Russell R. Kelly1, Gregory C. Nadon1
(1) Ohio University, Athens, OH
ABSTRACT: Lateral Variability within High Frequency Sequences in a Distal Foreland Basin Setting
Recent investigations have shown that the high frequency sequences in Pennsylvanian strata contain numerous, crosscutting unconformities that call into question intra- and interbasinal correlation of marine bands. Correlation is particularly problematic in low accommodation settings such as the distal foreland of the Appalachian basin. The interval that contains the most widespread marine marker bed within the Conemaugh Group, the Ames Limestone, was chosen to determine over what length scale different facies within a single sequence can be correlated.
Measured sections throughout a 400 km2 study area have identified at least two sequences within the Ames interval. Ideally, the sequences are bounded above and below by paleosols. Lithologies of the basal sequence vary from coal to black fissile shale to gray laminated mudstones. The facies marking the middle sequence boundary vary from a paleosol to a shoreface sandstone. The upper sequence contains coals, laminated mudstones and marine limestones. The limestones are overlain by laminated mudstones that, in some cases, grade into a paleosol. Locally, fluvial incision of the late highstand (HST) and lowstand (LST) has removed some or all of the upper sequence.
Lateral continuity of the facies is most pronounced in sediments of the Transgressive Systems Tract (TST). Facies in the TST are continuous over 10's of kilometers and appear to be restricted mainly by paleotopography. Variable incision of the late HST to LST by fluvial channels creates abrupt lateral facies changes over less than 20 meters in each HST facies.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado