to evaluate the effectiveness of pre-Illinoian till in preventing nitrate migration to underlying bedrock aquifers.  相似文献   

Proglacial Sediment—Landform Associations of a Polythermal Glacier: Storglaciären, Northern Sweden     

James L. Etienne  Neil F. Glasser  Michael J. Hambrey 《Geografiska Annaler: Series A, Physical Geography》2003,85(2):149-164

Mapping and laboratory analysis of the sediment—landform associations in the proglacial area of polythermal Storglaciären, Tarfala, northern Sweden, reveal six distinct lithofacies. Sandy gravel, silty gravel, massive sand and silty sand are interpreted as glaciofluvial in origin. A variable, pervasively deformed to massive clast‐rich sandy diamicton is interpreted as the product of an actively deforming subglacial till layer. Massive block gravels, comprising two distinctive moraine ridges, reflect supraglacial sedimentation and ice‐marginal and subglacial reworking of heterogeneous proglacial sediments during the Little Ice Age and an earlier more extensive advance. Visual estimation of the relative abundance of these lithofacies suggests that the sandy gravel lithofacies is of the most volumetric importance, followed by the diamicton and block gravels. Sedimentological analysis suggests that the role of a deforming basal till layer has been the dominant factor controlling glacier flow throughout the Little Ice Age, punctuated by shorter (warmer and wetter climatic) periods where high water pressures may have played a more important role. These results contribute to the database that facilitates discrimination of past glacier thermal regimes and dynamics in areas that are no longer glacierized, as well as older glaciations in the geological record.  相似文献   

Figure 1 Linear fitness of the index H' respectively calculated by the number or the area of the related Sus Pedodiversity analysis in Hainan Island     

ZHANG Xuelei  CHEN Jie  ZHANG Ganlin  TAN Manzhi  J.J. Ibá  ?ez 《地理学报》2003,13(2):181-186

  相似文献   

Record of Late Pleistocene Glaciation and Deglaciation in the Southern Cascade Range. I. Petrological Evidence from Lacustrine Sediment in Upper Klamath Lake, Southern Oregon     

Richard L. Reynolds  Joseph G. Rosenbaum  Josh Rapp  Michael W. Kerwin  J. Platt Bradbury  Steven Colman  David Adam 《Journal of Paleolimnology》2004,31(2):217-233

Petrological and textural properties of lacustrine sediments from Upper Klamath Lake, Oregon, reflect changing input volumes of glacial flour and thus reveal a detailed glacial history for the southern Cascade Range between about 37 and 15 ka. Magnetic properties vary as a result of mixing different amounts of the highly magnetic, glacially generated detritus with less magnetic, more weathered detritus derived from unglaciated parts of the large catchment. Evidence that the magnetic properties record glacial flour input is based mainly on the strong correlation between bulk sediment particle size and parameters that measure the magnetite content and magnetic mineral freshness. High magnetization corresponds to relatively fine particle size and lower magnetization to coarser particle size. This relation is not found in the Buck Lake core in a nearby, unglaciated catchment. Angular silt-sized volcanic rock fragments containing unaltered magnetite dominate the magnetic fraction in the late Pleistocene sediments but are absent in younger, low magnetization sediments. The finer grained, highly magnetic sediments contain high proportions of planktic diatoms indicative of cold, oligotrophic limnic conditions. Sediment with lower magnetite content contains populations of diatoms indicative of warmer, eutrophic limnic conditions. During the latter part of oxygen isotope stage 3 (about 37–25 ka), the magnetic properties record millennial-scale variations in glacial-flour content. The input of glacial flour was uniformly high during the Last Glacial Maximum, between about 21 and 16 ka. At about 16 ka, magnetite input, both absolute and relative to hematite, decreased abruptly, reflecting a rapid decline in glacially derived detritus. The decrease in magnetite transport into the lake preceded declines in pollen from both grass and sagebrush. A more gradual decrease in heavy mineral content over this interval records sediment starvation with the growth of marshes at the margins of the lake and dilution of detrital material by biogenic silica and other organic matter.  相似文献   

Re-exposed basement landforms in the Disko region, West Greenland — disregarded data for estimation of glacial erosion and uplift modelling   总被引：1，自引：1，他引：1  

