Abstract

Potassium-argon dating of glaucony, one of the few widely occurring authigenic materials in the sedimentary record, has provided a large percentage of the dates used for the calibration of the geologic time scale. This material has been considered unsuitable for 40Ar-39Ar dating because of the large losses of neutron-induced 39Ar during or subsequent to irradiation of samples. We have measured recoiled 39Ar and 37Ar from single grains of glaucony (100-350 μm in diameter). Irradiations were done both in air and in vacuo by using a microampoule technique of encapsulation. The observed in vacuo behavior of recoiled atoms can be readily understood by a simple model of their interaction with the network of very fine laminae composing the grains. When the microampoule technique is used, the integrated 40Ar-39Ar ages and their associated precision compare very favorably with conventional K-Ar results. Because glauconies are inherently heterogeneous populations, owing to their complex evolution, it is anticipated that single-grain 40Ar-39Ar dating may lead to significant refinements in the geologic time scale, especially for the Cenozoic.

First Page Preview

First page PDF preview
You do not currently have access to this article.