K-Ar and 40Ar/39Ar ages of tuff beds at Ocean Point on the Colville River, Alaska

J. E. Conrad, E. H. McKee, B. D. Turrin

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3 Scopus citations


The age of dinosaur-bone-bearing beds of the Prince Creek Formation along the Colville River has been in debate for the past decade. The need to resolve this conflict by accurately dating these strata is of greater than normal interest to the geologic community because a Paleocene age for dinosaurs would cast doubt on the bolide impact theory for the extinction of dinosaurs (and many other taxa) at the end of the Cretaceous Period. A number of tuff beds in the bluffs on the south side of the Colville River about 7 km west of Ocean Point contain glass shards suitable for dating by the K-Ar and the 40Ar/39Ar methods. Four samples of glass were dated by K-Ar and eight were dated by the 40Ar/39Ar incremental heating technique. The location of the Cretaceous-Tertiary boundary, considered to be at about 66 Ma, appears to be at least 100 m above the youngest dated tephra bed (M86LPA9), provided depositional and environmental conditions remained constant. This new dating, by establishing a Late Cretaceous age for the dinosaur-bone-bearing beds, is therefore compatible with the impact theory for the extinction of the dinosaurs. -from Authors

Original languageEnglish (US)
Pages (from-to)77-82
Number of pages6
JournalUS Geological Survey Bulletin
StatePublished - 1990
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geology


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