ABSTRACT This field guide highlights the Paleozoic geology of the Knoxville, Tennessee, area, framed in the context of the historic, halcyon days of Knox County’s marble industry and the railroads built to serve the area’s many limestone quarries and mills. The Three Rivers Rambler excursion train (the “Rambler”) is pulled by an 1890 “Consolidation” steam locomotive, which has been restored and is now operated by the Knoxville & Holston River Railroad Co., Inc. The Rambler route follows the north bank of the Tennessee River; passes through a sequence of Lower and Middle Ordovician carbonates, shales, and sandstones of the Knox and Chickamauga Groups; crosses the High Bridge at the confluence of the Holston and French Broad Rivers; and ends near Marbledale Quarry before returning to Knoxville. The two geologic groups are dominated by carbonates and lie in the syncline that contained most of the commercial marble that was quarried in the Knoxville area for the past 150 years. Exposures of the Holston Formation, a limestone commercially referred to as Holston [M]arble, were excavated to build the railroad ~125 years ago. It is possible to observe four of the seven formations making up the Knox and Chickamauga Groups along the route, but the outcrops are not accessible during typical railroad operations or by automobile. Arrangements were made for a field trip during the 2018 Geological Society of America Southeastern Section meeting, and this guide provides details for four selected exposures between Knoxville and the Forks of the River Marble District, with three optional stops. Only during the field trip, passengers will be able to disembark the train to examine carbonate and shale outcrops, structures, and discuss facies relationships of the foreland basin bryozoan reef deposits along the western flank of the Taconic (Sevier) foredeep. In addition to the local geology, this field guide describes the key role of railroads in the development of the Knox County marble industry, the history of what is today the Knoxville & Holston River Railroad, a corporate descendent of the 1887 Knoxville Belt Railroad Company, and the Tennessee Marble industry.

ABSTRACT The geology of Great Smoky Mountains National Park (GRSM) in Tennessee and North Carolina is dominated by siliciclastics and metamorphic strata. However, in the western portion of GRSM, a series of carbonate fensters (windows) expose the Lower Ordovician–age section of the Knox Group, a series of dolomite and limestone units that are partially marbleized as a result of contact metamorphism from the Great Smoky fault. The fensters create opportunities for allogenic recharge to occur at points along the contact of the surrounding insoluble strata with the underlying soluble carbonates. The combination of chemically aggressive surface recharge and vertical relief has resulted in the formation of deep caves, many of which have active streams and water resources. Though the karst is limited in extent and the number of caves is fairly small, the significance of the resources is substantial, with several of the caves in the area over 150 m in depth and at least two being major bat hibernacula. In 2017, the U.S. Geological Survey (USGS) began a study to better understand the hydrologic behavior of these karst systems through hydrologic and geochemical monitoring, groundwater tracing using fluorescent dyes, and seepage runs. Stage and water-quality instrumentation was installed in two caves in GRSM, the main stream of Bull Cave, and in a sump pool in Whiteoak Blowhole, at 173 m and 70 m below land surface, respectively. Following setup of the cave sites, dye injections were conducted to determine discharge points for four of the deep cave systems on Rich Mountain and Turkeypen ridge. Results show water in these systems has an extremely rapid travel time, with tracers detected from caves to springs in less than 24 h for each of the systems. This field guide describes the complex geology, regional hydrogeology, and unique landscape characterized by high-gradient subterranean streams, carbonate fensters, and deep caves of the GRSM karst.

Abstract In response to rising concerns about atmospheric carbon dioxide (CO 2 ) levels and likely regulations on emissions, investigations into geologic carbon storage options across the United States are underway. In the Midwest, Cambrian sandstones are major targets for potential geologic carbon storage. In some localities, the overlying Cambrian–Ordovician Knox Group is also being investigated as a possible target for primary and secondary storage of CO 2 . The thick dolomitic succession contains intervals that may function as both reservoirs and seals. Gas storage fields in Knox carbonates in Kentucky and Indiana demonstrate that methane can be safely stored in paleotopographic highs along the Knox unconformity surface. Numerous injection wells have also been completed in the Knox Group for brine disposal. More significantly, at least seven class 1 injection wells have used the Knox as all or part of a storage reservoir for industrial wastes. Many of these wells have injected millions of gallons of liquid waste annually into Knox reservoirs. The relative scale of these injection operations can be used to estimate the types and sizes of potential reservoirs within the Knox succession in the Midwest. Specific data on the Knox interval relative to its carbon storage and confining potential are currently being collected from wells drilled as part of U.S. Department of Energy administered carbon storage projects, as well as state-administered carbon storage programs. In this chapter, initial results of carbon storage tests are summarized from the Battelle 1 Duke Energy well, Kentucky Geological Survey 1 Blan well, Battelle-American Electric Power (AEP) 1 Mountaineer well, and Battelle-Ohio Geological Survey 1 CO 2 well. The AEP Mountaineer Power Plant will host the nation’s first commercially integrated carbon capture and geologic storage project, and the storage reservoirs will be in the Knox Group. Because the Knox Group is widespread at depth across much of the Midwest, it will be an important part of sequestration programs as confining interval and reservoir.

