Glacial Geology of the Tonasket – Spectacle Lake Area, Okanogan County, Washington
Glacial sediments exposed in the northern Okanogan trough consist of Fraser advance stratified drift, lodgement till, and recessional stratified drift. No older Quaternary sediments were recognized in the mapped area. The advance stratified drift unit is composed of upward-coarsening braided-stream...
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| Format: | Text |
| Language: | English |
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Western CEDAR
1985
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| Online Access: | https://cedar.wwu.edu/wwuet/836 https://cedar.wwu.edu/cgi/viewcontent.cgi?article=1858&context=wwuet |
| Summary: | Glacial sediments exposed in the northern Okanogan trough consist of Fraser advance stratified drift, lodgement till, and recessional stratified drift. No older Quaternary sediments were recognized in the mapped area. The advance stratified drift unit is composed of upward-coarsening braided-stream outwash with locally intercalated lacustrine and alluvial fan sediments. An upsection change in facies within the unit suggests a gradation from distal to proximal deposition of proglacial outwash with time in Spectacle Lake Coulee. The gradation probably records the approach of Cordilleran ice into the area during the Fraser advance. Upland regions of the study area are mantled by a lodgement till complex that typically exhibits a streamlined and sometimes drumlinoid surface morphology. Interbeds of glaciolacustrine and glaciofluvial sediment containing dropstones and inclusions of diamicton are common. Thick sections of lodgement till overlying the interbeds indicate that they were deposited in subglacial lakes and streams beneath active ice of the Okanogan lobe. Crudely stratified till subunits of differing color and texture are present at some outcrops in the central portion of the study area. These subunits may have been deposited through a process of superimposed till lodgement beneath multiple, competing ice streams of a composite Okanogan lobe. The Okanogan Valley and coulees tributary to it contain voluminous fills of recessional stratified drift. Kame terraces at higher elevations are predominantly erosional in origin and probably signify relatively rapid lowering of the ice-sheet surface during their formation. Kame terraces comprised of ice-contact glaciolacustrine and glaciofluvial sediment are more common at lower elevations and record sedimentation in a series of local ice-marginal lakes and streams. The most prominent set of kame terraces occurs along the Okanogan Valley and is collectively known as the "Great Terrace". In the study area, the "Great Terrace" is composed of highly deformed ice-contact ... |
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