Carboniferous Gnathodontid and Neognathodontid Conodont Taxa: Application to Understanding Unusual Platinum-Group Geochemistries

Robert C. Grayson Jr., Glen K. Merrill

Reconstruction of apparatuses of Carboniferous gnathodontid and neognathodontid conodont taxa provides a basis for revising their phylogeny. Within the two distinct clades, a number of genera and species have been recognized. Some revision of these now seems necessary. At the generic level, any taxonomic revision should reflect the new understanding of phylogenetic relationships. Utilizing a species concept that takes into consideration the mode of evolution within each clade results in an improved and more precise biostratigraphy. This biostratigraphic philosophy has been useful in interpreting the origin and significance of mudrocks that show unusual geochemistry similar to those that have been found in association with the K/T boundary.

Six stratigraphically different platinum-group enrichments have been discovered: four of these are within the Carboniferous succession of central Texas and southern Oklahoma, and two are within the Ordovician of southern Oklahoma. At present, our data for the mid-Carboniferous platinum-group enrichment is the most complete. Coincident conodont samples demonstrate that the enrichment mechanism was neither synchronous nor equal in its effects across the basin. We are as of now unsure of the exact cause of enrichment. Whatever the process may be, it is clearly associated with the accumulation of muddy sediments containing organic material, phosphate and glauconite. Our findings lead us to conclude that similar geochemistries at the K/T boundary should be reexamined for the possibility th t some or all of the iridium might be of sedimentary origin.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995