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Sedimentary History and Biostratigraphy of Late Silurian-Early Devonian of Southern Appalachians and Southeastern Craton

Thomas W. Broadhead, Deborah A. Capaccioli, Nancy E. Neff, Sarah R. Reid

The Late Silurian and Early Devonian sedimentary record of the southern Appalachians is preserved as a patchwork of shallow marine carbonate and terrigenous clastic rocks. These units commonly are bounded by unconformities, and biostratigraphic resolution has been lacking until recently. In Tennessee, the Sneedville formation (Hancock Dolomite of USGS usage) contains stromatoporoid faunas that correlate it with the Upper Silurian (Pridoli) Rondout (New York) and Tonoloway (central Appalachians) Formations, but recent conodont discoveries suggest a lower age limit in the Ludlow (crispa zone). Sneedville carbonates and clastics represent a broad range of shallow subtidal and peritidal facies that underwent periodic deepening and shoaling.

In Georgia, correlative rocks are absent, and the Red Mountain Formation (Lower Silurian, Llandovery) is locally overlain by upper Lower Devonian Armuchee Chert-Frog Mountain Sandstone or by uppermost Devonian Chattanooga Shale. Reevaluation of the Red Mountain-Frog Mountain interval in Alabama showed a brachiopod fauna that correlated to the Keyser Limestone (uppermost Silurian-lowermost Devonian) of the central Appalachians.

Cratonward, a relatively complete succession of Upper Silurian-Lower Devonian carbonate rocks in west-central Tennessee (Decatur Limestone, Ross Formation) contrasts with the hiatus-bounded sections of the Appalachians. Toward the south, the Decatur intertongues with the lower Ross (eosteinhornensis zone), but to the north, the upper Decatur and Ross are both Devonian (woschmidti zone). The Decatur-Ross interval correlates with the Hunton Group of Oklahoma and is an ecologic analog and part temporal equivalent of parts of the Helderberg Group of New York.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.