Drum Sheep Creek Tephra-C, K, A
Start: 80000 yBP [1]
Event Type: Explosive
Description: From Westgate and others (2007): "‘SCt’ refers to a family of tephra beds that closely resemble one another in their petrographic and compositional characteristics. Its members are named as follows: SCt-F (Fairbanks, Alaska, e.g. UT734), SCt-CC (Canyon Creek, Alaska, e.g. UT250), SCt-C (western Yukon, e.g. UT2096), SCt-K (western Yukon, e.g. UT1052), and SCt-A (western Yukon, e.g. UT1051)."
"Sheep Creek-K tephra is widely distributed across the Klondike goldfields (Fig. 7, Table 1 [in original text]), and is present at Lost Chicken, Alaska, Soya Pup, Thistle Creek, and Stewart River localities, Yukon (Figs. 1 and 8 [in original text]). Sheep Creek-C tephra occurs at Dominion Creek (Fig. 7, locality 16 [in original text]), where it is found on the surface of a forest bed, exactly the same stratigraphic setting as at Ash Bend site (Fig. 8, locality 21, UT2096). SCt-A (Ash Bend tephra) is also at Ash Bend, Yukon."
"SCt [Sheep Creek Tephra] is now known to be made up of several stratigraphic units: SCt-F (Fairbanks, Alaska; 200 ka), SCt-CC (Canyon Creek, Alaska), and in the western Yukon, SCt-C, SCt-K (80 ka), and SCt-A. Beds C, K, and A must be similar in age because of their close stratigraphic association at Ash Bend in Yukon. Compositional and temporal controls, including Sr isotopes, suggest Mount Drum in the Wrangell volcanic field as the source of the SCt beds."
"Assuming Mount Drum is the source of the younger SCt beds, renewed volcanic activity must have started prior to 80 ka, the age of SCt-K, and probably as early as 100 ka, given the palaeoenvironmental setting of the older SCt-C bed at Ash Bend-namely, boreal forest conditions of the last interglacial (Schweger, 2003 ). During this later phase of activity, tephra fallout was directed to the northeast across easternmost Alaska and western Yukon."
"The presence of glass shards of SCt-C composition in SCt-K samples and glass shards of SCt-K composition in the SCt-A sample suggest these beds come from the same volcano. Systematic differences between these three tephra beds also suggest a close genetic relationship."
"Occurrences of SCt in Yukon are presently restricted to the western Yukon, specifically, the Klondike district near Dawson City, Thistle Creek, Soya Pup, and the lower stretch of the Stewart River (Figs. 1, 7, 8, and Table 1 [in original text]). The most important section is on the Stewart River at Ash Bend (Fig. 8, locality 21 [in original text]) where SCt is found in association with two other tephra beds (Fig. 9 [in original text]). All three tephra beds occur within the sedimentary fill of a channel cut into the Reid glacial drift (Westgate and others, 2001). The exposure in 1999 showed the basal channel-fill sediments to consist of organic-rich silts (unit 4 [in original text]) with transported spruce logs and vertebrate fossils. SCt ([sample] UT1052) occurs in the overlying silts (unit 5 [in original text]), which contain less organic material, and the very thin Ash Bend tephra ([sample] UT1051) occurs in the lower part of unit 6-90 cm above SCt-in a coarsening-upward sequence of largely inorganic silt and sand (Fig. 9 [in original text]). Major slumping at the downstream end of the Ash Bend site in 2005 revealed a thicker channel-fill sequence including SCt with a new tephra bed ([sample] UT2096) 6.5 m below within the organic-rich sediments (Fig. 9B [in original text])."
"SCt ([sample] UT1052) at Ash Bend contains a white, frothy pumice similar to that of the Fairbanks occurrences with the exception that trace amounts of a low vesicular glass and bubble-wall shards are present. The mineral assemblage likewise resembles SCt at Fairbanks being dominated by plagioclase and hornblende with lesser amounts of ilmenite and magnetite. Hypersthene is scarce and slightly- to non-pleochroic-that is, different from the variety in SCt at Fairbanks and Canyon Creek. Apatite, clinopyroxene and quartz occur in trace quantities. The glass composition of SCt at Ash Bend falls within the envelope on the K2O-SiO2 plot defined by SCt samples from Fairbanks and Yukon (Fig. 6 [in original text]). The petrographic features of Ash Bend tephra ([sample] UT1051) closely resemble those of the SCt bed from the same site. However, its glass is distinctly less silicic (Fig. 6, Table 2 [in original text])."
