Sample: Jensen_2008_Chester_Bluff_Preido_Hill_tephra
| Sample ID: |
Jensen_2008_Chester_Bluff_Preido_Hill_tephra [1] [2] |
| Station ID: |
Jensen_2008_Chester_Bluff |
| AT Num: |
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| Volcano: |
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| Possible source: |
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| Eruption: |
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| Collector: |
Jensen, B. J. L. |
| Date sampled: |
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| Sample type 1: |
Tephra Fall |
| Color: |
white-yellow |
| Final unit: |
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| Text Description: |
Present at all three sites of Chester Bluff, Site A, Site B, and Site C. The Preido Hill (PrH) tephra is reworked with MacGregor Cabin (MC) tephra at Site A1. PrH/MC and SR are heavily faulted, reworked and dipping steeply at both Site A and A1. Loess associated with the reworked PrH/MC is strongly mottled, Fe-stained, andincludes small organic horizons that are reworked and overturned. Solifluction may have caused the mottling and overturning of the tephra beds or, alternatively, a faulted block of silt may have obscured the true stratigraphic position of the tephra beds. At Site B, Tom King (TK), MC, PrH, Ben Creek (BC) and Yukon Tanana (YT) are found within 2m of one another. SR, TK, MC and PrH are deposited within greyish brown loess 0.5 to 1m below a major organic unit that contains BC and YT. At the downstream end of the 6m lateral section the tephra beds are reworked and faulted downward. At the upstream end, the major organic unit above SR, TK, MC and PrH is deformed along its base, causing the tephra beds to be overturned and partially reworked into the base of the unit. A 6m wide trench was excavated to fully delineate the tephrostratigraphic relations of the six tephra beds. PrH is a continuous white-yellow bed up to 4 cm thick with sharp contacts. PrH and MC are very similar geochemically and are distinguished largely by stratigraphy in this relatively undisturbed exposure where they both form distinct, laterally continuous beds consistently separated by 2 cm of silt. At Site C, the reworked PrH/MC and TK are found as an isolated pod. PrH/MC are strongly deformed and down-faulted vertically over 3m toward the downstream side of this exposure. Low percentage of phenocrysts (<20%) and contain a population of distinctively thick-walled pumice and glass shards. The composition reported was calculated from analyses of one sample: UA1217. |
| Sample Location: |
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References Cited
Jensen, B.J.L., Froese, D.L., Preece, S.J., Westgate, J.A., and Stachel, Thomas, 2008, An extensive middle to late Pleistocene tephrochronologic record from east-central Alaska: Quaternary Science Reviews, v. 27, p. 411-427, doi:10.1016/j.quascirev.2007.10.010 .
Jensen, B.J.L., 2007, Tephrochronology of Middle to Late Pleistocene Loess in Eastcentral Alaska: University of Alberta M.S. thesis, 120 p.