PRELIMINARY RESULTS OF HIGH-RESOLUTION INVESTIGATION OF UPPER DEVONIAN (LATE FRASNIAN-FAMENNIAN) RELATIVE SEA LEVEL AND CLIMATE RECORD FROM THE SUBSURFACE OF THE IOWA AND WESTERN ILLINOIS BASINS

A complete thermally pristine organic-rich hemipelagic and outer shelf clastic and carbonate succession provide a major reference section for the Upper Devonian and Devonian-Carboniferous boundary in the western Illinois Basin in southeastern Iowa. Preliminary results of sequence stratigraphic, conodont-biostratigraphic, paleomagnetic, and isotopic study of the Upper Devonian and D-C boundary interval in the Sullivan and H-32 cores are presented. Units sampled in the IGS-Sullivan H-32 cores include the Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, Maple Mill Shale, English River Formation, Louisiana Limestone, and lowermost Prospect Hill Formation. In the Sullivan Core, the Sweetland Creek Shale and lower Grassy Creek Shale were deposited during parts of two late Frasnian 3rd order sequences coinciding with Devonian Transgressive-Regressive cycle IId of Johnson and others, and span part of Montange Noire Zone 12, and all of Zone 13. Above the Frasnian-Famennian boundary, three major third order sequences comprised of cyclic successions of organic rich brown shales and overlying burrowed grey fossiliferous shales of the Grassy Creek and Saverton formations were deposited during Devonian T-R cycle IIe of Johnson and others. Outer shelf shales of Maple Mill and overlying middle shelf siltstones and mudstones of the English River comprise a Late Famennian 3rd order sequence, and the overlying Louisiana Limestone represents a Latest Famennian carbonate platform succession deposited during the very late Famennian eustatic sea level rise and highstand. Louisiana carbonate platform deposition in Iowa and Missouri was terminated by a major sea level low-stand likely associated with onset of early Tournasian glaciation. High resolution inorganic δ13C carb and high resolution magnetic susceptibility data provide evidence for the shift from global greenhouse to icehouse climate coincident the first interglacial sea level rise that initiated Maple Mill and English River deposition in the Upper Famennian, and the most complete record known of the Hangenberg Carbon Excursion during the interval of Devonian T-R cycle If of Johnson and others.