GEOSCAN, résultats de la recherche


TitreSeafloor mud volcanoes: evidence of a dynamic Beaufort continental shelf
AuteurBlasco, S M; Shearer, J M; Blasco, K A; Bennett, R
Source38th international Arctic workshop 2008, program and abstracts; par Institute of Arctic and Alpine Research; 2008 p. 31-32
Séries alt.Secteur des sciences de la Terre, Contribution externe 20070586
Réunion38th International Arctic Workshop 2008; Boulder; US; mars 5-7, 2008
ProvinceRégion extracotière du nord
Lat/Long OENS-141.0000 -128.0000 72.0000 68.7500
Sujetsvolcans de boue; levés géophysiques; levés sismiques; levés de reflexion sismiques; sonar latéral; topographie du fond océanique; topographie du fond océanique; coulées de débris; dépôts de coulée de débris; elements glaciaires; pingos; dépôts glaciaires; géologie marine; géophysique; géologie des dépôts meubles/géomorphologie
Illustrationssketch maps; images
Résumé(disponible en anglais seulement)
Since 1969, over 350 conical shaped mounds have been mapped on the Canadian Beaufort Shelf using multibeam sonar, echo sounder, sidescan sonar, subbottom and shallow seismic reflection profilers. Because these conical mounds are morphologically similar to the 1450 pingos mapped on the adjacent Tuktoyaktuk Peninsula, the seabed features are collectively referred to as pingo-like features (PLFs). PLFs are frequently larger or even elongated in shape in comparison to their terrestrial counterparts.
Seabed PLFs range from 30m to over 1000m in diameter, are 2m to 50m in height, and occur in water depths of 15m to 150m across the shelf. On the eastern and western edges of the Mackenzie Trough PLFs are located along narrow corridors while on the Yukon, central and eastern shelf the features occur as individuals or as clusters of events within a large bathymetric depression. Several PLFs have been impacted by ice keels while others are superimposed on ice scours.
3-Dimensional multibeam sonar images of several of these features reveal the detailed morphology to consist of mud slumps and debris flows. Three features are actively venting gas which is composed of 99 percent methane. These characteristics, along with the linear and clustered nature of their occurrence suggest that some PLFs are mud volcanoes. The well defined mud slumps, lack of recent sedimentation, lack of disturbance by ice keels, venting gas and observed growth on the crest of one feature indicate that some features are active today. The origin of the mud volcanoes is not clear, but they are likely generated by the upward flow of gas and mud from depth. Isotopic analyses of recovered methane indicate a shallow biogenic origin for the gas but stratigraphic evidence suggests gas migration from much greater depths. Some PLFs do display properties similar to terrestrial pingos; such as, surrounding moats and ‘lake-basin’-shaped underlying seismic reflectors, suggesting they may be true pingos.
The eastern edge of the Mackenzie Trough is defined by a linear array of 163 PLFs and at least 10 PLFs delineate the western edge. The trough was excavated by glacial ice streams and then infilled with sediment discharged from the Mackenzie River. The trough is well defined by a U-shaped basal erosional unconformity and infilled with more than 300m of sediment. Gas and fluids may be seeping up from depth, migrating along the base and flanks of the trough unconformity, and escaping to the seabed to generate mud volcanoes.
East of the Mackenzie Trough, the central and eastern Beaufort Shelf is underlain by thick, multilayered, impermeable ice-bearing sediments up to 700m thick. The permafrost layer is disrupted by taliks which may be shallow or pass through the thick permafrost. Gas and fluids migrating from depth would be trapped under or within the permafrost and over time the gas could migrate laterally up-dip and escape through the taliks. The focusing effect of through-going taliks may explain the significant numbers of mud volcanoes found in localized clusters on the central and eastern shelf.
Mud volcanoes are of current research interest as they may indicate the presence of hydrocarbons at depth, may pose threats to navigation, may contribute to greenhouse gas emissions and may be associated with ecologically and biologically significant areas.