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SAMPLE INFO : Jensen_2008_Chester_Bluff_Biederman_tephra-P1
Sample ID:Jensen_2008_Chester_Bluff_Biederman_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 C of Chester Bluff. The Biederman tephra (BT) is up to 2 cm thick at Site C, forms pods up to 10 cm long, is continuous over 8m and has a salt and pepper appearance. It either rests directly on the surface of or is reworked into the upper-most organic unit of this exposure. At the upstream end of the exposure the organic unit is over-thickened and locally draped into an ice wedge cast about 1.7m deep. The ice wedge cast fill includes 1m of reworked organic-rich loess, indicating the ice wedge melted out when organic material was accumulating on the surface and accumulation continued after the cast was filled. BT forms rare pods in the loess that fills the cast. At the downstream end of the exposure, BT can be traced at the same elevation until it is truncated by a modern gully. Generally has highly inflated pumice and is particularly rich in phenocrysts, which are overwhelmingly green amphibole. The composition reported was calculated from analyses of six samples: UT1884, UT1888, UT1681, UA1079, UA1080, and UA1081.

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 C of Chester Bluff. The Biederman tephra (BT) is up to 2 cm thick at Site C, forms pods up to 10 cm long, is continuous over 8m and has a salt and pepper appearance. It either rests directly on the surface of or is reworked into the upper-most organic unit of this exposure. At the upstream end of the exposure the organic unit is over-thickened and locally draped into an ice wedge cast about 1.7m deep. The ice wedge cast fill includes 1m of reworked organic-rich loess, indicating the ice wedge melted out when organic material was accumulating on the surface and accumulation continued after the cast was filled. BT forms rare pods in the loess that fills the cast. At the downstream end of the exposure, BT can be traced at the same elevation until it is truncated by a modern gully. Generally has highly inflated pumice and is particularly rich in phenocrysts, which are overwhelmingly green amphibole. The composition reported was calculated from analyses of six samples: UT1884, UT1888, UT1681, UA1079, UA1080, and UA1081.Jensen_2008_Chester_Bluff_Biederman_tephra-P1Tephra FallCumulateGlass 76.76 0.14 13.55 0.97 0.04 0.3 1.39 3.66 3.14 6162EMP0.97Cl=0.05; H2O=5.36EMP

SAMPLE LOCATION

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