CORRELATING AND CHARACTERIZING SMALL-SCALE FLOODING SURFACES WITHIN A HIGH-FREQUENCY SEQUENCE USING CONODONT DISTRIBUTION PATTERNS: IOLA LIMESTONE (UPPER PENNSYLVANIAN), MIDCONTINENT USA

Temporal and spatial distribution patterns of conodonts have been examined relative to stratigraphically significant surfaces within the Iola Limestone in Kansas and Iowa, and these patterns are being used to characterize and assist in the correlation of these surfaces. Previous studies have documented more stratigraphic complexity within the Iola Limestone than accounted for using the cyclothem model. The Iola Limestone has been described as a major cyclothem or Kansas Cyclothem, representing lithofacies deposited during one major transgression and regression. This major cyclothem has been characterized by the vertical succession of specific lithofacies. Correlation of the Iola relative to temporal and spatial stratal trends reveal as many as two unconformity-bound HFS's (high-frequency sequences), both of which consist of a number of smaller-scale cycles (parasequences). The Raytown HFS (upper) in the Iola contains as many as 2 parasequences. Correlation of the marine flooding surface that bounds the uppermost parasequence in the Raytown (although somewhat problematic) reveals some interesting patterns that are somewhat contrary to the trends predicted for the regional model for major cyclothems.

Conodont samples were collected directly above, and from strata both above and below the basal bounding surface of the uppermost parasequence in the Raytown HSF. This parasequence boundary can be correlated with some confidence along the outcrop belt for the Iola in Kansas where it is characterized by a thin shell accumulation (lag?) marking the abrupt transition from massive phylloid algal carbonates to thinly-bedded argillaceous carbonates. The Raytown HFS in Iowa also consists of at least 2 parasequences, but the bounding surface of the uppermost parasequence has some different characteristics. This bounding surface is characterized by the abrupt change from thick-bedded cherty limestone to medium-grey fossiliferous shale. It appears that the facies directly above this surface in Iowa represent more offshore conditions than the facies directly above this bounding surface in Kansas. This is also supported by the taxonomic and taphonomic distribution patterns of conodonts. Sections of the Iola in Iowa were presumably further up on the platform towards shoreline than the sections of this formation in Kansas.