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SAMPLE INFO : Jensen_2008_Chester_Bluff_Yukon_Tanana_tephra-P1
Sample ID:Jensen_2008_Chester_Bluff_Yukon_Tanana_tephra-P1
Station ID:Jensen_2008_Chester_Bluff
Latitude:65.38
Longitude:-142.66997
Datum:NAD83
Sample Type 1:Tephra Fall
 Text Description:
Only present at Site B of Chester Bluff. 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. A single isolated white pod of the YT tephra, 1.5 cm thick and 3 cm long, was found 20 cm above BC in a thick fibrous organic bed. Appears to have a low percentage of phenocrysts. Its glass morphology is predominantly chunky glass shards and pumice, with rare frothy pumice. Glass is commonly brown and rich in microcrysts. Phenocrysts are dominated by ortho-pyroxene, green amphibole is present but rare. The composition reported was calculated from analyses of one sample: UA1232.

References:
An extensive middle to late Pleistocene tephrochronologic record from east-central Alaska
Tephrochronology of middle to late Pleistocene loess in east-central Alaska

GEOCHEM DATA
StationIDLatitudeLongitudeGeologistDateVisitedAge InfoVolcanoEruptionLocation DescriptionText DescriptionSample IDSample Type 1Sample Type 2Final UnitMaterialCoeffSiO2TiO2Al2O3FeOTMnOMgOCaONa2OK2OP2O5Total-majorsREF majorsMETH majorsFe2O3/Fe203T origFeO/FeOT origVolatiles csvMETH volatilesCsRbBaSrLaCePrNdSmEuGdTbDyHoErTmYbLuYZrNbHfTaPbThUScVCrFeCoNiCuZnGaMoAsNaKRef trace1METH trace1RbBaSrLaCeNdSmEuGdDyErYbLuYZrNbPbThUScTiVCrNiCuZnGaRef trace2METH trace2Light csvHalogen csvother major csvother lile csvother ree csvother hfse csvother hpe csvother tm csvother misc csv
Jensen_2008_Chester_Bluff65.38-142.66997Jensen, B. J. L. Chester Bluff is located in Yukon Charley Rivers National Preserve (YCNP) in east-central Alaska, on the northwest bank of the Yukon River directly upstream from its confluence with the Charley River. It is a terrace comprising a series of individual bluffs dissected by gullies that extend laterally for about 3 km. The south-facing bluffs are dry and substantial excavation (>2m) is needed to reach frozen sediments. Chester Bluff can be broadly differentiated into four units. The base of the bluff is a bedrock terrace exposed up to ~10 m above river level, composed of argillite, part of the Cretaceous Biederman Formation. Deposited on the terrace are 8-10 m of paleo-Yukon River gravel, which are overlain by 5-10 m of sand and silt rhythmites with minor gravel and planar-bedded sand. Up to 40 m of silt, interpreted as loess and interbedded with multiple organic horizons and tephra beds, cap the sequence. Sites A through C were visited in the area and were found to host 19 distinct tephra beds. A near vertical slope at Site A prevented trench completion. Two trenches were excavated on either side of Site A to examine the lateral continuity of tephra beds. Site B was successfully logged from the top of the bluff to the upper-most sand unit associated with the flood deposits. Thick colluvium at Site C prevented completion of the trench at this site. No coordinates provided; location imprecisely georeferenced from Figure 1 in Jensen et al. (2008).Only present at Site B of Chester Bluff. 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. A single isolated white pod of the YT tephra, 1.5 cm thick and 3 cm long, was found 20 cm above BC in a thick fibrous organic bed. Appears to have a low percentage of phenocrysts. Its glass morphology is predominantly chunky glass shards and pumice, with rare frothy pumice. Glass is commonly brown and rich in microcrysts. Phenocrysts are dominated by ortho-pyroxene, green amphibole is present but rare. The composition reported was calculated from analyses of one sample: UA1232.Jensen_2008_Chester_Bluff_Yukon_Tanana_tephra-P1Tephra FallCumulateGlass 79.55 0.31 11.41 0.93 0.03 0.13 0.44 3.5 3.65 6162EMP0.93Cl=0.04; H2O=4.87EMP

SAMPLE LOCATION

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