2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 24
Presentation Time: 8:00 AM-12:00 PM


BLACKSTOCK, Joshua M., Department of Earth Sciences, U. of Arkansas – Little Rock, 2801 South University Avenue, Little Rock, AR 72204-1099, BOSS, Stephen K., Dept. of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701 and LESLIE, Stephen A., Department of Earth Sciences, University of Arkansas at Little Rock, Little Rock, AR 72204, jmblackstock@ualr.edu

Reconnaissance of the Clifty Formation (Devonian) in northwest Arkansas revealed sedimentological features and trace fossil assemblages indicative of shallow marine through subaerial coastal environments. Throughout the study area, the Clifty Formation is an orthoquartzite. Sedimentological features of the Clifty Formation include massive-bedded deposits, thick (0.5-m) tabular beds, planar-tabular cross-beds, relatively large (ca. 15 m wide x 7m deep) channel deposits, thin tabular beds, festoon cross-bedded sandstone monoliths (up to 10-m high), small (<3-m wide x <2-m deep) trough cross-bedded channel deposits, and massive non-bedded, poorly-cemented sandstone pods. Massive bedded deposits include abundant horizontal tracks and trails indicative of a subtidal, shallow shelf environment. Thick tabular beds also include abundant horizontal tracks and trails along with Zoophycos (?), indicative of slightly deeper subtidal or deep marine lagoon environments. Planar-tabular cross-bedded deposits contain vertical traces similar to those made by anemones and large (up to 1-m diameter) circular structures of unknown biological affinity. Nearby, outcrops expose sizeable channels containing vertical burrows (possibly anemones). Planar-tabular cross-bedded deposits and nearby channels are interpreted as deposits of a shallow, tide-dominated shelf setting. Thin tabular layers (<0.3-m thick) are associated with Skolithos and are interpreted as intertidal (beach) deposits. Isolated festoon cross-bedded sandstone monoliths lack biological traces and are interpreted as subaerial coastal dunes. Dunes are separated by trough cross-bedded, bioturbated deposits interpreted as inter-dune runnels. Massive, poorly-cemented sandstone pods have traditionally been interpreted as infilling paleo-sinkholes developed in underlying Ordovician carbonate units. Future study of the Clifty Formation will help define the geographic extent of facies for a paleoenvironmental map of this unit.