New insights into Late Pleistocene glacial and postglacial history of northernmost Ungava (Canada) from Pingualuit Crater Lake sediments     

Hervé Guyard  Guillaume St-Onge  Reinhard Pienitz  Pierre Francus  Bernd Zolitschka  Garry K.C. Clarke  Sonja Hausmann  Veli-Pekka Salonen  Patrick Lajeunesse  Grégoire Ledoux  Michel Lamothe 《Quaternary Science Reviews》2011,30(27-28):3892-3907

The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS ¹⁴C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850–5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (～4200–600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.  相似文献   

Chronology and palaeoenvironmental implications of the ice‐wedge pseudomorphs and composite‐wedge casts on the Magdalen Islands (eastern Canada)          下载免费PDF全文

Audrey M. Rémillard  Bernard Hétu  Pascal Bernatchez  Jan‐Pieter Buylaert  Andrew S. Murray  Guillaume St‐Onge  Martin Geach 《Boreas: An International Journal of Quaternary Research》2015,44(4):658-675

The Magdalen Islands are a valuable terrestrial record, evidencing the complex glacial and periglacial history of the Gulf of St. Lawrence. Thirteen structures interpreted as ice‐wedge pseudomorphs or composite‐wedge casts were observed at four sites on the southern Magdalen Islands and testify to the former presence of permafrost under periglacial conditions. These features truncate Carboniferous sandstone or Last Glacial Maximum (LGM) glacial and glaciomarine diamicts, both overlain by subtidal or coastal units. Six optically stimulated luminescence (OSL) and four radiocarbon ages were obtained from both host and infilled sedimentary units. These ages provide the first absolute chronological data on these structures, shedding new light on the relationships between glacial and periglacial phases. Our chronostratigraphic data suggest that, after the deglaciation and the emersion of the archipelago, thermal contraction cracks grew during the cold period of the Younger Dryas (11–10 ka; 12.9–11.5 cal. ka BP). The Younger Dryas, which is well documented in the Maritime Provinces of Canada, occurred after a pedogenesis phase associated with the Allerød warm period evidenced by the well‐developed palaeopodzol ubiquitous on the Magdalen Islands.  相似文献   

Holocene palaeoceanographic changes in Barrow Strait,Canadian Arctic: foraminiferal evidence     

Thomas R. Gregory  Christopher W. Smart  Malcolm B. Hart  Guillaume Massé  Lindsay L. Vare  Simon T. Belt 《第四纪科学杂志》2010,25(6):903-910

Holocene changes in the benthic and planktic foraminiferal fauna (>63 µm) from a marine sediment core (ARC‐3 Canadian Arctic Archipelago, 74° 16.050′ N, 91° 06.380′ W, water depth 347 m) show that significant environmental and palaeoceanographic variations occurred during the last 10 ka. Foraminiferal assemblages are restricted to the ca. 4.5–10 ka interval as younger samples are mostly barren of foraminifera due to intense carbonate dissolution after ca. 4.5 ka. Foraminiferal assemblages in the ca. 4.5–10 ka interval are dominated by the benthic species Islandiella helenae and Cassidulina reniforme (57% of total), with Elphidium clavatum, Cibicides lobatulus and Buccella frigida also being common in this interval. The dominance of these species indicates a seasonal sea ice regime which is consistent with the occurrence of the sea ice diatom‐derived organic geochemical biomarker IP₂₅ throughout the core. The abundances of C. reniforme and E. clavatum decline upcore; consistent with more frequent mixing of the Barrow Strait water column during the early Holocene. It is likely that the influence of CO₂‐rich Arctic surface water masses have caused an increase in bottom water corrosivity after ca. 8.5 ka, and dissolution has been further enhanced by sea ice‐related processes after ca. 6 ka, concomitant with increased IP₂₅ fluxes. Dissolution is strongest when IP₂₅ fluxes are highest, suggesting a link between the sea ice and benthic systems. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Exhumation controlled by transcurrent tectonics: the Argentera–Mercantour massif (SW Alps)     

Guillaume Sanchez  Yann Rolland  Marc Jolivet  Stéphanie Brichau  Michel Corsini  Andrew Carter 《地学学报》2011,23(2):116-126

  相似文献   

The hydrological performance of a green roof test bed under UK climatic conditions   总被引：2，自引：0，他引：2  

