ABSTRACT This one-day trip highlights new findings on a preliminary bedrock geologic map that shows results from ongoing geologic mapping in the Falling Spring Valley of Alleghany County, Virginia, USA, which is the southern end of the larger Warm Springs Valley, an elongated anticlinal valley rimmed by Ordovician and Silurian siliciclastic rocks, and which is famous for its thermal springs. This mapping includes stratigraphic, structural, and karst field and lab research focused on the Ordovician strata exposed in the area, the oldest of which is the dolomitic upper part of the Beekmantown Formation (Lower Ordovician, Darriwilian), and the youngest of which is the Juniata Formation (Upper Ordovician, Katian), a sequence of siliciclastic redbeds. Warm Springs Valley is the location of the only known caves in the eastern United States—three at present—with thermal waters flowing in some of their passages. Stops on the trip will highlight key details from mapping efforts, primarily within the structurally deformed Ordovician carbonate sequence that is exposed in the core and limbs of the anticline, as well as the associated karst features that are developed in those carbonate rocks, including results of recent dye traces and water temperature monitoring that have improved our understanding of the karst hydrogeologic systems developed in these strata.

ABSTRACT A laterally discontinuous sandstone at the south end of the Tellico-Sevier syncline in Blount County, Tennessee, was mapped in 1955 by Robert Neuman and in 1965 by Neuman and Willis Nelson of the U.S. Geological Survey as a “quartzite” that they considered to be the uppermost bed of the Bays Formation (Ordovician). On the basis of new mapping and conodont biostratigraphy, lithostratigraphy, and regional K-bentonite correlations, this sandstone, a distinctive quartz arenite, is reassigned to and correlated with the Clinch Sandstone (Silurian). At the Harrison Branch section (HBRA) in Blount County, in an exposure near the confluence of Harrison Branch and the Little Tennessee River, this sandstone underlies the Devonian Chattanooga Shale, and it overlies ~43 m of gray limestones and shales that are themselves above the red clastic and minor carbonate rocks of the Bays Formation. The limestones and shales between the Bays Formation and this sandstone crop out on a wooded hillside and were apparently not observed by Neuman and Nelson during their mapping of the region. We measured the HBRA section, collected 20 samples from the limestone interval, and processed them for conodonts. These limestones contain a definitive Late Ordovician (Katian) conodont fauna that includes Drepanoistodus suberectus , Plectodina tenuis , Panderodus gracilis , and Phragmodus undatus . On the basis of this fauna, the 40+ m of limestone between the youngest red beds of unequivocal Bays Formation (below) and the quartz arenite (above) can be assigned to the Ordovician P. tenuis zone or younger, making them correlative regionally with limestones of the Trenton Group. Using these new biostratigraphic data combined with existing tephrostratigraphic relations of Ordovician K-bentonites, we identify the overlying sandstone at the HBRA section as an erosional outlier of the Silurian Clinch Sandstone, and we correlate the Ordovician-Silurian-Devonian unconformities at these two localities, which are now better constrained, with unconformities A through F in the Silurian and Devonian of this region, as identified and described in detail at several exposures north and northwest of the Tellico-Sevier syncline, most prominently at outcrops near Wytheville, Seven Mile Ford, and Max Meadows in southwest Virginia, where Devonian strata unconformably overlie Ordovician strata.

Abstract Burnsville Cove in Bath and Highland Counties (Virginia, USA) is a karst region in the Valley and Ridge Province of the Appalachian Mountains. The region contains many caves in Silurian to Devonian limestone, and is well suited for examining geologic controls on cave location and cave passage morphology. In Burnsville Cove, many caves are located preferentially near the axes of synclines and anticlines. For example, Butler Cave is an elongate cave where the trunk channel follows the axis of Sinking Creek syncline and most of the side passages follow joints at right angles to the syncline axis. In contrast, the Water Sinks Subway Cave, Owl Cave, and Helictite Cave have abundant maze patterns, and are located near the axis of Chestnut Ridge anticline. The maze patterns may be related to fact that the anticline axis is the site of the greatest amount of flexure, leading to more joints and (or) greater enlargement of joints. Many of the larger caves of Burnsville Cove (e.g., Breathing Cave, Butler Cave-Sinking Creek Cave System, lower parts of the Water Sinks Cave System) are developed in the Silurian Tonoloway Limestone, the stratigraphic unit with the greatest surface exposure in the area. Other caves are developed in the Silurian to Devonian Keyser Limestone of the Helderberg Group (e.g., Owl Cave, upper parts of the Water Sinks Cave System) and in the Devonian Shriver Chert and (or) Licking Creek Limestone of the Helderberg Group (e.g., Helictite Cave). Within the Tonoloway Limestone, the larger caves are developed in the lower member of the Tonoloway Limestone immediately below a bed of silica-cemented sandstone. In contrast, the larger caves in the Keyser Limestone are located preferentially in limestone beds containing stromatoporoid reefs, and some of the larger caves in the Licking Creek Limestone are located in beds of cherty limestone below the Devonian Oris-kany Sandstone. Geologic controls on cave passage morphology include joints, bedding planes, and folds. The influence of joints results in tall and narrow cave passages, whereas the influence of bedding planes results in cave passages with flat ceilings and (or) floors. The influence of folds is less common, but a few cave passages follow fold axes and have distinctive arched ceilings.

