Paper No. 37-8
Presentation Time: 9:00 AM-5:30 PM
GEOLOGY OF HORSESHOE BEND NATIONAL MILITARY PARK
The Battle of Horseshoe Bend, March 27, 1814, was a decisive American victory that effectually ended the Creek Indian War. Horseshoe Bend National Military Park, eastern Alabama, preserves this history and we report how Appalachian structures and lithologic sequences underlying the Park played a role in framing the battle. Bedrock and surficial 1:24K geologic mapping, petrographic thin section analysis, statistical geometric and kinematic structural analyses, and Ar-Ar mineral cooling studies are reported. In the Park, the NE-striking Jacksons Gap Group (JGG) defines the Brevard zone, which is a fundamental Appalachian fault zone extending into North Carolina. Deep, near sub-tropical weathering has caused the higher-grade and more thoroughly re-crystallized eastern Blue Ridge (EBR) and Inner Piedmont terranes that sandwich the JGG (NW and SE, respectively) to stand up in relief. The course of the Tallapoosa River was captured by the JGG valley along the southeast side of the infamous horseshoe-shaped bend. The river incised across strike of the Abanda fault, which borders the JGG/EBR, as it flowed westward to form the horseshoe-shaped bend. Erosionally weaker schist units in the EBR give way westward to more resistant tabular Late-Ordovician granite intrusions (Kowaliga Gneiss). The river anastomoses through these interleaved granites and schist producing many elongate islands before reestablishing a strike-parallel course that defines the northwest side of the horseshoe; farther west the river’s course is a meandering one. Thus, structural and lithologic control of the river’s course created the “horseshoe” peninsula used so brilliantly by General Andrew Jackson to cut-off and corner the Creek Indians and defeat them. New information gathered also indicates the Abanda fault has both right-slip and normal-slip movement histories, the latter implying late-orogenic collapse or Mesozoic rifting related to the opening of the Gulf of Mexico.