2011 GSA Annual Meeting in Minneapolis (912 October 2011)
441 Thursday, 13 October 2011
7:30 AM-7:00 PM, Minneapolis Convention Center: Ballroom A Foyer, 2nd Ave. Entrance

Sudbury Meteorite Impact Layer in the Western Lake Superior Region

Primary Leader: Mark A. Jirsa
Leader(s): Philip Fralick, Paul W. Weiblen, Jennifer L.B. Anderson
Field Trip Description: This trip examines a sequence of ejecta and deformed substrate resulting from the 1850 Ma Sudbury meteorite impact. Of the 178 verified terrestrial impacts, the Sudbury event was the second largest (based on estimated crater size) and forth oldest. An impact origin for the Sudbury structure in Ontario has long been accepted; however, the resulting ejecta blanket was discovered only recently in 2005 and informally named the "Sudbury impact layer." In the western Lake Superior region, the layer lies at the stratigraphic top of Paleoproterozoic Gunflint Iron Formation, 700 kilometers west of the impact site. The trip will visit exposures at Gunflint Lake in NE Minnesota, at the edge of the Boundary Waters Canoe Area Wilderness, and near Thunder Bay, Ontario. The deposits include autochthonous material interpreted to be seismically folded and shattered iron-formation, and overlying strata composed largely of allochthonous material derived in part from target rocks. Definitive evidence of an impact origin includes the occurrence of accretionary lapilli, pellets, spherules, relict glass, and quartz fragments marked by planar deformation features. The Sudbury impact layer exhibits extreme lithologic variability from place to place within each exposure area and between exposure areas, which is not surprising given the chaotic nature of impact. The stratigraphy presented by these exposures can be used to devise a sequence of deformational and depositional events that is consistent with experimental and empirical evidence of impact processes.
Field Trip will span: 3 days
Sponsor(s): Planetary Geology Division (via David Williams' approval)

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