Present at Site A and Site C of Chester Bluff. The CB tephra, the upper-most bed at Site A, includes sections of exceptionally preserved primary bedding. CB comprises four individual beds of ash divided by thin laminae of silt, likely representing several eruptions from the same source that occurred over a period of days to weeks to possibly years. The lowermost layer of tephra is pink; less than or equal to 1 cm thick and separated from the overlying beds by less than or equal to 2 cm of silt, and is referred to here as CB2. The next two beds are locally Fe-stained but have a distinct salt and pepper appearance and are up to 2.5 cm thick. The upper-most bed is the thickest, up to 5 cm, also has a salt and pepper appearance, but displays winnowing, with heavier phenocrysts concentrated near the base of the bed. These three beds are collectively termed CB1. At Site C, CB is up to 5 cm thick and generally appears as a single bed, although the lower pink bed is locally visible. At Site C, there are two tephra beds directly above CB, the Coal Creek (CC) and Charley Village (CV) tephra. All three beds are faulted steeply toward the downstream end of the bluff. Generally CB2 is distinguishable from CB1 by a higher percentage of thick-walled pumice that is rich in microcrysts and a lower percentage of phenocrysts. CB2 is richer in ortho-pyroxenes and has a distinct population of red amphibole.
An extensive middle to late Pleistocene tephrochronologic record from east-central Alaska
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