Abstract Cavernous weathering (tafoni) is described from coarse-grained granitic bedrock in North... more Abstract Cavernous weathering (tafoni) is described from coarse-grained granitic bedrock in Northern Victoria Land (Antarctica), northern Sardinia (Italy) and southwestern Australia. It also occurs elsewhere in the world and on other coarse-grained lithologies. The cause of this unusual in-situ flaking and granular disintegration is problematic. Azonal conditions appear to be: (1) the presence of salt, (2) aridity and (3) high evaporation and sublimation rates. Zonal (site-specific) considerations are: (1) snow may transport salts far inland in Antarctica and (2) epilithic and endolithic lichen growth may assist biological weathering in Sardinia and Antarctica. In stable landscapes of great antiquity, such as southwestern Australia, tafoni-like forms appear to have developed over millions of years; they suggest that salts in solution move slowly and continuously towards the surface where they evaporate. Combinations of these conditions result in tafoni in these different environments.
Netherlands Journal of Geosciences - Geologie en Mijnbouw, 2012
The Late Pleistocene surface paleohydrography of the New Jersey Pine Barrens consisted of a serie... more The Late Pleistocene surface paleohydrography of the New Jersey Pine Barrens consisted of a series of broad braided alluvial surfaces with meandering paleochannels. This drainage is best explained in terms of impermeable (i.e. frozen) substrate, high sediment load, variable or decreasing discharge, and eolian sedimentary dynamics. Evidence for eolian activity is provided by wind-abraded sand grains, coversand, dunes, ventifacts, deflation hollows and wind-polished boulders. In several places stream avulsion occurred due to channel infilling by locally-derived wind-blown sediment. The braided and meandering river systems that characterise the tundra and polar semi-desert lowlands of the Western Canadian Arctic are described as modern analogs.
Tundra and polar desert environments characterize the islands of the Western Canadian Arctic. Pri... more Tundra and polar desert environments characterize the islands of the Western Canadian Arctic. Prince Patrick Island is a typical polar semi-desert; Banks Island illustrates the intermixing of polar-desert and tundra environments. Interpretation of these periglacial landscapes must consider not only the normal links that exist between rocks, relief, climate and weathering but also specific relationships between low temperature, aridity, snow, frozen ground, wind and vegetation.
Rock varnish, erosional grooves, and well-developed cavernous weathering phenomena occur in close... more Rock varnish, erosional grooves, and well-developed cavernous weathering phenomena occur in close association on a small biotite-monzogranite nunatak in the Northern Foothills region, Northern Victoria Land, Antarctica. The grooves, similar in appearance to the 'rinnenkarren' described in the karst literature, are developed on steeply inclined (>35°) bedrock surfaces while the rock varnish occurs on adjacent, more gently sloping (<15°) bedrock surfaces. The varnish forms a resistant carapace through which small weathering pits have developed and below which are large cavernously weathered hollows (taffoni). We argue that the intimate association between the grooves and the rock varnish indicate the nunatak has been exposed to a long period of subaerial weathering. The preservation of both phenomena supports (a) the idea that landscape modification in this exceptionally cold and arid region of Antarctica is very slow and (b) the long-term stability of the Antarctic ice sheet.
