A reassessment of the age of the Hamilton Group, New York and Pennsylvania, and the role of inherited radiogenic Sr 87

Abstract

Statistical reassessment of the Rb-Sr data of Whitney and Hurley (1964) for the Middle Devonian Hamilton Group, New York and Pennsylvania, shows that the age can be more adequately represented by two parallel isochrons instead of the conventional one. Pooling of these two isochrons results in an apparent age of 384 ± 9 million yr for the Hamilton Group (using λRb 87 = 1.47 × 10 −11/ yr), with the possibility that this value could be reduced to 377 ± 11 million yr. These estimates fall within the presently suggested limits for the age of the Devonian. On the basis of these results there is no evidence to suggest that in general the application of total rock Rb-Sr age measurement techniques to argillaceous sediments yields results in excess of the true age of sedimentation.