EXAMPLES OF MAP-SCALE F1 GENERATION FOLDING IN THE TALLADEGA BELT: OZAN AND SHELBY QUADRANGLES, AL

The Talladega Belt (TB) in Alabama represents the easternmost Laurentian continental margin terrane within the region and is composed of predominately metaclastic and metacarbonate units capped by metavolcanic rocks. The lowermost stratigraphy within the TB is the Kahatchee Mountain Group (KMG) that represents early Paleozoic drift facies deposited during opening of an ocean basin adjacent to Laurentia. The Talladega Group (TG) overlies the KMG along the regional Pre-Lay Dam Fm. Unconformity (PLDU), and represents a successor basin sequence related to mid-Paleozoic extension. Recent mapping research funded by the USGS EDMAP program has identified several map-scale syn-metamorphic asymmetric F1 folds that have been classified as F3 generation folds by previous mapping. Although the axial trace of the F1 folds aligns with F3 axial traces in the Columbiana Mountain area, this alignment is coincidental. Mapping transects across the map-scale F1 hinge zones have measured S1 axial planar cleavage dipping consistently to the southeast at moderate dip angles. However, bedding in F1 short limbs dips steeply the northwest, and bedding in the long limbs dips at moderate to low angles to the southeast but less steeply than S1 cleavage. Outcrop-scale parasitic F1 folds reverse these trends. The consistent pattern of bedding and cleavage geometry established by F1 folding is not significantly disrupted by later megascopic folds (mainly F3) in the study area. Megascopic F1 folds in the Ozan/Shelby area are recognized because of the distinctive "marker" units such as the Brewer Phyllite and metasandstone members in the Waxahatchee Slate. The KMG is regionally discontinuous along much of the TB strike length because of the structural level of the basal thrust, therefore, the geographically closest structurally equivalent megascopic F1 folds are exposed 150 km northeast along strike.