The 'frost-thaw' or thermokarst-lake-basin hypothesis, first invoked by P. E. Wolfe in 1953 to ex... more The 'frost-thaw' or thermokarst-lake-basin hypothesis, first invoked by P. E. Wolfe in 1953 to explain the enclosed depressions and shallow basins ('spungs') of southern New Jersey, is reexamined. The most probable explanation is that they formed in late Wisconsinan times as deflation hollows, or 'blowouts', when strong katabatic winds flowed southwards from the continental ice margin across the sparsely vegetated, tundra terrain of the Pine Barrens. Wedge structures and cryoturbation phenomena suggest the existence of either permafrost or deep seasonal frost, and imply mean annual air temperatures of between 0.5°C and 6°C. When the groundwater table rose in late-glacial times, the hollows became ponds or wetlands. These were utilized as early as 12,000 years ago by palaeoindian and early archaic cultures as hunting camp sites. Today, many of these wetlands are drying up as the regional water table falls in response to increased water usage from agriculture and urbanization. Copyright 2001 John Wiley & Sons, Ltd. RÉSUMÉ L'hypothèse gel-dégel ou de bassins thermokarstiques, invoquée pour la première fois par P.E. Wolfe en 1953 pour expliquer les dépressions fermées et les bassins peu profonds (spungs) du sud du New Jersey, est réexaminée. L'explication la plus probable est que ces dépressions se sont forméesà la fin du Wisconsin comme des creux de déflation au moment où des vents catabatiques violents soufflaient vers le sud sur la marge de la calotte glaciaire et sur la végétationéparse de la toundra qui couvrait les Pine Barrens. Des structures en coin et des cryoturbations suggèrent l'existence, soit d'un pergélisol, soit d'un gel profond saisonnier, et impliquent des températures annuelles de l'air comprises entre-0.5 et-6°C. Quand la nappe aquifère s'estélevéeà la fin de la glaciation, les dépressions sont devenues des mares ou des zones humides. Elles furent utilisées comme sites de camps de chasse, il y a 12000 ans par des Paléoindiens et des cultures archaïques primitives. Aujourd'hui, beaucoup de ces terres humides disparaissentà la suite de l'abaissement régional de la nappe aquifère résultant d'un accroissement de l'utilisation d'eau par l'agriculture et l'urbanisation.
Norsk Geografisk Tidsskrift - Norwegian Journal of Geography, 2006
Hanne H. Christiansen, The University Centre in Svalbard, UNIS, Geology Department, P.O. Box 156,... more Hanne H. Christiansen, The University Centre in Svalbard, UNIS, Geology Department, P.O. Box 156, NO-9171 Longyearbyen, Svalbard, Norway. E-mail: [email protected]; Hugh M. French, Departments of Earth Sciences and Geography, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. E-mail: [email protected]; Ole Humlum, Department of Physical Geography, Institute of Geosciences, University of Oslo, Box 1042 Blindern, NO-0316 Oslo; The University Centre in Svalbard, UNIS, P.0. Box 156, 9171 Longyearbyen, Norway. E-mail: [email protected]
Cryostratigraphy adopts concepts from both Russian geocryology and modern sedimentology. Structur... more Cryostratigraphy adopts concepts from both Russian geocryology and modern sedimentology. Structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures. Typically, layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost. 'Cryofacies' can be defined according to patterns of sediment characterized by distinct ice lenses and layers, volumetric ice content and ice-crystal size. Cryofacies can be subdivided according to cryostructure. Where a number of cryofacies form a distinctive cryostratigraphic unit, these are termed a 'cryofacies assemblage'. The recognition, if present, of (i) thaw unconformities, (ii) other ice bodies such as vein ice (ice wedges), aggradational ice and thermokarst-cave ('pool') ice, and (iii) ice, sand and gravelly pseudomorphs is also important in determining the nature of the freezing process, the conditions under which frozen sediment accumulates, and the history of permafrost.
ABSTRACT This paper accompanies a map that shows the extent of permafrost in the Northern Hemisph... more ABSTRACT This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice-wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo-temperatures that are inferred on the basis of present-day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately &amp;lt;1000 m a.s.l.). Striking features that appear from the map are (i) the narrow permafrost zone in North America, which contrasts with the broader LPM permafrost zone in Eurasia (that may be related to different snow thickness or vegetation cover), (ii) the zonal extent of former LPM permafrost (that may reflect sea-ice distribution), which contrasts with the present-day pattern of permafrost extent (especially in Eurasia) and (iii) the relatively narrow zones of LPM discontinuous permafrost (that may indicate strong temperature gradients).