Abstract This two-day trip highlights new findings from structural, stratigraphic, and petrologic research in the Valley and Ridge province of Highland, Bath, and Augusta Counties, Virginia, and Pendleton County, West Virginia. The structural emphasis on Days 1 and 2 will be at several scales, from the regional scale of folds and faults across the Valley and Ridge, to outcrop-and hand sample-scale structures. Stops will highlight deformation associated with previously unmapped faults and a second-order anticline in Silurian and Lower Devonian carbonate and siliciclastic strata, specifically the Silurian Tonoloway Limestone, the Silurian–Devonian Helderberg Group, and the Devonian Needmore Shale. The stops on Day 1 will also focus on facies changes in Silurian sandstones, the stratigraphy of the Keyser–Tonoloway formational contact, and new discoveries relevant to the depositional setting and regional facies of the McKenzie Formation in southern Highland County. The focus of the stops on Day 2 will be on the petrology and geochemistry of several exposures of the youngest known volcanic rocks (Eocene) in the eastern United States. Discussions will include the possible structural controls on emplacement of these igneous rocks, how these magmas and their xenoliths constrain the depth and temperature of the lower crust and mantle, and the tectonic environment that facilitated their emplacement.

In the southeastern United States, identification of the Rocklandian Deicke and Millbrig K-bentonite Beds is based on differences in phenocryst mineralogy in the tuffaceous zones of each bed, and the two beds can be reliably and consistently distinguished on this basis. The common phenocrysts in the Deicke are labradorite and various Fe-Ti minerals, and in the Millbrig they are andesine, quartz, and biotite. Phenocrysts present in trace amounts are biotite and quartz in the Deicke, and apatite and zircon in both beds. The Deicke is altered dacitic or latitic ash, whereas the Millbrig is altered rhyodacitic ash. Both beds are interpreted as airfall deposits produced by huge volcanic eruptions, each of which was much larger and produced far more ash than the 1815 eruption of Tambora and even the great Toba eruption of 75 Ka. The principal authigenic minerals are feldspars (albite and K-feldspar), the clay minerals mixed-layer illite/smectite (I/S) and kaolinite, and ferroan and ferrotitanian minerals (pyrite, hematite, and the TiO 2 , polymorphs). The current lateral distribution of these authigenic minerals is the result of variations in regional geochemical conditions during burial diagenesis. The distribution of authigenic feldspars, together with regional changes in the percentage of illite in the I/S, indicates that maximum burial temperatures were higher in the Valley and Ridge province than along the Cincinnati Arch, and that the highest temperatures were in the Virginia Valley and Ridge. Regional variations in the distribution of the ferroan and ferrotitanian authigenic minerals in the K-bentonites and adjacent strata reflect variations in pore water redox conditions during diagenesis. Throughout the Cincinnati Arch and the westernmost Valley and Ridge, sediment pore waters were reducing. In the eastern Valley and Ridge of Alabama and Georgia the pore waters were oxidizing, and in the central and eastern Valley and Ridge from south of Roanoke to Knoxville the pore waters were initially reducing and then oxidizing. The stratigraphy of the Deicke and Millbrig is now very well known from their type area in the Upper Mississippi Valley to the easternmost exposures of Rocklandian strata in the southern Valley and Ridge from Alabama to Virginia. Many previous correlations are verified, and correlation of the two beds is extended along and across strike in the Valley and Ridge between Roanoke, Virginia, and Birmingham, Alabama. The Deicke and Millbrig are the thickest and most wide-spread of the several Rocklandian K-bentonites in this region. Of the two, the Deicke is more laterally persistent along the Cincinnati Arch, but in the southern Valley and Ridge the Millbrig is the more widespread and persistent of the two beds. The relationship of the K-bentonites to several regional and local unconformities is also now better understood. With this documentation of the great lateral extent of these two superb marker beds, it will be possible to link the vertical and lateral distribution of stratigraphically important faunal elements, especially conodonts and graptolites, with the stratigraphic position of the Deicke and Millbrig K-bentonite Beds.