Virginia Stovin  Gianni Vesuviano  Hartini Kasmin 《Journal of Hydrology》2012

  相似文献   

The effect of soil type,meteorological forcing and slope gradient on the simulation of internal erosion processes at the local scale     

Guillaume Nord  Michel Esteves 《水文研究》2010,24(13):1766-1780

Numerical simulation experiments of water erosion at the local scale (20 × 5 m) using a process‐based model [Plot Soil Erosion Model_2D (PSEM_2D)] were carried out to test the effects of various environmental factors (soil type, meteorological forcing and slope gradient) on the runoff and erosion response and to determine the dominant processes that control the sediment yield at various slope lengths. The selected environmental factors corresponded to conditions for which the model had been fully tested beforehand. The use of a Green and Ampt model for infiltration explained the dominant role played by rainfall intensity in the runoff response. Sediment yield at the outlet of the simulated area was correlated positively with rainfall intensity and slope gradient, but was less sensitive to soil type. The relationship between sediment yield (soil loss per unit area) and slope length was greatly influenced by all environmental factors, but there was a general tendency towards higher sediment yield when the slope was longer. Contribution of rainfall erosion to gross erosion was dominant for all surfaces with slope lengths ranging from 4 to 20 m. The highest sediment yields corresponded to cases where flow erosion was activated. An increase in slope gradient resulted in flow detachment starting upstream. Sediment exported at the outlet of the simulated area came predominantly from the zone located near the outlet. The microrelief helped in the development of a rill network that controlled both the ratio between rainfall and flow erosion and the relationship between sediment yield and slope length. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The field and remote sensing analysis of the Kerguelen Archipelago structure,Indian Ocean     

Lucie Mathieu  Paul Byrne  Damien Guillaume  Benjamin van Wyk de Vries  Bertrand Moine 《Journal of Volcanology and Geothermal Research》2011,199(3-4):206-215

The Kerguelen Archipelago is part of an oceanic plateau with a complex history. Little work has been done on the tectonics of the onshore areas, even though the extensive outcrop renders the islands especially good for structural work. We present the results of three field campaigns and remote sensing analysis carried out in the main Kerguelen Island, around Val Travers valley and Mt Ross volcano (Central Plateau) and in the Rallier du Baty peninsula (SW part of the archipelago). We have mapped faults, fracture sets, and the location and geometry of intrusive bodies. We found that the plateau basalt lavas that make up most of the area are densely fractured, crossed by many veins, dykes and some small faults. This work provides a general framework for the structure of Kerguelen Archipelago that is dominated by 110°-striking faults and veins, dyke swarms and an alignment of recent central volcanoes, which have formed in N-S to NNW-SSE directed extensional stress field. The other structures are fractures, veins and dykes which strike 130–150°, 000° and 030–050°. They are likely related to transform faults of the Indian oceanic crust and to faults of the north Kerguelen Plateau (offshore basement of the archipelago). These buried structures were likely re-activated by a low magnitude stress field.  相似文献   

The active fault system of SW Alps     

Guillaume Sanchez  Yann Rolland  Dimitri Schreiber  Gérard Giannerini  Michel Corsini  Jean-Marc Lardeaux 《Journal of Geodynamics》2010,49(5):296-302

Historical and active seismicity in the south-western Alps (France and Italy) shows the recurrence of relatively high-magnitude earthquakes (M ≥ 5.8), like the one that recently affected the Italian Apennine range (M = 6.3 on the 30th March 2009). However, up-to-date detailed mapping of the active fault network has been poorly established. The evaluation of seismological hazard in particular in the highly populated French and Italian coastal region cannot be done without this. Here, we present a detailed study of the main active fault system, based on geological observations along the south-western flank of the Alpine arc. This N140° right-lateral strike-slip active fault system runs along the edge of the Argentera-Mercantour range and can be followed down to the Mediterranean Sea. It is evidenced by (1) Holocene offsets of glacial geomorphology witnessing ongoing fault activity since 10 ka, (2) widespread recent (10–20 Ma) pseudotachylytes featuring long term activity of the faults, (3) active landslides along the main fault zone, (4) geothermal anomalies (hot springs) emerging in the active faults, (5) ongoing low-magnitude seismic activity and (6) localization of the main historical events. In the light of our investigations, we propose a new tectonic pattern for the active fault system in the south-western Alps.  相似文献   

