DEPOSITIONAL CYCLICITY INDICATED BY MAGNETIC SUSCEPTIBILITY IN THE NEW ALBANY SHALE FRASNIAN (UPPER DEVONIAN) STRATA IN THE ILLINOIS BASIN OF WESTERN KENTUCKY

Magnetic susceptibility (MS) is a proxy for the concentration of ferromagnetic minerals, which in sedimentary rocks vary in response to global climate and sea level change. Samples were collected from the New Albany Shale in western Kentucky, a unit of black to dark grey shale with pyrite nodules and rare carbonate beds that were deposited in an epicontinental sea which filled the Illinois Basin. The Upper Devonian is preserved within the New Albany Shale, including the Frasnian-Famennian (F-F) boundary which is recognized to a 5 cm interval based on conodonts. Fifteen major trends in magnetic susceptibility in the 55.78 meter section are most likely due to gradual shifts in sea level. Shorter duration shifts in MS within the major trends support records of precessional cyclicity. Microfossils and conodont zonation defined marker beds throughout the New Albany Shale provided controls in cross-basinal comparisons to Walnut Creek in New York and the Arbuckle Mountains in Oklahoma, as well as global correlation to the Montagne Noire of southern France. Two similar trends across the Frasnian-Famennian boundary at these locations support a global climate shift due to a fluctuation in sea level.