"REALLY, HOW OLD ARE YOU?" THE ENIGMA OF THE AGE AND BIOSTRATIGRAPHIC CORRELATIONS OF THE NEW PROVIDENCE SHALE (LOWER CARBONIFEROUS; OSAGEAN) AND ITS RELATIONS TO THE REMAINDER OF THE LOWER MISSISSIPPIAN CLASTIC SUCCESSION OF SOUTHEASTERN INDIANA, USA

The Lower Mississippian Borden Delta is a classic example of a time-transgressive, siliciclastic, basin-filling succession in an otherwise carbonate-dominated region. In Indiana, the Borden Delta was deposited on the northeastern fringe of the Illinois Basin, which was undergoing its most rapid subsidence since its formation.

The basal deposit of the Borden Delta in Indiana is the New Providence Shale, which represents the basinal pro-delta environment. The New Providence is composed of greenish to grayish clay shales, which can be locally very fossiliferous. The entire Lower Mississippian clastic succession of southeastern Indiana (New Providence Shale, Kenwood Siltstone, Spickert Knob Fm., Floyds Knob Bed, and Edwardsville Fm.) includes two 3rd order sequences. The New Providence Shale represents the transgresive systems tract of the New Providence Sequence deposited during the sea-level rise during the early Visean.

The age of the New Providence Shale has been debated since its original description by Borden (1974). Springer (1911), Conkin (1957), Rexroad and Scott (1964), and Kammer (1985) have proposed different ages for the New Providence Shale, ranging from the equivalentof the Fern Glen to the early Keokuk (middle Tournaisian to early Visean), using crinoids, brachiopods, and conodonts. Location of the Tournaisian-Visean boundary in this region should help define the exact age of the New Providence Shale. The first occurrence of Lycospora pusilla defines the base of the Visean (Pu Biozone) in Europe. In the study area, the palyno-assemblage of the New Providence Shale is not correlative with the western European Zones, and Lycospora pusilla does not appear until higher in the succession (Floyds Knob Bed). The reasons for these age discrepancies between faunal and floral groups could result from changes ranging from sedimentologic processes to plant paleoecology.