Johan M. Bonow   《Geomorphology》2005,72(1-4):106-127

Classifications of large-scale landscapes in Greenland have traditionally been based on type and intensity of glacial erosion, with the general idea that present landforms are mainly the result of erosion from ice sheets and glaciers. However, on southern Disko and in areas offshore in Disko Bugt, a basement surface has preserved remnants of weathered gneiss and pre-Paleocene landforms, recently exhumed from Paleocene basalt. Isolated hills and lineaments have been mapped in a digital terrain model and aerial photographs. Offshore have hills been mapped from seismic lines. The medium size bedrock forms on southern Disko as tors, clefts and roche moutonées have been studied in the field. Remnant saprolites were inventoried, sampled and analysed according to grain size and clay mineralogy. The basement surface retains saprolites up to 8 m thick in close relation to the cover rocks. The landforms in the basement rocks belong essentially to an etched surface only slightly remodelled by glacial erosion and, below the highest coastline, also by wave action. The outline of hills is governed by two lineament directions, ENE–WSW representing the schistocity of the gneiss and NW–SE fracture zones. These structures are thus interpreted to have been exploited by the deep weathering while the frequent N–S lineaments have not and thus might be younger. Main ice-flow has been from the NE and has resulted in plucking of SW facing lee sides, however the resulting bedrock forms are mainly controlled by structures and orientation of joints. The identification of re-exposed sub-Paleocene etch forms on Disko and the hills of similar size offshore, forming a hilly relief, have implications for identification of a hilly relief south of Disko Bugt, its relation to younger planation surfaces as well as for conclusions of uplift events.  相似文献   

Influence of the Neotethys rifting on the development of the Dampier Sub-basin (North West Shelf of Australia), highlighted by subsidence modelling     

Laurent Langhi  Gilles D. Borel 《Tectonophysics》2005,397(1-2):93

During the Late Palaeozoic and the Mesozoic, the development and evolution of the North West Shelf of Australia have been mostly driven by rifting phases associated with the break-up of Gondwana. These extensional episodes, which culminated in the opening of the Neotethys Ocean during the Permo-Carboniferous and a series of abyssal plains during the Jurassic-Cretaceous, are characterised by different stress regimes and modes of extension, and therefore had distinctive effects on the margin, and particularly on the Northern Carnarvon Basin.Interpretation of 3D and 2D seismic data enables a structural and stratigraphic analysis of the Late Palaeozoic sediments deposited in the proximal part of the Dampier Sub-basin (Mermaid Nose). Based on their seismic characters, stratigraphic relationship, internal patterns, lateral continuity, and architecture, these units are associated here with the Pennsylvanian?–Early Sakmarian glaciogenic Lyons Group and the Sakmarian–Artinskian Callytharra Formation. The former were deposited in a half-graben whose development is associated with the onset of the Neotethys rifting, and the latter is characterised by restricted deposition, inversion of prograding patterns, and uplift.The integration of seismo-stratigraphic characterisation of the Late Palaeozoic sequences and Mesozoic data from one exploration well (Roebuck-1) enables the construction of subsidence curves for the Mermaid Nose and the interpretation of its geohistory.The tectonic subsidence curves show a striking Permo-Carboniferous rifting phase related to the Neotethys rifting and a discrete Late Jurassic–Early Cretaceous event coeval with the opening and the spreading of the Argo Abyssal Plain.This result points out the predominance of the effects of the Permo-Carboniferous Neotethys episode, whereas the extension related to the Argo Abyssal Plain rifting that occurred later and closer to the studied area, had only limited effects on the subsidence of the proximal Dampier Sub-basin. Therefore, it supports a tectonic model with two distinct modes of extension for the Late Palaeozoic (widespread) and the Mesozoic (localised) rifting phases.  相似文献   

Some considerations concerning seismic geomorphology and paleoseismology   总被引：3，自引：1，他引：3  

F. Dramis  A.M. Blumetti   《Tectonophysics》2005,408(1-4):177

Seismic geomorphology studies landforms which developed in connection with earthquakes. Among them, two different end members may be distinguished: 1) seismo-tectonic landforms, including surface faults and fractures, land uplift and subsidence at different scales, surface bulges, elongate ridges, and any other permanent ground deformations directly related to tectonic stress, and 2) seismo-gravitational landforms, such as landslides, deep-seated gravitational slope deformations, sinkholes, and fissures due to sediment compaction or liquefaction and sand blows, connected with both seismic shaking and gravitational stress.A clear-cut distinction between the two categories of landforms is not always easy to make (and in many instances not really useful), while there are, in many cases, ground effects that might be (and should be) considered as simultaneous combinations of seismo-tectonic and seismo-gravitational processes. This applies especially to surface fracturing and faulting which could be the combined result of tectonic stress, stress produced by seismic shaking, and gravitational stress.The objective of this paper is to review selected case histories mainly from Italy and the Mediterranean region, in order to show the importance of a comprehensive study of earthquake-generated landforms for understanding the seismicity level of the area under investigation. We argue that in earthquake prone areas, seismic landforms often constitute typical patterns (seismic landscapes) whose recognition, mapping and paleoseismological analysis may help in the evaluation of seismic hazards.  相似文献   

Environmental changes over the past 25 000 years in the southern Middle Atlas,Morocco          下载免费PDF全文

Jalal Tabel  Carla Khater  Ali Rhoujjati  Laurent Dezileau  Ilham Bouimetarhan  Matthieu Carre  Laurence Vidal  Abdelfattah Benkaddour  Majda Nourelbait  Rachid Cheddadi 《第四纪科学杂志》2016,31(2):93-102

  相似文献