Abstract Cavernous weathering (tafoni) is described from coarse-grained granitic bedrock in North... more Abstract Cavernous weathering (tafoni) is described from coarse-grained granitic bedrock in Northern Victoria Land (Antarctica), northern Sardinia (Italy) and southwestern Australia. It also occurs elsewhere in the world and on other coarse-grained lithologies. The cause of this unusual in-situ flaking and granular disintegration is problematic. Azonal conditions appear to be: (1) the presence of salt, (2) aridity and (3) high evaporation and sublimation rates. Zonal (site-specific) considerations are: (1) snow may transport salts far inland in Antarctica and (2) epilithic and endolithic lichen growth may assist biological weathering in Sardinia and Antarctica. In stable landscapes of great antiquity, such as southwestern Australia, tafoni-like forms appear to have developed over millions of years; they suggest that salts in solution move slowly and continuously towards the surface where they evaporate. Combinations of these conditions result in tafoni in these different environments.
Netherlands Journal of Geosciences - Geologie en Mijnbouw, 2012
The Late Pleistocene surface paleohydrography of the New Jersey Pine Barrens consisted of a serie... more The Late Pleistocene surface paleohydrography of the New Jersey Pine Barrens consisted of a series of broad braided alluvial surfaces with meandering paleochannels. This drainage is best explained in terms of impermeable (i.e. frozen) substrate, high sediment load, variable or decreasing discharge, and eolian sedimentary dynamics. Evidence for eolian activity is provided by wind-abraded sand grains, coversand, dunes, ventifacts, deflation hollows and wind-polished boulders. In several places stream avulsion occurred due to channel infilling by locally-derived wind-blown sediment. The braided and meandering river systems that characterise the tundra and polar semi-desert lowlands of the Western Canadian Arctic are described as modern analogs.
Tundra and polar desert environments characterize the islands of the Western Canadian Arctic. Pri... more Tundra and polar desert environments characterize the islands of the Western Canadian Arctic. Prince Patrick Island is a typical polar semi-desert; Banks Island illustrates the intermixing of polar-desert and tundra environments. Interpretation of these periglacial landscapes must consider not only the normal links that exist between rocks, relief, climate and weathering but also specific relationships between low temperature, aridity, snow, frozen ground, wind and vegetation.
Rock varnish, erosional grooves, and well-developed cavernous weathering phenomena occur in close... more Rock varnish, erosional grooves, and well-developed cavernous weathering phenomena occur in close association on a small biotite-monzogranite nunatak in the Northern Foothills region, Northern Victoria Land, Antarctica. The grooves, similar in appearance to the 'rinnenkarren' described in the karst literature, are developed on steeply inclined (>35°) bedrock surfaces while the rock varnish occurs on adjacent, more gently sloping (<15°) bedrock surfaces. The varnish forms a resistant carapace through which small weathering pits have developed and below which are large cavernously weathered hollows (taffoni). We argue that the intimate association between the grooves and the rock varnish indicate the nunatak has been exposed to a long period of subaerial weathering. The preservation of both phenomena supports (a) the idea that landscape modification in this exceptionally cold and arid region of Antarctica is very slow and (b) the long-term stability of the Antarctic ice sheet.
