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Summary of data on the age of the Orca Group, Alaska: A section in The United States Geological Survey in Alaska: Accomplishments during 1984

January 1, 1985

The Orca Group is a widespread, thick, complexly deformed accretionary sequence of flysch and tholeiitic basalt in the Prince William Sound area (Winkler, 1976; Winkler and Plafker, 1981) (fig. 49). Despite a number of extensive field studies of the Orca Group, reliable data on the age of the unit have been elusive. On the basis of sparse paleontologic and radiometric data, the sequence was regarded as Paleocene and early Eocene(?) age (Winkler and Plafker, 1981). New paleontologic data from fossil localities shown in figure 49 suggest that some strata assigned to the Orca Group are of middle Eocene age and possibly as young as late Eocene or Oligocene. However, data suggesting an age younger than about 50 Ma appear to be incompatible with radiometrically determined ages for plutons that intrude the Orca Group.

Publication Year 1985
Title Summary of data on the age of the Orca Group, Alaska: A section in The United States Geological Survey in Alaska: Accomplishments during 1984
DOI 10.3133/70180306
Authors George Plafker, Gerta Keller, Steven W. Nelson, Julie A. Dumoulin, Marti L. Miller
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Circular
Series Number 967
Index ID 70180306
Record Source USGS Publications Warehouse
USGS Organization Alaska Science Center; Alaska Science Center Geology Minerals