GEOLOGIC MAP OF THE OAK LEVEL, ALABAMA, QUADRANGLE: DELINEATION OF THE PRE-LAY DAM UNCONFORMITY IN THE NORTHEASTERN-MOST TALLADEGA BELT

The Talladega Belt (TB) in Alabama represents the eastern-most Laurentian continental margin terrane within the region and is composed of metaclastic and metacarbonate units capped by the uppermost Hillabee Greenstone metavolcanics. The lowermost stratigraphy within the TB is the Kahatchee Mountain Group (KMG) that represents early Paleozoic drift facies deposited during opening of Iapetus. The Talladega Group (TG) overlies the KMG along the regional Pre-Lay Dam Unconformity (PLDU), and represents a successor basin sequence related to mid-Paleozoic back-arc extension. Recent mapping funded by the USGS EDMAP program has discovered units of the KMG and TG in the Oak Level 7.5' quadrangle near the Alabama-Georgia state boundary. The Brewer Phyllite formation, predominantly a Fe-rich phyllite containing distinctive chlorite porphyroblasts, has been mapped along regional strike across the quadrangle where the unit apparently is truncated by the Talladega-Cartersville thrust fault (TCF) to the northeast of the quadrangle. The Wash Creek slate stratigraphically overlies the Brewer Phyllite and is in turn unconformably overlain by the distinctive feldspathic blue-quartz metasandstone units of the Lay Dam formation thus delineating the PLDU. The PLDU persists along regional strike into the Georgia portion of the TB. Important conclusions to be drawn from the mapping project include: (1) the lateral continuity of the Brewer Phyllite marker horizon (> 150 km) along regional strike, (2) equivalent along-strike persistence of the PLDU, and (3) the significant stratigraphic thickening of the KMG and TG in the mapping area as the TCF cuts down-section in the hanging wall (TB).