ABSTRACT

Shelf edge, foreslope, and slope facies in the Lower to Middle Cambrian Shady Dolomite (600-1300 m thick) are exposed southeast of Austinville, southwestern Virginia, Valley and Ridge Province of the Appalachians. The Shady-Rome beds constitute an important type of Lower Paleozoic platform margin. The upward-shallowing platform sequence consists of shallow subtidal ribbon-laminated carbonates (Patterson Member) overlain by shoal water to tidal flat massive dolomites and fenestral cryptalgal carbonates (Austinville and Ivanhoe Members) that pass up into red mudcracked clastic and carbonate rocks (Rome Formation). The platform-margin is characterized by 1) shelf edge Epiphyton boundstone reefs, grainstone/packstones and rudites; these pass seaward into 2) thick sequences of fores ope, bedded limeclast packstone/grainstone, minor interbedded breccias and thin, black, shaly limestones; downslope these grade into 3) thin bedded, black, shaly limestone sequences that contain grainstone/packstone beds, downslope bioherms and blocks of Epiphyton boundstone and polymictic and oligomictic breccias composed of platform, foreslope and slope derived detritus; further seaward, these pass into 4) slope deposits that lack bioherms and are dominated by black shaly limestones, thin grainstone/packstones and oligomictic breccias containing slope-derived black shaly limestone clasts.

The southeastern Shady Dolomite facies are important in that they provide information on the character of the Cambrian carbonate platform margin in eastern North America. Further, the presence of blocks and bioherms of Epiphyton boundstone in the deeper-water, Shady breccias suggests that other deeper-water breccias in the Appalachians might also contain similar in-place or allochthonous Epiphyton reef limestones. The similarity of some of the slope lithofacies to relict features of metamorphosed carbonates in the southern Appalachian Piedmont, suggests that the Valley and Ridge rocks might provide useful information on protoliths and depositional processes for rocks in the Appalachian-Piedmont province.