Paper No. 2
Presentation Time: 1:50 PM
DEVELOPMENT OF AN EPEIRIC SUBTROPICAL PALEOCLIMATE RECORD FROM WESTERN EURAMERICA: LATE FRASNIAN-EARLIEST TOURNASIAN STABLE CARBON ISOTOPE RECORD FROM THE YELLOW SPRING-NEW ALBANY GROUPS OF THE NORTHWESTERN ILLINOIS BASIN
Sampling of a series of Iowa Geological Survey (IGS) cores was initated in 2006 to develop a single continuous biostratigraphic sequence stratigraphic, and chemostratigraphic record spanning the Middle Givetian to Early Tournasian for the subtropical ocean of western Euramerica. Here initial results are presented from the first-round sample suite in the IGS Sullivan Quarry and H-32 cores from southeastern Iowa that provide a near continuous record through the Upper Frasnian, entire Famennian, across the Devonian-Carboniferous (D-C) boundary interval in the northwestern margin of the Illinois Basin. Whole-rock geochemical samples were taken at mid-point positions within conodont sample intervals permitting calibration with the Upper Devonian conodont zonation in the IGS Sullivan Core. Large sample spacing (> 30 cm) in the lower part of the Sullivan core did not capture clear records of the Kellwasser excursions as documented in the Devonian composite records of Buggisch, and Joachimski and others. Numerous (>20) excursions are evident in the Famennian interval spanning the Middle triangularis through Middle exspansa zones. δ13Ccarb values within this long interval fall below maximum values of +0.3‰ and minimum values of -4.0 ‰, with certain excursions displaying maximum changes of δ13Ccarb values of up to 2‰. Positive δ13Ccarb values (up to +0.3‰) characterize the prolonged excursion within the interval of Middle-Upper triangularis Zone, that drop below +0.0‰ for the remainder of the Famennian through the interval of the Middle expansa Zone. Significant positive δ13Ccarb excursions commence in within the Upper expansa-Lower praesulcata? zones where an initial positive excursion reaches values of +2.0 ‰, succeeded by the onset of the Hangenberg Excursion signified by two initial excursions with peak values of +4.0 ‰ and +3.9‰ within the Middle praesulcata Zone. Values within the Upper praesulcata Zone are above +5.0 ‰ peaking at >+6.0 ‰ within the Louisiana Limestone carbonate platform. Louisiana Limestone platform deposition was terminated by a major sea level low-stand likely associated with onset of early Tournasian glaciation. Early Tournasian values are still at or above +4.0 ‰ in the Prospect Hill Formation.