HR: 0800h
AN: V31B-0496    [Abstracts]
TI: Extending the map coverage of the Hayes Tephra set, an important Late Holocene Marker Horizon for South Central Alaska.
AU: * Hagel, L A
EM: lynetta11@aol.com
AF: Department of Geology, University of Alaska, Anchorage, 3211 Providence Dr., Anchorage, AK 99507, United States
AU: Wallace, K L
EM: kwallace@usgs.gov
AF: U.S. Geological Survey, Alaska Science Center, Alaska Volcano Observatory, 4230 Unversity Dr., Suite 201, Anchorage, AK 99508, United States
AU: McIntire, J
EM: mcintire@usgs.gov
AF: U.S. Geological Survey, Alaska Science Center, Alaska Volcano Observatory, 4230 Unversity Dr., Suite 201, Anchorage, AK 99508, United States
AB: Hayes volcano produced a set of closely spaced tephra-fall deposits in the late Holocene that are recognized as the most widespread and volumetrically significant of Holocene tephra-fall deposits in South Central Alaska. Riehle (1985) first documented the Hayes Tephra set as originating from Hayes volcano in the Tordrillo Mountains, 150 km northwest of Anchorage. He recognized between 7 and 8 deposits covering a time period of about 300 years (3500-3800 yr BP). Although the set of tephra deposits has a unique phenocryst assemblage (rare biotite and high proportions of amphibole to pyroxene), individual fall-layers within the set are not easily distinguishable and the thickness and number of individual layers varies from site to site. Thus the Hayes Tephra set is most often considered a single, nearly isochronous marker horizon. Riehle et al. (1990) produced an isopach map of the Hayes Tephra set that included a few distal stations 225-440 km from the vent, but with limited coverage isopach lines are mostly uncertain. Beget et al. (1991) correlated formally and informally named tephra beds, Jarvis Ash Bed, Tangle Lakes tephra, and Cantwell Ash Bed to the Hayes Tephra set, thereby extending the distribution of the Hayes Tephra set into central Alaska (475 km from the vent). We have conducted a careful literature search of published and unpublished materials from archeological and geological reports documenting other named tephra that are correlative to the Hayes Tephra set. Informal names of tephra correlative with the Hayes set are numerous and have complicated interpretations of the distribution to this important marker horizon. Available data are compiled as a map coverage using Arc GIS to show all locations and sample information for documented Hayes tephra. In addition, nine new sample localities for the Hayes Tephra set have been added to the map coverage based on new fieldwork. Together, these data better constrain the distribution of the Hayes Tephra set thereby providing a valuable tool for solving geochronometric problems in this region. Riehle, J.R. (1985). A reconnaissance of the major Holocene tephra deposits in the upper Cook Inlet region, Alaska. Journal of Volcanology and Geothermal Research 26, 37-74. Riehle, J.R., Bowers, P.M., and Ager, T.A. (1990). The Hayes tephra deposits, an upper Holocene marker horizon in south-central Alaska. Quaternary Research 33, 276-290. Beget, J.E., Reger, R.D., Pinney, D., Gillispie, T., and Campbell, K. (1991). Correlation of the Holocene Jarvis Creek, Tangle Lakes, Cantwell, and Hayes Tephras in south-central and central Alaska. Quaternary Research 35, 174-189.
DE: 1145 Tephrochronology (8455)
DE: 8404 Volcanoclastic deposits
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting