Early Devonian Conodont-Graptolite Collation and Correlations with Brachiopod and Coral Zones, Central Nevada

Abstract

A range chart of some Early Devonian conodont and graptolite taxa from central Nevada is presented. It is based on the graphic correlation method of Shaw, and shows correlations with the established zones for brachiopods and corals as well as conodonts and graptolites. It indicates that the hesperius through pesavis conodont zones established for western North America are approximately equivalent to the Lochkovian of the Czechoslovakian sequence, and the Pragian begins approximately with the sulcatus zone. The chart also indicates that the zones based on different groups do not coincide, are of very unequal duration, and that intervals of rapid morphologic change correspond to intervals of higher diversity and greater morphologic variation. Species have significantly diff rent longevities, generally those originating during times of greatest morphologic variation being the shorter lived. The approximate duration of the species studied is 2 to 10 m.y. Use of the graphic correlation method permits better correlation of shelf and basin faunas and enhances the possibility for constructing accurate shelf margin histories and for correlating provincial shelf faunas with those in other parts of the world.