Astronomical Tuning of Integrated Upper Famennian-Early Carboniferous Faunal, Carbon Isotope and High Resolution Magnetic Susceptibility Records: Western Illinois Basin

A complete marine sedimentary record spanning the late Frasnian and Famennian stages and early Tournasian is preserved and was sampled from long cores from southeastern Iowa. Preliminary results of biostratigraphic, paleomagnetic, and isotopic study of the Upper Famennian and Early Carboniferous interval in the H-32 core are presented. Units sampled in the H-32 core include the upper Saverton Shale, Maple Mill Shale, English River Formation, Louisiana Limestone, and lowermost Prospect Hill Formation. A continuous 87 foot long half split of the H-32 core was sampled at one foot or less intervals for conodonts; megafauna wherever encountered; at every one foot for whole rock inorganic C13 and trace element geochemistry, and at 5 cm intervals for whole rock magnetic susceptibility (MS). Conodont data support correlation of the H-32 core with the Upper postera (upper Saverton) to Upper praesulcata zones (Louisiana) spanning the upper Upper Famennian and entire Uppermost Famennian substages, and lowest Tournasian (uppermost Louisiana? and Prospect Hill). Inorganic dC13 data record 11 significant carbon isotope excursions showing progressively higher positive values of +1/mil in the upper Saverton, +2/mil in the Maple Mill Shale, excursions ranging from +3.5 to +4/mil in the English River, and maximum observed values from +6 to +7/mil in the Louisiana Limestone (interglacial Hangenberg Carbon Excursion). Fourier Transform analysis of MS data identify two significant peaks (at 41st harmonic and 243rd harmonic). We assign the 41st harmonic a value of 100,000 years as E2, then the 243rd harmonic is P1 of 16,872 yrs, recalculated from Berger for 360 Ma = 16,970 yrs. for P1. A strong peak represented by the 123rd harmonic appears to represent a value of 33,333 for O1 obliquity. The calculated astronomical duration of the integrated data set is 4.1 million years.