ABSTRACT The Appalachian Mountains expose one of the most-studied orogenic belts in the world. However, metamorphic pressure-temperature-time ( P-T-t ) paths for reconstructing the tectonic history are largely lacking for the southernmost end of the orogen. In this contribution, we describe select field locations in a rough transect across the orogen from Ducktown, Tennessee, to Goldville, Alabama. Metamorphic rocks from nine locations are described and analyzed in order to construct quantitative P-T-t paths, utilizing isochemical phase diagram sections and garnet Sm-Nd ages. P-T-t paths and garnet Sm-Nd ages for migmatitic garnet sillimanite schist document high-grade 460–411 Ma metamorphism extending south from Winding Stair Gap to Standing Indian in the Blue Ridge of North Carolina. In the Alabama Blue Ridge, Wedowee Group rocks were metamorphosed at biotite to staurolite zone, with only local areas of higher-temperature metamorphism. The Wedowee Group is flanked by higher-grade rocks of the Ashland Supergroup and Emuckfaw Group to the northwest and southeast, respectively. Garnet ages between ca. 357 and 319 Ma indicate that garnet growth was Neoacadian to early Alleghanian in the Blue Ridge of Alabama. The P-T-t paths for these rocks are compatible with crustal thickening during garnet growth.

ABSTRACT In a well-defined subrecess in the Appalachian thrust belt in northwestern Georgia, two distinct fold trains intersect at ~50° in the down-plunge depression of the Floyd synclinorium. A mushwad (ductile duplex) of tectonically thickened weak-layer rocks (primarily the shale-dominated Cambrian Conasauga Formation) filled the space beneath folds and faults of the overlying Cambrian–Ordovician regional stiff layer (mushwad roof). Measurements of the mushwad thickness from balanced cross sections provide the basis for three-dimensional (3-D) models. Tectonically thickened weak-layer shales in a model using a simple line-length balance of the stiff layer have a volume of ~64% of the volume in the deformed-state model, indicating that this balanced reconstruction is not appropriate. Previous work demonstrated deposition of a thick mud-dominated succession in a basement graben to balance the volume. A 3-D model incorporating a thick Conasauga Formation shale succession deposited in a basement graben yields good correspondence to the deformed-state mushwad volume. That model requires vertical separation on the graben boundary faults greater than the present small-magnitude separation; unconformable truncation of the upper part of the Cambrian–Ordovician carbonate succession documents Ordovician inversion of the graben boundary faults. In the 3-D models, the distribution of thickness in the deformed state suggests movement of weak-layer shale out of the planes of cross sections and up plunge away from the structural depression of the Floyd synclinorium. Out-of-plane tectonic translation is consistent with a relatively uniform depositional thickness of ~800 m, which allows calculation of the magnitude of vertical separation on basement faults during Conasauga Formation deposition.

Speleothems are valuable archives of climate change because of their extraordinary time resolution, which is unattainable in other terrestrial climate proxies. Analyses of 4796 ultraviolet fluorescent (UVf) layers observed in polished thin sections of a 15-cm-long speleothem collected from Raccoon Mountain Cave near Chattanooga, Tennessee, USA, as well as 200 δ 13 C and δ 18 O measurements and 11 high-precision U/Th dates permit refined interpretations of middle and late Holocene paleoclimate records in the southeastern United States. Speleothem UVf layers average 0.015 mm, identical to the average growth rate determined for the middle and late Holocene portions of the speleothem (ca. 7600–400 yr B.P.) based on the U/Th ages and interval thicknesses. UVf layer counts between paired U/Th ages are also consistent with determined ages and further support their interpretation as annual layers. The middle Holocene is typified by 100–400 yr intervals of higher rainfall characterized by thin UVf layers (0.003–0.010 mm) and more-negative δ 13 C values (−3‰ to −6‰ Peedee belemnite [PDB]), punctuated by shorter periods (5–20 yr, rarely 50–100 yr) of lower rainfall with thicker UVf layers (0.030–0.080 mm) and less-negative δ 13 C values (−1‰ to −3‰ PDB); “extreme drought” events are characterized by both the thickest UVf layers (0.150–0.170 mm) and the least-negative δ 13 C values (+0.05‰ to −1‰ PDB). The late Holocene, in comparison, is characterized by overall wetter conditions and more regular (sinusoidal curve) behavior, suggesting 50–100 yr cycles of higher and lower rainfall, with UVf layers ranging from 0.005 to 0.030 mm/yr. Statistical analyses of UVf layer thicknesses using order-two momentum threshold vector autoregressive models (MTVAR2) quantify the relationship between δ 13 C and δ 18 O, dependent upon the momentum in the climate. This study demonstrates that thickness of annual layers in speleothems can be used to resolve detailed paleorainfall records, provided there is preservation of organic matter sufficient to excite UVf response; however, relationships among changes in rainfall amounts, stable isotope values of speleothem calcite, and thicknesses of UVf annual layers (≈growth rates) are not straightforward.

