PENNSYLVANIAN CONODONT BIOSTRATIGRAPHY OF THE PARADOX BASIN

Idiognathodus- Neognathodus- and Streptognathodus-dominated conodont faunas occur in 19 of 53 fifth-order parasequences (depositional cycles) that comprise the upper Paradox and Honaker Trail Formations at Honaker Trail, Utah. Conodont elements are moderately common in maximum trangressive facies, but are rare to absent in intervening, and relatively thicker, shallow marine and non-marine beds. This patchy stratigraphic distribution, controlled principally by glacio-eustatic cyclicity, precludes subdivision of the section into contiguous range zones whose boundaries are based upon the “evolutionary” first occurrences of new species. Instead, conodonts are used as biotic signatures to distinguish individual parasequences or parasequence sets from others in a vertical succession. This sequence biostratigraphic approach 1) permits fingerprinting of selected Paradox basin cycles and 2) provides a means of matching Paradox basin cycles to their Midcontinent equivalents. Missourian conodont species (Idiognathodus eccentricus, I. sulciferus, and I. sp. A of Barrick et al.) first occur 56 meters above the base of the Honaker Trail Formation. Conocont occurrences in selected horizons of the Hermosa Group in Colorado, permits correlation of key horizons from the Southwest Shelf to the mixed carbonate-siliciclast sections on the Northeast Shelf near Durango, Colorado.