CYCLIC SEDIMENTATION IN THE PRIDE SHALE: IMPLICATIONS FOR APPALACHIAN BASIN GEOMETRY AND ITCZ MIGRATION IN THE LATE PALEOZOIC

Spectral and geochemical analyses of an unusually thick succession of tidal rhythmites within the Pride Shale constrain the migration and intensity of the Intertropical Convergence Zone (ITCZ) during the Mississippian. It is hypothesized that a funnel-like basin geometry during deposition amplified the tidal signature in marginal marine environments and produced a strong tidal signature in the Pride Shale. Observations of modern, seasonal movement of the ITCZ and paleogeographic reconstructions, that place the Appalachian Basin in a near equatorial location in the late Paleozoic, suggest that the Pride Shale was deposited under the influence of the ITCZ. This creates the opportunity to test the assumption that due to stability of Hadley cell circulation, the distribution and movement of ancient climate belts was similar to that of the modern climate system. Variation in the amount of detrital influx recorded within seasonal cycles of the rhythmite succession provides a means of determining whether the ITCZ operated in the same manner in the past as it does today. Spectral analysis of the rhythmite successions is used to identify annual cycles and calculate the sedimentation rate. Variation in the intensity of the ITCZ is constrained by differences in the magnitude of fluxes of titanium and aluminum. Comparison of the magnitude of these fluxes to those of the modern Cariaco Basin is used to calibrate the fluxes with intensity of precipitation. Variation in the lateral extent of seasonal migration of the ITCZ is tested by examining the duration of the reoccurrence interval of seasonal, peak detrital influx. This work provides a means of testing the validity of assumptions of the character of Hadley Cell Circulation that are often incorporated within models of ancient and future climates.