Les terrasses de cryoplanation dans le nord du Yukon : distribution, genèse et âge

Abstract

Les terrasses de cryoplanation sont une forme fréquente et caractéristique dans le nord du Yukon. Plus de 1000 ont été identifiées dans les dolomies, les calcaires, les argilites et les quartzites de cette région. Situées sur des versants, elles dominent toujours des pediments. Elles ne sont jamais présentes sur des versants façonnés par l'érosion fluviale. Lagélifraction, lagélifluxion et le ruissellement aréolaire associés à l'existence de plaques de neige résiduelles paraissent être les processus les plus aptes à les façonner. À côté de ces processus, la dissolution des roches carbonatées joue un rôle secondaire. Plusieurs terrasses semblent avoir une origine structurale, d'autres seraient des fragments de pediments. Les repères chronologiques ne sont pas nombreux pour reconstituer les étapes de la morphogénèse du paysage dans lequel s'est inscrite la mise en place des terrasses. Néanmoins, au sud des monts Keele, la datation de concrétions prélevées dans les cavernes permet d'avancer l'hypothèse que quelques terrasses pourraient être pré-sangamoniennes et peut-être plus vieilles que 1,2 Ma. Les terrasses sont actuellement inactives à l'exception de quelques-unes situées dans les monts Richardson.More than 1000 cryoplanation terraces were identified in the higher mountains of the northern Yukon. Distribution of these landforms is strongly influenced by substrate geology. They occur only in dolomite, limestone, argillite and quartzite rocks. They are situated on slopes facing pediments, never on slopes of ravines. About 50% occur between 700-900 m of elevation, and nearly 40% are situated on northeast to southwest facing slopes. Gelifluction, slopewash, eluviation and frost shattering associated with snowpatches are the processes involved in enlarging the terraces. The dissolution of carbonate in limestone rocks can also be a process responsible for the shaping of terraces. Some terraces are structuraly controled, and others seem to be the remains of pediments. The age of the terraces is not well known but dating of speleothems from the Keele Range gives evidence that some terraces postdate the Sangamonian. Nearly all the visited terraces appear presently inactive, except in the Richardson Mountains.Die Kryoplanationsterrassen sind eine im Norden von Yukon hâufig auftretende und charakteristische Form. Mehr als 1000 sind in den Dolomit-, Kalk-, Ton- und Quarz-Felsen dieses Gebiets identifiziert worden. Sie befinden sich an Abhàngen und beherrschen immer die Pedimente. Man findet sie niemals an durch Fluss-Erosion geformten Abhàngen. Frostsprengung, Frostfliessen und Regenspùlung scheinen sie gemeinsam mit restlichen Schneeflâchen am wirksamsten geformt zuhaben. Neben diesen Prozessen spielt die Auflôsung der Karbonat-Felsen eine zweitrangige Rolle. Einige Terrassen scheinen strukturbedingten Ursprungs zu sein, andere Fragmente von Pedimenten. Um die Etappen der Morphogenese der Landschaft, in der sich die Terrassen gebildet haben, zu rekonstuieren, gibt es nicht viele chronologische Anhaltspunkte. Im Suden der ...

Age and development of active cryoplanation terraces in the alpine permafrost zone at Svartkampan, Jotunheimen, southern Norway

“…Vague generalisations have resulted from relative-age dating based on morphostratigraphy, weathering-rind thickness, vegetation, or lichen cover (Péwé, 1970; Reger, 1975; Lauriol et al, 1997; Nelson, 1998). However, it has been concluded that they probably develop over very long periods of time, which supports similar ideas based on the observation that they are well developed in terrain that has never been glaciated or was not glaciated during the last glaciation (Reger and Péwé, 1976; Lauriol and Godbout, 1988; Nelson and Nyland, 2017). To the authors’ knowledge, the results of numerical-age dating techniques have been presented in two published papers only (Cremeens et al, 2005; Lauriol et al, 2006): the first applied 36 Cl cosmogenic-nuclide exposure-age dating to two possible cryoplanation summit flats; the second obtained nine 14 C dates from the regolith cover of the treads of undoubted cryoplanation terraces.…”

“…However, although cryoplanation terraces have been widely recognised in regions with present or former nonglacial cold climates, such as Siberia (Boch and Krasnov, 1994; Demek, 1968; Czudek, 1995), Mongolia (Richter et al, 1963), Alaska (Reger and Péwé, 1976; Nelson, 1998; Nelson and Nyland, 2017), northern Canada (Lauriol and Godbout, 1988; Lauriol et al, 2006), Central Europe (Demek, 1969b; Traczyk and Migon, 2000; Křížek, 2007), Iceland (Schunke and Heckendorff, 1976; Schunke, 1977), the Andes (Grosso and Corte, 1991), Antarctica (Hall, 1997; Hall and André, 2010), and the British Isles (Te Punga, 1956; Waters, 1962), criteria for the recognition of active features are largely lacking. In the absence of dating evidence, moreover, most examples discussed in the literature are of unknown age, and many are regarded as relict.…”

Do Periglacial Landscapes Exist? A Discussion of the Upland Landscapes of Northern Interior Yukon, Canada

“…These flat surfaces are developed in highly resistant argillites and chert of the Precambrian Neruokpuk Formation. Similar bedrock benches are described from elsewhere in Yukon (Hughes, 1990;Rampton, 1982;Lauriol and Godbout, 1988). Their problem of interpretation is compounded by the fact that quantitative field studies have yet to demonstrate the active formation of these terraces.…”

“…Similar bedrock benches are described from elsewhere in Yukon (Hughes, ; Rampton, ; Lauriol and Godbout, ). Their problem of interpretation is compounded by the fact that quantitative field studies have yet to demonstrate the active formation of these terraces.…”

A characteristic periglacial landform: Automated recognition and delineation of cryoplanation terraces in eastern Beringia

“…CTs are prominent landforms throughout unglaciated portions of interior and western Alaska, 15,16 Yukon Territory, 17,18 and the Russian Far East, particularly Chukotka 19,20 . However, many unresolved questions about their genesis and developmental history remain 19,20 .…”