Abstract Upper North Chickamauga Creek in Hamilton and Sequatchie Counties, Tennessee, is severely impacted by acid mine drainage (AMD) emanating from more than 15 abandoned coal mines in headwater tributaries. AMD is formed when pyrite and other sulfide minerals are exposed to air and water during coal mining. It is characterized by low pH (<2.8) and elevated concentrations of acidity, iron, aluminum, sulfate, and other pollutants. These attributes tend to be toxic to most aquatic life and result in reduced aesthetics and potential uses of the water. The North Chickamauga Creek Watershed Restoration Project is a multi-organizational effort to restore the upper 18 miles of the North Chickamauga Creek watershed to a level that will support a warm-water fishery. Several passive treatment systems (PTS) have been installed at abandoned mining sites in the North Chickamauga Creek watershed where AMD is generated and is flowing into surface waters. PTS is the engineered use of natural and enhanced geological, biological, chemical, and physical processes to prevent pollutant generation or to remove pollutants from aqueous discharges. PTS include technologies such as constructed wetlands, anoxic limestone drains, mine seals and flooding, successive alkalinity-producing systems, limestone trenches, and other components. During this field trip to the upper reaches of the North Chickamauga Creek watershed, we will visit several of the operational systems and observe untreated AMD. Participants will gain an understanding of how AMD is generated, its impacts and characteristics, and how it can be prevented or treated. This field trip requires extensive hiking over moderate slopes and sometimes vegetated terrain.

Abstract The linear Sequatchie anticline interrupts the continuity of the Appalachian Cumberland Plateau from east-Central Tennessee southward into Alabama to near the latitude of Birmingham. The anticline was breached by erosion during the late Tertiary, thereby producing Sequatchie Valley and revealing the details of its geologic structure—the anticline is thrust faulted on its northwest flank, and that thrust is now known to be part of a tectonic ramp that extends upward from the Lower Cambrian Rome Formation to flatten to the northwest into a higher detachment within the weak shale and coal beds in the Pennsylvanian deltaic sedimentary rocks. The same thrust emerges to the northwest as the Cumberland Plateau overthrust, and appears to be a mirror-image analog of the Pine Mountain fault located in the Plateau to the northeast. The purpose of this one-day field trip is to (1) provide an introduction to the Sequatchie Valley structure and the Mississippian-Pennsylvanian strata that form the crest and limbs of the anticline, and (2) gain some insight into the evolution of the topography in the southern Cumberland Plateau as the valley was exhumed during the late Tertiary. The first field trip stop is along Tennessee State Route (SR) 8 northwest of Dunlap to examine well-exposed rocks and structures along the upper detachment where it propagates along coal and shale beds in the Pennsylvanian section. The second field trip stop is up the southeast flank of the anticline along Tennessee SR-111 east of Dunlap to review the nearly continuous exposure of the Paleozoic section from the Devonian-Mississippian Chattanooga Shale to the top of the Mississippian.

