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Sudbury impact layer in the western Lake Superior region

Mark A. Jirsa, Philip W. Fralick, Paul W. Weiblen and Jennifer L. B. Anderson
Sudbury impact layer in the western Lake Superior region (in Archean to Anthropocene; field guides to the geology of the Mid-Continent of North America, James D. Miller (editor), George J. Hudak (editor), Chad Wittkop (editor) and Patrick I. McLauglin (editor))
Field Guide (Geological Society of America) (September 2011) 24: 147-169


This field trip examines a sequence of ejecta and deformed substrate resulting from the 1850 Ma meteorite impact. An impact origin for the Sudbury structure in Ontario has long been accepted, but knowledge of the corresponding ejecta was limited to fall-back breccia in the relict crater at Sudbury. The more distant ejecta blanket was discovered only recently near Thunder Bay, Ontario, and later in other parts of the Lake Superior region. Known informally as the Sudbury impact layer (SIL), it occurs at and near the stratigraphic top of Paleoproterozoic iron-formation. The impact-related deposits in the western Lake Superior region include (1) autochthonous material interpreted to be seismically folded and shattered iron-formation and carbonate rocks (breccia), overlain by (2) strata composed largely of allochthonous material (ejecta) derived in part from target rocks, and (3) irregular layers that appear to be mixtures of locally and distally derived material. Definitive microscopic evidence of an impact origin includes the occurrence of accretionary lapilli, ash pellets, spherules, devitrified glass, and quartz fragments marked by planar deformation features. The SIL exhibits extreme lithologic variability from place to place within each exposure area and between exposure areas. Nevertheless, the stratigraphic relationships that are presented by these exposures can be used to devise a sequence of deformation and depositional events that is largely consistent with experimental and empirical evidence of impact processes. This field trip will demonstrate that the stratigraphic arrangement of facies in the SIL has important temporal implications for understanding mechanisms of ejecta delivery and deposition.

ISSN: 2333-0937
EISSN: 2333-0945
Serial Title: Field Guide (Geological Society of America)
Serial Volume: 24
Title: Sudbury impact layer in the western Lake Superior region
Title: Archean to Anthropocene; field guides to the geology of the Mid-Continent of North America
Author(s): Jirsa, Mark A.Fralick, Philip W.Weiblen, Paul W.Anderson, Jennifer L. B.
Author(s): Miller, James D.editor
Author(s): Hudak, George J.editor
Author(s): Wittkop, Chadeditor
Author(s): McLauglin, Patrick I.editor
Affiliation: Minnesota Geological Survey, St. Paul, MN, United States
Affiliation: University of Minnesota-Duluth, Department of Geological Sciences, Duluth, MN, United States
Pages: 147-169
Published: 201109
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 46
Accession Number: 2012-009898
Categories: StratigraphySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch maps
N48°00'00" - N48°10'00", W90°52'60" - W90°45'00"
Secondary Affiliation: Natural Resources Research Institute, USA, United StatesMinnesota State University, USA, United StatesWisconsin Geological and Natural History Survey, USA, United StatesLakehead University, USA, United StatesUniversity of Minnesota, USA, United StatesWinona State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201205
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