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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 41 (1957)

Issue: 11. (November)

First Page: 2508

Last Page: 2518

Title: Ignacio Quartzite of Southwestern Colorado

Author(s): F. H. T. Rhodes (2), James H. Fisher (3)


The Ignacio quartzite of southwestern Colorado is referred to the Late Cambrian or Early Ordovician on the basis of the occurrence of oboloid brachiopods. This is contrary to the recent conclusion of Barnes (1954), but in support of the age provisionally assigned by earlier workers. A major unconformity occurs between the Ignacio and the overlying Elbert formation of Late Devonian age. The Ignacio was deposited on an eroded, essentially Precambrian terrane. It is suggested that the rocks underlying the Ignacio in the Animas Valley are not intrusive into the Ignacio formation.

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