Physical and chemical evidence of the 1850 Ma Sudbury impact event in the Baraga Group, Michigan

An ejecta layer produced by the Sudbury impact event ca. 1850 Ma occurs within the Baraga Group of northern Michigan and provides an excellent record of impact-related depositional processes. This newly discovered, ∼2-4-m-thick horizon accumulated in a peritidal environment during a minor sea-level...

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Bibliographic Details
Published in:Geology (Boulder) 2007-09, Vol.35 (9), p.827-830
Main Authors: Pufahl, Peir K, Hiatt, Eric E, Stanley, Clifford R, Morrow, Jared R, Nelson, Gabriel J, Edwards, Cole T
Format: Article
Language:English
Subjects:
Baraga Group
chronostratigraphy
clasts
coastal environment
cores
depositional environment
ejecta
geochemistry
Great Lakes region
impacts
intertidal environment
iridium
key beds
Marine
marker beds
Marquette County Michigan
metals
metamorphic rocks
metamorphism
metasedimentary rocks
Michigan
Michigan Upper Peninsula
microstructure
North America
platinum group
Precambrian
Proterozoic
reworking
rhodium
rock, sediment, soil
sea-level changes
shock metamorphism
Stratigraphy
Sudbury ejecta
tsunamis
United States
upper Precambrian
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Summary:An ejecta layer produced by the Sudbury impact event ca. 1850 Ma occurs within the Baraga Group of northern Michigan and provides an excellent record of impact-related depositional processes. This newly discovered, ∼2-4-m-thick horizon accumulated in a peritidal environment during a minor sea-level lowstand that punctuated a period of marine transgression. Common ejecta clasts include shock-metamorphosed quartz grains, splash-form melt spherules and tektites, accretionary lapilli, and glassy shards, suggesting sedimentation near the terminus of the continuous ejecta blanket. Sedimentologic and geochemical data indicate that primary fallout from a turbulent ejecta cloud was reworked to varying degrees by an impact-generated tsunami wave train. Observed platinum group element anomalies (Ir, Rh, and Ru) within the Sudbury ejecta horizon are sufficient to suggest that the impactor was a meteorite. Documenting and interpreting the detailed characteristics of the Sudbury ejecta horizon in Michigan have yielded a fingerprint to identify this chronostratigraphic marker in other Paleoproterozoic basins. For the first time a foundation exists to assess the consequences of the Sudbury impact on Precambrian ocean chemistry and early life.
ISSN:0091-7613
DOI:10.1130/G23751A.1