Abstract

In mapping and correlating post-Laramie formations in the Denver Basin, clear-cut mappable formation boundaries have been defined and used.

It is proposed that

  • (1) the Laramie-Arapahoe contact remain as originally defined by Emmons, Cross, and Eldridge (1896);

  • (2) the Arapahoe-Denver contact be placed at the widespread erosional disconformity at the base of the lowest, thickest, and most prominent basalt-andesite pebble conglomerate bed in the Denver area, instead of at the first appearance of andesitic debris as originally proposed by Emmons, Cross, and Eldridge (1896).

The following changes in nomenclature are proposed:

  • (1) The Arapahoe and Denver formations can be mapped throughout the Denver Basin, and these names should replace the term “lower Dawson” of Dane and Pierce (1936).

  • (2) “Dawson formation” (type section at Dawson Butte) should designate only “upper Dawson” of Dane and Pierce.

  • (3) The name “Green Mountain conglomerate” should be abandoned as it is only a partial representative of the proposed Dawson formation as restricted in (2).

  • (4) The Laramie formation should be restricted to its original definition by Emmons, Cross, and Eldridge (1896) rather than extended as proposed by Brown (1943).

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