Abstract The Pennsylvanian section on the southern Cumberland Plateau in the Sewanee and Tracy City area is composed of the Gizzard Group (Raccoon Mountain Formation, Warren Point Sandstone, and Signal Point Shale) and the lower portion of the Crab Orchard Mountains Group (Sewanee Conglomerate and Whitwell Shale). The hydrogeologic setting of the area controlled the founding and development of the town of Sewanee and University of the South. Water use initially relied upon a system of perennial springs, soil seeps, shallow wells, and a failed method of dam construction. Later, reservoirs with earthen dams across first-order drainages set the stage for growth of the community. Deformation associated with the Alleghanian Cumberland overthrust on the University Domain (more than 10,000 acres owned by the university) is subtle and confined to Bon Air coals in the Raccoon Mountain Formation, but a well-developed system of thrusts and folds in nearby Fiery Gizzard documents a consistent northwest tectonic transport direction. Deformation ranges from centimeter scale in Raccoon Mountain Formation mudstones to tens of meters of Warren Point Sandstone cut by northeast-striking thrusts. Deformation in Fiery Gizzard is locally related to two décollement surfaces above (intensely sheared Raccoon Mountain sandstone) and below (sheared Raccoon Mountain mudstones and coals) Sycamore Falls. Fourteen kilometers to the southeast, these overthrust structures are thought to connect to the Sequatchie thrust.

In the Appalachian orogen, the Neoproterozoic(?)–Lower Cambrian Chilhowee Group represents the initial drift-facies deposits along and across the eastern Laurentian continental margin following rifting. In the Southern Appalachians, this group forms thrust sheets along the west flank of the Talladega–Blue Ridge belt. Where the base is unfaulted, it lies depositionally above Ocoee Supergroup rift-facies rocks or Grenville basement. Regionally, the Chilhowee grades up into the Lower Cambrian Shady Dolomite, the initial deposits of the marginwide Cambrian–Ordovician carbonate bank. Sequences more interior to the orogen, including the Kahatchee Mountain Group (Talladega belt), the Nantahala and Brasstown Formations (western Blue Ridge), and the Hollis Quartzite (Pine Mountain belt), are considered to be correlative with the Chilhowee based upon similarities in lithostratigraphic sequence, sequence stratigraphy, sandstone provenance, and paleocurrent studies. Assuming an autochthonous Pine Mountain window, palinspastic restorations of foreland thrusts suggest that the Chilhowee Group restores essentially astride that window, and Chilhowee-equivalent units in the Talladega–Blue Ridge belts, in turn, restore farther southeast. This places the respective sequences southeastward in the order of increasing thickness and depth to basement from the base of the carbonate bank facies, with units restored farthest southeast having the most distal marine characteristics. Retro-deformation of thrust belt structures and the Pine Mountain cover sequence restores the Kahatchee Mountain Group at least to the subsurface position of the Wiggins-Suwannee suture, the southeastern limit of Laurentian continental crust, indicating that this group's basement was subducted beneath Gondwanan or peri-Gondwanan crust, and that the basement of even more outboard Laurentian sequences (e.g., eastern Blue Ridge) was overridden even farther.

Multiple levels of frontal ramps and detachment flats accommodate tectonic shortening in contrasting deformation styles at different levels in a mechanically hetero geneous stratigraphic succession in a foreland thrust belt. The late Paleozoic Appalachian thrust belt in Alabama exhibits a balance of shortening in contrasting deformation styles at different stratigraphic levels. The regional décollement is in a weak unit (Cambrian shale) near the base of the Paleozoic succession above Precambrian crystalline basement rocks. Basement faults, now beneath the décollement, controlled the sedimentary thickness of the Cambrian shale and the location of high-amplitude frontal ramps of the regional stiff layer (Cambrian-Ordovician massive carbonate); shortening in a mushwad (ductile duplex) from thick Cambrian shale is balanced by translation of the regional stiff layer at a high-amplitude frontal ramp above a basement fault. A trailing, high-amplitude, brittle duplex of the regional stiff layer has a floor on the regional décollement and a roof that is also the floor of an upper-level, lower-amplitude, brittle duplex. The roof of the upper-level brittle duplex is a diffuse ductile detachment below an upper-level mushwad, with which parts of the brittle duplex are imbricated. The basal detachment of the upper-level mushwad changes along strike into a frontal ramp at a location coincident with a sedimentary facies change in the weak shale unit that hosts the mushwad. The roof of the upper-level mushwad is a brittle massive sandstone. Shortening on the regional décollement is balanced successively upward through contrasting tectonic styles in successive mechanically contrasting stratigraphic units.