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SAMPLE INFO : Jensen_2008_Chester_Bluff_Old_Crow_tephra
Sample ID:Jensen_2008_Chester_Bluff_Old_Crow_tephra
Station ID:Jensen_2008_Chester_Bluff
Latitude:65.38
Longitude:-142.66997
Datum:NAD83
Sample Type 1:Tephra Fall
 Text Description:
Present at Site B and Site C of Chester Bluff. At Site B, the OC tephra is separated from a >/~ 1 m thick organic unit overlying the th BS tephra by 5m of remobilized, massive, inorganic loess. OC is up to 25 cm thick and continuous across the bluff. The base of the tephra has a sharp contact and is Fe-stained; the upper contact is diffuse and partially reworked. At Site C, the OC is present approximately 30m downstream from the main stratigraphic section. It is up to 10 cm thick and heavily reworked within dark brown organic-rich silt. OC can be traced laterally for over 10 m, and rises steeply towards the top of the upstream end of the bluff. Although OC could not be traced to the main excavated trench at Site C, its projected position stratigraphically overlies BT. Low vesicular pumice, bubble-walled and tri-cuspate shards. The composition reported was calculated from analyses of three samples: UA1099, UA1233, and UA1211.

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. 124000 ± 10000 known unit; 10271; Age is approximate. Revised glass fission-track age with re-calibration; four Old Crow Tephra sample glass fission-track ages (UT1434, UT613, UT501, UT613).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 Site B and Site C of Chester Bluff. At Site B, the OC tephra is separated from a >/~ 1 m thick organic unit overlying the th BS tephra by 5m of remobilized, massive, inorganic loess. OC is up to 25 cm thick and continuous across the bluff. The base of the tephra has a sharp contact and is Fe-stained; the upper contact is diffuse and partially reworked. At Site C, the OC is present approximately 30m downstream from the main stratigraphic section. It is up to 10 cm thick and heavily reworked within dark brown organic-rich silt. OC can be traced laterally for over 10 m, and rises steeply towards the top of the upstream end of the bluff. Although OC could not be traced to the main excavated trench at Site C, its projected position stratigraphically overlies BT. Low vesicular pumice, bubble-walled and tri-cuspate shards. The composition reported was calculated from analyses of three samples: UA1099, UA1233, and UA1211.Jensen_2008_Chester_Bluff_Old_Crow_tephraTephra FallCumulateGlass 75.23 0.3 13.08 1.77 0.06 0.28 1.54 3.75 3.7 6162EMP1.77Cl=0.28; H2O=4.59EMP

SAMPLE LOCATION

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