HR: 0800h
AN: C51A-0072    [Abstracts]
TI: The Present ice age: A 5 Million Year Record of Glacial-Interglacial Oscillations Based on Volcanic Strata in Skaftafell, SE-Iceland
AU: * Helgason, J
EM: jhelgason@internet.is
AF: National Land Survey of Iceland, Stillholt 14, Akranes, 300, Iceland
AU: Duncan, R
EM: rduncan@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AB: Stratigraphic, paleomagnetic and Ar-Ar age dating of 5 km thick overlapping volcanic sections in Skaftafell, SE- Iceland, has revealed close to 16 glacial-interglacial transitions during the last 5 m. y. Extensive mapping has provided a detailed window into the onset and evolution of the present ice age that intensified at roughly 3 Ma. Lithology of volcanic strata provided means to distinguish glacial and interglacial conditions. Volcanic strata that accumulated under ice free conditions is mapped as widespread lava formations whereas subglacially formed volcanics piled up on top of volcanic fissures. Through magnetostratigraphic work and Ar-Ar age dating correlations were made with the geomagnetic time scale to further constrain timing of events. The lowest part of the section consists of lavas that formed when erosion was minimal and the area had remained virtually ice free over an extended period. The earliest tillites in the area are dated at 4.0 Ma and a thick hyaloclastite horizon is dated at 3.2 Ma. Roughly at 2.6 Ma the record shows evidence of frequent glaciations. The predominantly normal Gauss magnetic polarity chron (2.33-3.35 Ma) plays a major role in mapping the ice age onset as units below consist of reversely magnetized lavas deposited during the late Gilbert magnetic polarity chron (3.35-3.82 Ma). Through field mapping erosional horizons have been traced that show deepening of valleys from roughly 100 m during early Gauss to at least 350 m at 1.7 Ma, and to over 2000 m at present.
UR: http://www.skaftafell.org
DE: 1520 Magnetostratigraphy
DE: 1815 Erosion
DE: 5416 Glaciation
DE: 8427 Subaqueous volcanism
SC: Cryosphere [C]
MN: 2007 Fall Meeting