The 'frost-thaw' or thermokarst-lake-basin hypothesis, first invoked by P. E. Wolfe in 1953 to ex... more The 'frost-thaw' or thermokarst-lake-basin hypothesis, first invoked by P. E. Wolfe in 1953 to explain the enclosed depressions and shallow basins ('spungs') of southern New Jersey, is reexamined. The most probable explanation is that they formed in late Wisconsinan times as deflation hollows, or 'blowouts', when strong katabatic winds flowed southwards from the continental ice margin across the sparsely vegetated, tundra terrain of the Pine Barrens. Wedge structures and cryoturbation phenomena suggest the existence of either permafrost or deep seasonal frost, and imply mean annual air temperatures of between 0.5°C and 6°C. When the groundwater table rose in late-glacial times, the hollows became ponds or wetlands. These were utilized as early as 12,000 years ago by palaeoindian and early archaic cultures as hunting camp sites. Today, many of these wetlands are drying up as the regional water table falls in response to increased water usage from agriculture and urbanization. Copyright 2001 John Wiley & Sons, Ltd. RÉSUMÉ L'hypothèse gel-dégel ou de bassins thermokarstiques, invoquée pour la première fois par P.E. Wolfe en 1953 pour expliquer les dépressions fermées et les bassins peu profonds (spungs) du sud du New Jersey, est réexaminée. L'explication la plus probable est que ces dépressions se sont forméesà la fin du Wisconsin comme des creux de déflation au moment où des vents catabatiques violents soufflaient vers le sud sur la marge de la calotte glaciaire et sur la végétationéparse de la toundra qui couvrait les Pine Barrens. Des structures en coin et des cryoturbations suggèrent l'existence, soit d'un pergélisol, soit d'un gel profond saisonnier, et impliquent des températures annuelles de l'air comprises entre-0.5 et-6°C. Quand la nappe aquifère s'estélevéeà la fin de la glaciation, les dépressions sont devenues des mares ou des zones humides. Elles furent utilisées comme sites de camps de chasse, il y a 12000 ans par des Paléoindiens et des cultures archaïques primitives. Aujourd'hui, beaucoup de ces terres humides disparaissentà la suite de l'abaissement régional de la nappe aquifère résultant d'un accroissement de l'utilisation d'eau par l'agriculture et l'urbanisation.
Norsk Geografisk Tidsskrift - Norwegian Journal of Geography, 2006
Hanne H. Christiansen, The University Centre in Svalbard, UNIS, Geology Department, P.O. Box 156,... more Hanne H. Christiansen, The University Centre in Svalbard, UNIS, Geology Department, P.O. Box 156, NO-9171 Longyearbyen, Svalbard, Norway. E-mail: [email protected]; Hugh M. French, Departments of Earth Sciences and Geography, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. E-mail: [email protected]; Ole Humlum, Department of Physical Geography, Institute of Geosciences, University of Oslo, Box 1042 Blindern, NO-0316 Oslo; The University Centre in Svalbard, UNIS, P.0. Box 156, 9171 Longyearbyen, Norway. E-mail: [email protected]
Cryostratigraphy adopts concepts from both Russian geocryology and modern sedimentology. Structur... more Cryostratigraphy adopts concepts from both Russian geocryology and modern sedimentology. Structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures. Typically, layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost. 'Cryofacies' can be defined according to patterns of sediment characterized by distinct ice lenses and layers, volumetric ice content and ice-crystal size. Cryofacies can be subdivided according to cryostructure. Where a number of cryofacies form a distinctive cryostratigraphic unit, these are termed a 'cryofacies assemblage'. The recognition, if present, of (i) thaw unconformities, (ii) other ice bodies such as vein ice (ice wedges), aggradational ice and thermokarst-cave ('pool') ice, and (iii) ice, sand and gravelly pseudomorphs is also important in determining the nature of the freezing process, the conditions under which frozen sediment accumulates, and the history of permafrost.
ABSTRACT This paper accompanies a map that shows the extent of permafrost in the Northern Hemisph... more ABSTRACT This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice-wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo-temperatures that are inferred on the basis of present-day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately &amp;lt;1000 m a.s.l.). Striking features that appear from the map are (i) the narrow permafrost zone in North America, which contrasts with the broader LPM permafrost zone in Eurasia (that may be related to different snow thickness or vegetation cover), (ii) the zonal extent of former LPM permafrost (that may reflect sea-ice distribution), which contrasts with the present-day pattern of permafrost extent (especially in Eurasia) and (iii) the relatively narrow zones of LPM discontinuous permafrost (that may indicate strong temperature gradients).
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