GEOLOGIC MAP OF THE 7.5 MINUTE MILLTOWN, ALABAMA, QUADRANGLE

The 7.5’ Milltown, Alabama quadrangle is located approximately 30 miles north of Auburn, Alabama. The eastern part of the study area is underlain by a recently discovered Ordovician (Taconian) arc terrane, the Dadeville Complex (DC), part of the Inner Piedmont. The north-west corner is underlain by metaturbidites of the eastern Blue Ridge (EBR), interpreted as slope/rise deposits along the ancient Laurentian margin. In the study area, the Brevard fault zone (BZ) has emplaced the DC upon the EBR and it is lithologically defined by metasiliciclastics of uncertain affinity called the Jacksons Gap Group (JGG). The ArcGIS geologic map was produced as part of the primary author’s master’s thesis. Field mapping was done to refine previous large-scale reconnaissance maps and to better constrain and understand the tectonostratigraphic relationships between the upper-amphibolite EBR, the upper-greenschist/lower-amphibolite JGG, and the complexly interfingered upper-amphibolite DC. We report the discovery of the Penton synform (PS). In the area of the quad, the PS is a large wavelength (~10 km half-wavelength) medium amplitude (~3 km) fold that trends N70^oE and plunges 28^oS. The PS only affects rocks of the DC, where it is defined by the folded metamorphic foliation and coplanar compositional layering; the adjacent JGG appears unaffected, following the characteristic N55^oE trend of the BZ.