Abstract
Depocenters in the southern and central Appalachians in Virginia appear to have been a major influence on thickness and carbonate facies distribution on the passive Cambrian-Ordovician shelf and in the Middle Ordovician foreland basin. The Upper Cambrian Nolichucky Formation illustrates sedimentation patterns associated with a shelf embayment (located above the southern Appalachian depocenter) on the passive Cambrian shelf. The Noli-chucky Formation is an onlap-offlap, shallow ramp to deep shelf sequence that consists of peritidal stromatolitic carbonate rocks, ooid grainstones, deeper ramp ribbon carbonate rocks, and embayment plain shale/siltstone/flat-pebble conglomerate facies. Facies bands are normal to the regional shelf edge and parallel the outline of the shelf embayment. The Middle Ordovician sequence illustrates the influence of depocenters on foreland basin evolution during a time of profound tectonism, when the shelf edge was uplifted, deformed, and subjected to erosion. The Middle Ordovician ramp-to-basin sequence is an onlap-of-flap package, that consists of peritidal fenestral lime mudstones, shallow subtidal cherty wackestones, ramp and downslope skeletal buildups, deeper ramp shaly skeletal wackestones, and basinal black limestones and shales. Widespread ramp and basin deposition commenced in southwest Virginia during south to north transgression from the southern depocenter. Widespread downwarping extended the basin into northern Virginia. Rapid clastic influx coupled with progradation of the carbonate ramp caused the southern basin to fill. Recognition of depocenters associated with carbonate sequences in orogenic belts is important if controls on direction of transgression, facies distributions, and thicknesses of units are to be better understood. Furthermore, the carbonate depocenters appear to localize development of subsequent clastic wedges. End_of_Article - Last_Page 770------------
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