"Sheep Creek-K tephra is widely distributed across the Klondike goldfields (Fig. 7, Table 1 [in original text]), and is present at Lost Chicken, Alaska, Soya Pup, Thistle Creek, and Stewart River localities, Yukon (Figs. 1 and 8 [in original text]). Sheep Creek-C tephra occurs at Dominion Creek (Fig. 7, locality 16 [in original text]), where it is found on the surface of a forest bed, exactly the same stratigraphic setting as at Ash Bend site (Fig. 8, locality 21, UT2096). SCt-A (Ash Bend tephra) is also at Ash Bend, Yukon."
"SCt [Sheep Creek Tephra] is now known to be made up of several stratigraphic units: SCt-F (Fairbanks, Alaska; 200 ka), SCt-CC (Canyon Creek, Alaska), and in the western Yukon, SCt-C, SCt-K (80 ka), and SCt-A. Beds C, K, and A must be similar in age because of their close stratigraphic association at Ash Bend in Yukon. Compositional and temporal controls, including Sr isotopes, suggest Mount Drum in the Wrangell volcanic field as the source of the SCt beds."
"Assuming Mount Drum is the source of the younger SCt beds, renewed volcanic activity must have started prior to 80 ka, the age of SCt-K, and probably as early as 100 ka, given the palaeoenvironmental setting of the older SCt-C bed at Ash Bend-namely, boreal forest conditions of the last interglacial (Schweger, 2003 ). During this later phase of activity, tephra fallout was directed to the northeast across easternmost Alaska and western Yukon."
"The presence of glass shards of SCt-C composition in SCt-K samples and glass shards of SCt-K composition in the SCt-A sample suggest these beds come from the same volcano. Systematic differences between these three tephra beds also suggest a close genetic relationship."
"Occurrences of SCt in Yukon are presently restricted to the western Yukon, specifically, the Klondike district near Dawson City, Thistle Creek, Soya Pup, and the lower stretch of the Stewart River (Figs. 1, 7, 8, and Table 1 [in original text]). The most important section is on the Stewart River at Ash Bend (Fig. 8, locality 21 [in original text]) where SCt is found in association with two other tephra beds (Fig. 9 [in original text]). All three tephra beds occur within the sedimentary fill of a channel cut into the Reid glacial drift (Westgate and others, 2001). The exposure in 1999 showed the basal channel-fill sediments to consist of organic-rich silts (unit 4 [in original text]) with transported spruce logs and vertebrate fossils. SCt ([sample] UT1052) occurs in the overlying silts (unit 5 [in original text]), which contain less organic material, and the very thin Ash Bend tephra ([sample] UT1051) occurs in the lower part of unit 6-90 cm above SCt-in a coarsening-upward sequence of largely inorganic silt and sand (Fig. 9 [in original text]). Major slumping at the downstream end of the Ash Bend site in 2005 revealed a thicker channel-fill sequence including SCt with a new tephra bed ([sample] UT2096) 6.5 m below within the organic-rich sediments (Fig. 9B [in original text])."
"SCt ([sample] UT1052) at Ash Bend contains a white, frothy pumice similar to that of the Fairbanks occurrences with the exception that trace amounts of a low vesicular glass and bubble-wall shards are present. The mineral assemblage likewise resembles SCt at Fairbanks being dominated by plagioclase and hornblende with lesser amounts of ilmenite and magnetite. Hypersthene is scarce and slightly- to non-pleochroic-that is, different from the variety in SCt at Fairbanks and Canyon Creek. Apatite, clinopyroxene and quartz occur in trace quantities. The glass composition of SCt at Ash Bend falls within the envelope on the K2O-SiO2 plot defined by SCt samples from Fairbanks and Yukon (Fig. 6 [in original text]). The petrographic features of Ash Bend tephra ([sample] UT1051) closely resemble those of the SCt bed from the same site. However, its glass is distinctly less silicic (Fig. 6, Table 2 [in original text])."
