CONODONT DISTRIBUTION PATTERNS AS A TOOL FOR IDENTIFICATION AND CHARACTERIZATION OF STRATIGRAPHIC SURFACES WITHIN PALEOZOIC SEQUENCES OF THE MIDCONTINENT, U.S.A

The application of sequence stratigraphic principles to Paleozoic strata within the Midcontinent is challenging. Low rates of subsidence and geologic settings unfavorable to stratigraphic completeness result in interpreted depositional sequences that are abbreviated with missing systems tracts and amalgamated bounding surfaces. These surfaces, however, can be subtle and difficult to identify in spite of their temporal significance. Conodont distribution patterns can be used as a tool to assist bounding surface identification and to aid in characterization of basinal trends of key surfaces and horizons within marine Paleozoic sequences. To explore this technique, bulk samples were collected and processed from beds of sections of the Iola Sequence (Upper Pennsylvanian) of eastern Kansas.

Temporal trends in conodont distribution were examined in samples from correlative sections of the Iola sequence. An abrupt increase in conodont elements/kg and an increase in species diversity characterize the interval directly above all bounding surface types within the Iola. Conodont elements/kg values are much higher, however, in the intervals above the maximum flooding surface or horizon and directly above the sequence boundary, than in the interval above parasequence boundaries. A change in taxonomic composition of samples above bounding surfaces also distinguishes sequence boundaries and maximum flooding surfaces or horizons from parasequence boundaries.

Spatial trends in conodont distribution were examined in samples above flooding surfaces in the Iola. Multivariate statistical analyses of conodont distribution suggest a correlation between sample composition and the relative location of the surface within the basin (updip versus downdip). The delineation of this type of stratigraphic gradient may have implications for the ability to predict updip versus downdip areas in regions with limited stratigraphic information and as such allow the construction of a preliminary sequence stratigraphic framework in these frontier regions. Also, conodont distribution patterns will assist in the identification of bounding surfaces in strata from areas with complex geologic settings or limited lateral extent.