Data from thousands of coalbed methane wells, conventional oil and gas wells, and five regional seismic-reflection profiles show evidence of relationships among multiple extensional events and Appalachian thrusting in the area of the Alabama Promontory and Black Warrior Basin. The oldest extensional event is of late Precambrian to early Middle Cambrian age, associated with Iapetan rifting. Along the southeastern margin of the promontory, in the northeastern part of the Birmingham graben system, a fill sequence older than the Rome Formation (Early Cambrian) is inferred. Normal faults along both sides of the promontory were active from Early Cambrian to early Middle Cambrian, as indicated by expanded hangingwall sections of the Rome and Conasauga Formations. In the Black Warrior Basin, some basement-involved normal faults were active during deposition of the Ketona and Knox carbonates (Late Cambrian–Early Ordovician). Middle Cambrian to Early Ordovician extension coincided with the inception and opening of the Rheic Ocean. Small amounts of growth occurred on some normal faults and on folds at the leading edge of the Appalachians during deposition of the Pottsville Formation (early Pennsylvanian, Morrowan). Major thin-skinned and basement-involved normal faulting occurred in the Black Warrior Basin after deposition of the preserved Pottsville section, probably during Atokan time. The extensional thin-skinned detachments are in or at the base of the Pottsville Formation and the top of the Conasauga Formation. Major Appalachian thrusting occurred after the main episode of normal faulting, perhaps during the late Pennsylvanian.

Abstract In the eastern mid-continent United States, the Cambrian Mt. Simon Sandstone is a likely deep-saline reservoir target for CO 2 sequestration. The overlying Cambrian–Ordovician Knox carbonate section will be an important part of the confining interval for the Mt. Simon, as much of the Knox is dominated by dense (<0.01 md), well-cemented dolomites with little or no permeability. The Knox, however, does contain discrete zones of porosity and permeability and is locally an important oil and gas producer, as well as gas storage unit. The Knox needs to be considered in any sequestration project in the region because in some localities carbonate and sandstone zones within the unit have better reservoir characteristics than the underlying Mt. Simon or overlying St. Peter Sandstone. An example of such a locality is the DuPont waste-injection site at Louisville, Kentucky, where a thick Mt. Simon section was tested and then abandoned in favor of a fractured, vuggy dolomite facies in the overlying lower Knox with an injectivity rate as high as 568 liters per minute (150 gallons per minute). Thick, dense carbonates of the Knox enveloped the reservoir effectively sealing the porous and permeable zones within the same stratigraphic unit. This is not an exceptional circumstance because several deep tests of Cambrian–Ordovician clastics in the region have encountered tight sandstone in the target horizon but vuggy and fracture porosity in overlying Knox carbonates. Analyses of known Knox enhanced oil recovery operations, waste-injection wells, and gas storage fields illustrate that liquids and gases can be effectively and safely retained within Knox reservoirs. However, porous and permeable zones within the units that constitute the local reservoirs are discontinuous and heterogeneous, and data describing the detailed characteristics of these reservoirs are sparse. More deep subsurface data are needed to better characterize the Knox and similar carbonates in other regions for their use as potential carbon sequestration reservoirs. Some of these data are currently being collected through the U.S. Department of Energy’s Carbon Sequestration Regional Partnership programs.