References Cited
[1] Changing ideas on the identity and stratigraphic significance of the Sheep Creek tephra beds in Alaska and the Yukon Territory, northwestern North America, 2008
Westgate, J.A., Preece, S.J., Froese, D.G., Pearce, N.J.G., Roberts, R.G., Demuro, M., Hart, W.K., and Perkins, W., 2008, Changing ideas on the identity and stratigraphic significance of the Sheep Creek tephra beds in Alaska and the Yukon Territory, northwestern North America: Quaternary International, v. 178, n. 1, p. 183-209, doi: 10.1016/j.quaint.2007.03.009.[2] Dating Early and Middle (Reid) Pleistocene glaciations in central Yukon by tephrochronology, 2001
Westgate, J.A., Preece, S.J., Froese, D.G., Walter, R.C., Sandhu, A.S., and Schweger, C.E., 2001, Dating Early and Middle (Reid) Pleistocene glaciations in central Yukon by tephrochronology: Quaternary Research, v. 56, n. 3, p. 335-348, doi: 10.1006/qres.2001. 2274 .[3] Characterization, identity, distribution, and source of late Cenozoic tephra beds in the Klondike District of the Yukon, Canada, 2000
Preece, S. J., Westgate, J. A., Alloway, B. V., and Milner, M. W., 2000, Characterization, identity, distribution, and source of late Cenozoic tephra beds in the Klondike District of the Yukon, Canada: Canadian Journal of Earth Sciences, v. 37, n. 7, p. 983-996.[4] Late Cenozoic geology, Ancient Pacific Margin NATMAP Project, report 5: paleoecology and proxy climatic change records, south Klondike placer region, Yukon Territory, 2002
Jackson Jr., L.E., Froese, D.G., Telka, A.M., Westgate, J.A., Preece, S.J., Storer, J.E., and Huscroft, C.A., 2002, Late Cenozoic geology, Ancient Pacific Margin NATMAP Project, report 5: paleoecology and proxy climatic change records, south Klondike placer region, Yukon Territory: Geological Survey of Canada, Currrent Research, 2002-A2, 16 p.[5] Late Cenozoic history of McQuesten map area, Yukon Territory, with applications to placer gold research, 1997
Bond, J.D., 1997, Late Cenozoic history of McQuesten map area, Yukon Territory, with applications to placer gold research: University of Alberta, Edmonton, unpublished M.S. thesis, 161 p.[6] Continuous late Quaternary proxy climate records from loess in Beringia, 2001
Beget, J. E., 2001, Continuous late Quaternary proxy climate records from loess in Beringia: Quaternary Science Reviews, v. 20, n. 1-3, p. 499-507.[7] The Klondike goldfields and Pleistocene environments of Beringia, 2009
Froese, D.G., Zazula, G.D., Westgate, J.A., Preece, S.J., Sanborn, P.T., Reyes, A.V., Pearce, N.J.G., 2009, The Klondike goldfields and Pleistocene environments of Beringia: GSA Today, v. 19, n. 4, p. 4-10.[8] Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek Tephra, northwestern North America, 2003
Schweger, C. E., 2003, Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek Tephra, northwestern North America: in Westgate, J. A., (ed.), Special issue dedicated to Troy Pewe, Quaternary Research, v. 60, n. 1, p. 44-49.[9] Ash Bend Section, 1987
Hughes, O.L., Harington, C.R., Schweger, C.E., and Matthews, J.V. Jr., 1987, Ash Bend Section, in Morison, S.R, and Smith, C.A.S., eds., Guidebook to Quaternary research in Yukon: XII INQUA Congress, Ottawa, Canada, National Research Council, Ottawa, Ontario, p. 50-53.[10] Fullglacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada, 2006
Sanborn, P.T., Smith, C.A.S., Froese, D.G., Zazula, G.D., Westgate, J.A., 2006, Fullglacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada: Quaternary Research, v. 66, p. 147-157.Complete Eruption References
Changing ideas on the identity and stratigraphic significance of the Sheep Creek tephra beds in Alaska and the Yukon Territory, northwestern North America, 2008
Westgate, J.A., Preece, S.J., Froese, D.G., Pearce, N.J.G., Roberts, R.G., Demuro, M., Hart, W.K., and Perkins, W., 2008, Changing ideas on the identity and stratigraphic significance of the Sheep Creek tephra beds in Alaska and the Yukon Territory, northwestern North America: Quaternary International, v. 178, n. 1, p. 183-209, doi: 10.1016/j.quaint.2007.03.009.
