Late Tertiary tectonic uplift in the southern and central Appalachians

• Main Author: Biswal, Mary Sheela
• Format: Text
• Language: unknown
• Published: TRACE: Tennessee Research and Creative Exchange 2015
• Subjects: Tertiary; Uplift; Appalachians; Zircons; Terraces; Geology; Alabama; Broad River; Newfoundland
• Online Access: https://trace.tennessee.edu/utk_gradthes/3563; https://trace.tennessee.edu/cgi/viewcontent.cgi?article=4889&context=utk_gradthes

The exposed Appalachian Mountains extend about 2500 km from Newfoundland to Alabama with the highest peaks >2000 m above sea level. The last orogeny that affected Appalachian crust was the 325-260 Ma Alleghanian. Even with minimal erosion rates, it is highly unlikely that the Appalachians could have sustained such elevations for over 200 m.y., suggesting that recent tectonic uplift has produced today’s mountainous topography. The multiple phases of Tertiary uplift are related to poorly understood processes, but a large amount of data from today’s mountain chain and the adjacent Coastal Plain indicate the present high topography is anomalous and clearly not related to Paleozoic crustal processes. Uplift signatures suggest that current topography and visible geomorphology are a product of the late Tertiary uplift. Antecedent rivers flowing westward across very high topography in the Blue Ridge, westward-migrating drainage divide and anomalous drainage patterns are common in the southeastern Appalachians. A marked shift in high topography occurs northward from the Blue Ridge in Tennessee-North Carolina to the Valley and Ridge in Virginia-West Virginia. Evidence suggests a possible late Tertiary tectonic uplift in the southern and central Appalachians, although more data and evidence are needed to understand the uplift. The main research problem of this project is to identify and analyze uplift signatures as recorded in lower Gulf Coastal Plain sediments and fluvial terraces along Douglas Lake, French Broad River. Detrital zircon geochronology of Miocene-Pliocene lower Gulf Coastal Plain sediments shows important age peaks at 1.0 Ga, 600 Ma, 480 Ma, 440 Ma and 300 Ma. Collective zircon data suggest a possible predominance of Appalachian provenance. This indicates occurrence of tectonic uplift in the source region during the Miocene-Pliocene, producing exceptionally high sediment influx in the Coastal Plain during that time. Fluvial terrace mapping along Douglas Lake, Tennessee has been done with the help of vintage topographic maps and classic geologic mapping involving foot traverses. A provisional geologic terrace map at 1:24,000 scale has been produced as part of this study. Terrace mapping has helped identify five distinct terraces, resolve their relative chronology and understand the evolution of terraces along the river.