Holocene hydrological changes in south-western Mediterranean as recorded by lake-level fluctuations at Lago Preola,a coastal lake in southern Sicily,Italy     

Michel Magny  Boris Vannière  Camilla Calo  Laurent Millet  Aurélie Leroux  Odile Peyron  Gianni Zanchetta  Tommaso La Mantia  Willy Tinner 《Quaternary Science Reviews》2011,30(19-20):2459-2475

This paper presents a high-resolution lake-level record for the Holocene at Lago Preola (Sicily, southern Italy) based on a specific sedimentological approach, with a chronology derived from AMS radiocarbon dates. It gives evidence of three major successive palaeohydrological periods, with (1) a pronounced dryness during the early Holocene until ca 10300 cal BP, (2) a highstand from ca 10300 to 4500 cal BP, and (3) a marked lowstand from 4500 cal BP to present. Large amplitude lake-level fluctuations characterise two transition phases at ca 10300–9000 and 6400–4500 cal BP. Period 2 was interrupted between 8300 and 7000 cal BP by a dry phase that was punctuated to ca 7300 cal BP by the deposition of a tephra from neighbouring Pantelleria Island. Comparisons of the Preola record with other palaeohydrological records along north–south and west–east transects in the Mediterranean show contrasting patterns of hydrological changes: north (south) of around 40°N latitude, the records highlight a mid-Holocene period characterised by lake-level minima (maxima). Humid mid-Holocene conditions over the Mediterranean south of 40°N were probably linked to a strong weakening of the Hadley cell circulation and of monsoon winds. We suggest that the maximum of humidity in the Mediterranean during the mid-Holocene was characterised by humid winters to the north of 40°N and humid summers to the south. On a multi-centennial scale, the high-resolution palaeohydrological reconstructions in the central Mediterranean area reveal a strong climate reversal around 4500–4000 cal BP, with contrasting changes in the hydrological cycle. In addition to seasonal and inter-hemispherical changes related to orbital forcing, this major oscillation might be related to non-linear responses of the climatic system to the gradual decrease in summer insolation at northern latitudes. Another major climate oscillation around 7500–7000 cal BP may have resulted from the combined effects of (1) a strong rate of change in insolation, and (2) variations in solar activity. Finally, comparisons of the Preola lake-level record with Sicilian pollen records suggest a strong influence of moisture availability on vegetation development in Sicily. Very dry early Holocene conditions probably prevented the expansion of coastal evergreen forests, while decreasing moisture availability since the onset of the late Holocene may have exacerbated effects of intensive land-use.  相似文献   

Sea ice variations in the central Canadian Arctic Archipelago during the Holocene     

Lindsay L. Vare  Guillaume Massé  Thomas R. Gregory  Christopher W. Smart  Simon T. Belt 《Quaternary Science Reviews》2009,28(13-14):1354-1366

A sea ice record for Barrow Strait in the Canadian Arctic Archipelago (CAA) is presented for the interval 10.0–0.4 cal. kyr BP. This Holocene record is based primarily on the occurrence of a sea ice biomarker chemical, IP₂₅, isolated from a marine sediment core obtained from Barrow Strait in 2005. A core chronology is based on ¹⁴C AMS dating of mollusc shells obtained from ten horizons within the core. The primary IP₂₅ data are compared with complementary proxy data obtained from analysis of other organic biomarkers, stable isotope composition of bulk organic matter, benthic foraminifera, particle size distributions and ratios of inorganic elements. The combined proxy data show that the palaeo-sea ice record can be grouped according to four intervals, and these can be contextualised further with respect to the Holocene Thermal Maximum (HTM). Spring sea ice occurrence was lowest during the early–mid Holocene (10.0–6.0 cal. kyr BP) and this was followed by a second phase (6.0–4.0 cal. kyr BP) where spring sea ice occurrence showed a small increase. Between 4.0 and 3.0 cal. kyr BP, spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the HTM. Elevated spring sea ice occurrences continued from 3.0 to 0.4 cal. kyr BP, although they were more variable on shorter timescales. Within this fourth interval, we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the Mediaeval Warm Period and the Little Ice Age respectively. Comparisons are made between our proxy data with those obtained from other palaeo-climate and sea ice studies for the CAA.  相似文献