Dating Early and Middle (Reid) Pleistocene glaciations in central Yukon by tephrochronology, 2001
Westgate, J.A., Preece, S.J., Froese, D.G., Walter, R.C., Sandhu, A.S., and Schweger, C.E., 2001, Dating Early and Middle (Reid) Pleistocene glaciations in central Yukon by tephrochronology: Quaternary Research, v. 56, n. 3, p. 335-348, doi: 10.1006/qres.2001. 2274 .
Characterization, identity, distribution, and source of late Cenozoic tephra beds in the Klondike District of the Yukon, Canada, 2000
Preece, S. J., Westgate, J. A., Alloway, B. V., and Milner, M. W., 2000, Characterization, identity, distribution, and source of late Cenozoic tephra beds in the Klondike District of the Yukon, Canada: Canadian Journal of Earth Sciences, v. 37, n. 7, p. 983-996.
Late Cenozoic geology, Ancient Pacific Margin NATMAP Project, report 5: paleoecology and proxy climatic change records, south Klondike placer region, Yukon Territory, 2002
Jackson Jr., L.E., Froese, D.G., Telka, A.M., Westgate, J.A., Preece, S.J., Storer, J.E., and Huscroft, C.A., 2002, Late Cenozoic geology, Ancient Pacific Margin NATMAP Project, report 5: paleoecology and proxy climatic change records, south Klondike placer region, Yukon Territory: Geological Survey of Canada, Currrent Research, 2002-A2, 16 p.
Continuous late Quaternary proxy climate records from loess in Beringia, 2001
Beget, J. E., 2001, Continuous late Quaternary proxy climate records from loess in Beringia: Quaternary Science Reviews, v. 20, n. 1-3, p. 499-507.
Late Cenozoic history of McQuesten map area, Yukon Territory, with applications to placer gold research, 1997
Bond, J.D., 1997, Late Cenozoic history of McQuesten map area,
Yukon Territory, with applications to placer gold research: University of Alberta, Edmonton, unpublished M.S. thesis, 161 p.
The Klondike goldfields and Pleistocene environments of Beringia, 2009
Froese, D.G., Zazula, G.D., Westgate, J.A., Preece, S.J., Sanborn, P.T., Reyes, A.V., Pearce, N.J.G., 2009, The Klondike goldfields and Pleistocene environments of Beringia: GSA Today, v. 19, n. 4, p. 4-10.
Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek Tephra, northwestern North America, 2003
Schweger, C. E., 2003, Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek Tephra, northwestern North America: in Westgate, J. A., (ed.), Special issue dedicated to Troy Pewe, Quaternary Research, v. 60, n. 1, p. 44-49.
Ash Bend Section, 1987
Hughes, O.L., Harington, C.R., Schweger, C.E., and Matthews, J.V. Jr., 1987, Ash Bend Section, in Morison, S.R, and Smith, C.A.S., eds., Guidebook to Quaternary research in Yukon: XII INQUA Congress, Ottawa, Canada, National Research Council, Ottawa, Ontario, p. 50-53.
Fullglacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada, 2006
Sanborn, P.T., Smith, C.A.S., Froese, D.G., Zazula, G.D., Westgate, J.A., 2006, Fullglacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada: Quaternary Research, v. 66, p. 147-157.
