GEOSCAN Search Results: Fastlink


TitleTerrain inventory and Quaternary history of the Pelly River area, Yukon Territory
AuthorJackson, L E, Jr
SourceGeological Survey of Canada, Memoir 437, 1994, 47 pages (17 sheets),
PublisherNatural Resources Canada
MapsPublication contains 17 maps
Map Info.surficial geology, lithological, landforms, 1:100,000
Map Info.surficial geology, ice flow directions, 1:500,000
Mediapaper; on-line; digital
RelatedThis publication contains the following publications
File formatpdf
NTS105F; 105G; 105J; 105K; 105H; 105I
AreaMacmillan Highland; Pelly Mountains; Ross Lowland; Pelly River
Lat/Long WENS-134.0000 -128.0000 63.0000 61.0000
Subjectssurficial geology/geomorphology; geochemistry; terrain inventories; glaciation; deglaciation; ice sheets; glacial stages; tills; glaciofluvial deposits; colluvial deposits; glaciolacustrine deposits; glacial deposits; till geochemistry; landforms; fluvial deposits; organic deposits; alluvial deposits; glacial history; ice movement directions; Holocene; drift deposits; lithology; debris flows; Cordilleran Ice Sheet; McConnell Glacial Stage; McConnell Till; Quaternary
Illustrationssketch maps; photographs; analyses; stratigraphic columns
Released1994 05 01; 2015 09 03
AbstractThe study area, encompassing large tracts of land around the headwaters of Pelly, Liard, and Nisutlin rivers, was covered by the Cordilleran Ice Sheet during the (last) McConnell Glaciation between 26.5 and 10 ka. At its acme, the ice sheet in this area was a complex of anastomosed valley glaciers comprising four sectors, each flowing from mountainous source areas and separated by mountains or ice divides. Underlying topography always directed ice flow. The ice sheet disappeared by stagnation and downwasting with the uplands first to be ice free and major valleys last. Deposits of an older glaciation or an early stade of McConnell Glaciation are restricted to Tintina Trench. Till is the most widespread glacial deposit, usually in blankets and veneers over bedrock. Tills have a low clay content and plasticity and a variable carbonate content. Till geochemistry shows the greatest diversity between tills derived from ophiolite and sedimentary suites. Glaciofluvial deposits, predominantly gravels, are common in most valleys as kame, esker, and planar deposits. Glaciolacustrine silts and clays occur where glacial ice impeded drainage during deglaciation. These deposits commonly contain massive ground ice and, consequently, are subject to retrogressive thaw sliding. Colluvial deposits and their landforms form the largest nonglacial category in the study area. Because they are formed by a continuous spectra of chiefly nonfluvial processes, they intergrade. For example, a continuous series of landforms exists among talus cones, rock glaciers, and colluvial fans and between felsenmeer and solifluction deposits. Five large rock avalanches or sturzstoms (>106 m3) have occurred in Pelly Mountains in postglacial time.However, smaller scale rockfalls (<106 m3) are volumetrically the most significant and widespread form of rapid slope failure. Fluvial deposits, predominantly gravels, form fans, floodplains, and terraces. Some floodplains contain significant fine lacustrine and overbank sediments - primarily silts and clays; these may contain clear ice lenses and develop thermokarst. Much material of the alluvial fans and terraced gravels was deposited during early postglacial time when rates of sediment transport were conditioned by glaciation rather than by the present erosional regime. Organic deposits are present in floodplains, in paludifying lakes, and as blanket bog. These deposits usually contain clear ice lenses that are subject to growth, heave, and collapse; they are particularly sensitive to disturbance.