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Waythomas, C.F., 1990

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Bibliographic Reference

Waythomas, C.F., 1990, Quaternary geology and late-Quaternary environments of the Holitna lowland, and Chuilnuk-Kiokluk Mountains region, interior southwestern Alaska: University of Colorado, Boulder, Ph.D. dissertation, 271 p., illust., maps.

Abstract

Surficial deposits and stratigraphic sequences in the Holitna lowland and Chuilnuk/Kiokluk Mountains area of interior southwestern Alaska provide evidence of Quaternary environmental change. Surficial geologic mapping in the Chuilnuk and Kiokluk Mountains has revealed a sequence of glacial deposits representing alpine valley glaciation of the area. Three major glacial episodes and one minor glacial advance have been recognized. The Oskawalik Creek glacial interval represents the oldest and most extensive glaciation of the area, and consists of highly subdued morainal remnants and widely dispersed erratic boulders that are confined mainly to drainage interfluves. The Chuilnuk glacial interval is named for a sequence of moraines, outwash deposits and ice-marginal drainage features that are less extensive and more fresh appearing than Oskawalik Creek age deposits. The Buckstock glacial interval is named for fresh-appearing, hummocky drift, with well-defined lateral and terminal moraines that are less extensive than drift of the Chuilnuk glaciation. The Kiokluk Peak advance represents limited cirque glaciation during late (?) Holocene time. Glacier reconstructions indicate that ELAs were lowered by about 300 m during the last (Buckstock) glaciation and 350-450 m during the penultimate (Chuilnuk) glaciation, and suggest late-Pleistocene temperature depressions of 2-3oC from modern values. Stratigraphic sequences in the Holitna lowland reveal a complex assemblage of eolian, fluvial and tephra-bearing organic deposits. Lithostratigraphic relations in the lowland permit the definition of regional stratigraphic units, and correlation with similar sequences in coastal southwest and interior Alaska. The Kulukbuk Formation is named for distal glacifluvial sand, sub-horizontally bedded sand sheets and loess that contains the ca. 150 ka Old Crow tephra. The Holitna Complex comprises organic silt, peat and reworked tephra, that formed under mesic interstadial-like conditions, and is correlated with the Boutellier interval of Hopkins (1982). The Beaverhouse Formation is named for non-organic, sand-sheet deposits and loess that formed during the last (ca. 12-25 ka) glacial interval.

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