Book Synopsis The Middle Ordovician Tellico-Sevier Syncline by :
Download or read book The Middle Ordovician Tellico-Sevier Syncline written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Analyses of remote-sensing satellite data, aerial photography, radar images, and digital elevation models, and detailed (1:24,000-scale) geologic mapping of bedrock and surficial deposits were conducted in a portion of the southeastern Tennessee. This area contains the southern portion of the Tellico-Sevier Alleghanian syncline and the highest concentration of modern earthquakes as well as two major rivers with unconsolidated floodplain and terrace deposits that would be most susceptible to disruption by earthquakes. Cambrian to Mississippian age rocks occurs in the syncline. The majority of detailed mapping was conducted in Middle Ordovician Chickamauga Group rocks. Earthquakes occur in the East Tennessee seismic zone (ETSZ) with greater frequency than anywhere east of the Rocky Mountains outside of the New Madrid seismic zone and the Charlevoix region in Canada. No earthquakes greater than M = 4.9 have been recorded in the ETSZ, although the observation window of historical seismic activity is narrow. It is possible that large earthquakes have occurred in the past. The identification of two sites in or near the modern ETSZ with anomalous and potentially earthquake-related deformed Quaternary sediments underscores the need for continued study to properly assess the seismic hazard of this zone. Bedrock and surficial geologic mapping did not produce unequivocal evidence of earthquake-related neotectonic deformation. The geologic map constructed between the Little Tennessee and Tellico Rivers does, however, reveal several previously undocumented stratigraphic and structural geometries. A new stratigraphic column has been developed for the southern portion of the Tellico-Sevier syncline in sufficient detail to separate potential Quaternary paleoseimic features from both Alleghanian deformation and depositional-related features such as paleosinkholes or facies changes. The stratigraphic column also unifies the previously terminology for Paleozoic units. This column uses established rock unit names that, although they do not conform to current state geologic map terminology, more accurately represent the rocks present in the southern portion of the Tellico-Sevier syncline. The Chapman Ridge Sandstone was studied in particular detail. It has never been mapped as a discrete unit over such a large area; so only a few 1:24,000-scale geologic maps separate it from the Holston Formation. Facies and unit thicknesses in the Chapman Ridge vary across and along its outcrop belt. It is less cross bedded, less ferruginous, and thinner to the south. The Chapman Ridge is thinner in the southeastern limb and thicker in northwestern limb of the Tellico-Sevier syncline. Cross-bed orientation measurements were collected at over 50 stations between Tennga, Georgia, and Mascot, Tennessee, to determine paleocurrent vectors to investigate paleodispersal. These data reflect a weak though discernable pattern of regional current directions (south-southeast) and sediment dispersal. The Tellico-Sevier syncline formed during Alleghanian deformation in the hangingwall of the Chestuee/Dumplin Valley thrust sheet. Interpretation of seismic reflection data and forward modeling suggest the northwest limb of the future syncline was later modified by out of sequence duplexing in the underlying Saltville sheet, creating the southeastern limb. Continued movement of the Blue Ridge thrust sheet further deformed the southeastern limb of the syncline. Shortening attributable to the Chestuee and Dumplin Valley faults, folding, and faulting in the syncline may be [approx.] 42 km. Backthrusting in the southern limb of the Kyker Bottoms folds thins the Athens shale. Generation of the Belltown folds near Tellico Plains, Tennessee and associated faults are more complex than was originally thought, and may point to a relationship with faulting further southwest.