Abstract Deeply buried reservoir strata in the Illinois Basin may be targeted for carbon sequestration, but only if discontinuities that may affect the reservoir and its overlying sealing strata can reliably be detected and mapped in three dimensions. Detection and mapping of subtle discontinuities (e.g., faults) are critical factors in assessing a potential carbon sequestration reservoir because such structures may affect the integrity of the reservoir seal or affect the connectivity within the reservoir itself. In this study, we apply and assess various techniques to enhance the interpretation of the deep structure of a small oil field in the Illinois Basin called the Tonti field. Techniques used include three-dimensional (3-D) spectral decomposition and semblance, combined with other seismic attributes, to demonstrate the crucial need for broad bandwidth data and continuity-based seismic attributes when dealing with the very subtle structural discontinuities that characterize the Illinois Basin. The coincident application of enhancement techniques to both two-dimensional (2-D) and 3-D seismic data from the same geological feature emphasizes the value of tracing discontinuities within 3-D seismic attribute volumes as opposed to using single profiles or even a network of profiles. The results show that 3-D seismic analysis can identify discontinuities at or near the sealing horizon (base of the Cambrian–Ordovician Knox Group at or near the top of the Cambrian Mt. Simon Sandstone), whereas on conventional 2-D seismic profiles, these discontinuities are at best subtle and difficult or impossible to interpret. From the 3-D seismic data for the Tonti field, these discontinuities appear to be associated with the folding of overlying strata, although a nontectonic origin cannot be ruled out. In general, this type of analysis can focus the attention on potential problem areas for sequestration; however, the seismic data analysis alone cannot determine if reflector discontinuities necessarily imply potential leakage but can decrease the uncertainty in evaluation.

The deformed wedge of Paleozoic sedimentary rocks in the southern Appalachian foreland fold-thrust belt is defined by the configurations of the undeformed basement surface below and the base of the Blue Ridge–Piedmont megathrust sheet above, together with the topographic free surface above the thrust belt. The base of the Blue Ridge–Piedmont sheet and undeformed basement surface have been contoured using industry, academic, and U.S. and state geological survey seismic-reflection and surface geologic data. These data reveal that the basement surface dips gently SE in the Tennessee embayment from Virginia to Georgia, and it contains several previously unrecognized normal faults and an increase in dip on the basement surface, which produces a topographic gradient. The basement surface is broken by many normal faults beneath the exposed southern Appalachian foreland fold-thrust belt in western Georgia and Alabama closer to the margin and beneath the Blue Ridge–Piedmont sheet in Georgia and the Carolinas. Our reconstructions indicate that small-displacement normal faults form beheaded basins over which thrust sheets were not deflected, whereas large-displacement normal faults (e.g., Tusquittee fault) localized regional facies changes in the early Paleozoic section and major Alleghanian (Permian) structures. These basement structures correlate with major changes in southern Appalachian foreland fold-thrust belt structural style from Virginia to Alabama. Several previously unrecognized structures along the base of the Blue Ridge–Piedmont sheet have been interpreted from our reconstructions. Large frontal duplexes composed of rifted-margin clastic and platform rocks obliquely overridden along the leading edge of the Blue Ridge–Piedmont sheet are traceable for many kilometers beneath the sheet. Several domes within the Blue Ridge–Piedmont sheet also likely formed by footwall duplexing of platform sedimentary rocks beneath, which then arched the overlying thrust sheet. The thickness and westward limit of the Blue Ridge–Piedmont sheet were estimated from the distribution of low-grade foot-wall metamorphic rocks, which were observed in reentrants in Georgia and southwestern Virginia, but are not present in simple windows in Tennessee. These indicate that the original extent of the sheet is near its present-day trace, whereas in Georgia, it may have extended some 30 km farther west. The southern Appalachian foreland fold-thrust belt consists mostly of a stack of westward-vergent, mostly thin-skinned thrusts that propagated westward into progressively younger units as the Blue Ridge–Piedmont sheet advanced westward as a rigid indenter, while a few in northeastern Tennessee and southwestern Virginia involved basement. Additional boundary conditions include temperatures <300 °C and pressures <300 MPa over most of the belt. The southern Appalachian foreland fold-thrust belt thrusts, including the Blue Ridge–Piedmont megathrust sheet, reach >350 km displacement in Tennessee and decrease both in displacement and numbers to the SW and NE. Much of the Neoproterozoic to Early Cambrian rifted-margin succession was deformed and metamorphosed during the Taconic orogeny, and it is considered part of the rigid indenter. Only the westernmost rocks of the rifted-margin succession exhibit ideal thin-skinned behavior and thus are part of the southern Appa-lachian foreland fold-thrust belt. Palinspastic reconstructions, unequal thrust displacements, and curved particle trajectories suggest that deformation of the belt did not occur by plane strain in an orogen that curves through a 30° arc from northern Georgia to SW Virginia. Despite the balance of many two-dimensional cross sections, the absence of plane strain diminishes their usefulness in quantifying particle trajectories. Coulomb behavior characterizes most individual faults, but Chapple's perfectly plastic rheology for the entire thrust belt better addresses the particle trajectory problem. Neither, however, addresses problems such as the mechanics of fault localization, out-of-sequence thrusts, duplex formation, three-dimensional transport, and other southern Appalachian foreland fold-thrust belt attributes.