TWO SOUTHERN APPALACHIAN PIEDMONT PALEOZOIC UNCONFORMITIES AND THEIR SIGNIFICANCE

An angular unconformity separates the fossil-bearing Middle Cambrian Asbill Pond Fm from the underlying Emory Fm in central SC. The contact between epiclastic rocks of the Emory Fm and the underlying Persimmon Fork Fm is gradational. Several studies have indicated that andesitic rocks of the PF Fm were erupted ca 550 Ma. Thus an orogenic event at the Cambrian-Precambrian boundary is indicated. Whether this is the same event recorded by rocks of the Charlotte t, and/or records the collision of Carolina slate and Charlotte t's as suggested by the Newberry eclogite has yet to be demonstrated. The Asbill Pond Fm exotic fauna does indicate that the event occurred on the periphery of Gondwana and is unrelated to accretion of composite Carolina to Laurentia. The unconformity was folded prior to the intrusion of the Clouds Creek Complex ca. 415 Ma. Structural trends related to this folding are truncated by the Stony Hill/Chappells sz on the southern margin of the Newberry eclogite.

A nonconformity separates the eastern Inner Piedmont (Cat Square t) from rocks of the western IP (Tugaloo t). This unconformity is locally reactivated as the Brindle Creek fault (Giorgis, 1999). Rocks of the Cat Square t contain detrital zircons as young as 430 Ma and include a population of ≤ 600 Ma zircons derived from Carolina (Bream et al, 2004). No plutons > 415 Ma intrude the Cat Square t. The BCf does not juxtapose rocks of different meta grade, and peak meta conditions occurred ca. 360 Ma on either side of the contact. Thus it is unlikely that the primary character of this feature is a thrust fault. Where the unconf has been observed in SC, significant retrogression (biot repl. gnt) is noted. No shear fabric is apparent in these coarse schists. These rocks yield monazite SHRIMP and TIMS ages in the range 330-320 Ma, and are interpreted to represent the passage of hydrothermal fluids along the unconformity during emplacement of the composite Piedmont thrust sheet. When the Inner Piedmont is restored to its Wenlock-Ludlow position it is clear that the Cat Square basin represents the southernmost extension of the classic New England and Maritime Salinic basins including CVS-Gaspé, Merrimack, Central Maine, Fredericton and LaPoile, and similarly records transtensional terrane dispersal following accretion of Carolina, coeval with a two stage rifting event recorded by plutonic rocks in the Carolina Piedmont.