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SAMPLE INFO : Jensen_2008_Chester_Bluff_Charley_River_tephra
Sample ID:Jensen_2008_Chester_Bluff_Charley_River_tephra
Station ID:Jensen_2008_Chester_Bluff
Latitude:65.38
Longitude:-142.66997
Datum:NAD83
Sample Type 1:Tephra Fall
 Text Description:
Present at all three sites of Chester Bluff, Site A, Site B, and Site C. Lowermost tephra, found at all sites. It forms pods up to 4 cm thick and 10 cm long and tends to have an orange-pink cast when within organic sediments, although it can also be white. CR is reworked into, or directly above, fissile organic-rich silt. The lateral continuity of CR across the bluffs suggests that CR was deposited when the site was relatively level and loess had not aggraded and/or been incised enough to form a complex gully-bluff network like the one that is seen today. The different sequence of tephra beds above CR at each site suggests the presence of one or more unconformities above the tephra bed. 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 fourteen samples: UA1052, UA1053, UA1054, UA1064, UA1078, UA1092, UA1093, UA1094, UA1095, UT1878, UT1880, UT1889, UT1667, and UA1234.

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.< 780000 stratigraphy; 10291; Age based on magnetic polarity of the sediments.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).Present at all three sites of Chester Bluff, Site A, Site B, and Site C. Lowermost tephra, found at all sites. It forms pods up to 4 cm thick and 10 cm long and tends to have an orange-pink cast when within organic sediments, although it can also be white. CR is reworked into, or directly above, fissile organic-rich silt. The lateral continuity of CR across the bluffs suggests that CR was deposited when the site was relatively level and loess had not aggraded and/or been incised enough to form a complex gully-bluff network like the one that is seen today. The different sequence of tephra beds above CR at each site suggests the presence of one or more unconformities above the tephra bed. 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 fourteen samples: UA1052, UA1053, UA1054, UA1064, UA1078, UA1092, UA1093, UA1094, UA1095, UT1878, UT1880, UT1889, UT1667, and UA1234.Jensen_2008_Chester_Bluff_Charley_River_tephraTephra FallCumulateGlass 72.26 0.23 15.85 1.8 0.08 0.6 2.11 4.56 2.45 6162EMP1.8Cl=0.06; H2O=5.32EMP

SAMPLE LOCATION

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