Craig R. Cormany1, Gregory C. Nadon1
(1) Ohio University, Athens, OH
ABSTRACT: Amalgamation of Incised Channel and Incised Valley Fill Sandstones in Low Accommodation Zones
Incised Valley Fill (IVF) sandstone deposits are an attractive exploration target provided the geometry can be properly evaluated. The distal foreland of the Appalachian basin contains exposures of multistorey sandstone within the Conemaugh Group (Virgilian) that are in excess of 40 meters thick that has been interpreted as an IVF deposit. However, an equally plausible interpretation that has not been explored is that anomalously thick coarse-grained sandstones are an amalgamation of separate, smaller scale, incised channel events in a low accommodation setting.
Both scenarios could contain similar grain sizes and structures, but should have very different geometric configurations and associated paleosols. Paleosol intensities on adjacent interfluves should vary depending on sediment supply and duration of subaerial exposure. An IVF deposit should have a single, anomalously well-developed paleosol adjacent to the sandstone body. A succession of smaller, stacked incised channels would produce a series of composite paleosols at roughly equal stages of development.
The two hypotheses were evaluated with detailed sections, constructing isopach and isolith maps from one well-exposed sandstone over an area of 320 km2. Data indicates that both interpretations are partially correct. Basal and upper portions are composed of incised channel sandstones up to 10 m thick and less than 1 km wide. The middle lithesome, commonly referred to as the Connellsville Sandstone, is more laterally extensive (>6 km) and up to 20 m thick. Alternation between incised channel and IVF deposits suggests that sandstone geometry varied with the relative rate of creation in accommodation space.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado