Saltville Thrust Research Articles

Self‐similar cataclasis in the Saltville thrust zone, Knoxville, Tennessee

Fault rocks from the Saltville thrust zone, Knoxville, Tennessee, display a fractal geometry of clast size over 3 orders of magnitude. The cataclastic fractal geometry occurs at each magnification in different clast size classes and at combined magnifications. The mean of the fractal dimension (D) measured at each of the optical photomicrographs is generally smaller than that of the scanning electron microscopy images because of the smaller clast density in the optical sections. The fractal dimensions measured on randomly selected areas of the sections cut parallel to the thrust and normal to the thrust along the dip and strike, show a normal distribution with its mean, median, and mode that correlate closely with the dimension of ideal, fractal cataclasis (DI) based on the Sierpinski carpet model. The cataclasis was a statistical random, isotropic, and homogeneous fractal process that deformed the carbonates similarly parallel and normal to the thrust plane and in different parts of the thrust zone.

Displacement transfer at thrust terminations: the Saltville thrust and Sinking Creek anticline, Virginia, USA : Journal of Structural Geology, 16(6), 1994, pp 781–793

Displacement transfer at thrust terminations: the Saltville thrust and Sinking Creek anticline, Virginia, USA : Journal of Structural Geology, 16(6), 1994, pp 781–793

Displacement transfer at thrust terminations: the Saltville thrust and Sinking Creek anticline, Virginia, U.S.A.

The Saltville thrust terminates in the core of the Sinking Creek anticline. Changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination. Consequently, thrust displacement would be transferred into the fold. We combine newly published maps and new strain and mesostructural data from the Tuscarora Sandstone to argue that the Sinking Creek anticline did perform this kinematic role. We propose that the anticline developed as a fault-propagation fold that experienced both décollement and anticlinal breakthrough by the Saltville thrust. Thrust displacement was accommodated by the development of the modified fault-propagation fold and by transfer to a roof flat from the décollement breakthrough. New strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding. Consequently, layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough. Towards the plungeout of the Sinking Creek anticline, the displacement on the Saltville thrust is transferred to a floor thrust. We apply this interpretation to the termination of the St. Clair thrust, which has a similar surface geometry where the thrust terminates into an anticline. A testable implication of this proposed interpretation for the St. Clair thrust is that the Appalachian Plateau must absorb over 20 km of thrust displacement as horizontal shortening.

Interaction of cataclasis and pressure solution in a low-temperature carbonate shear zone

The mineralogical and elemental variations across the main shear zone of the Saltville thrust at Sharp Gap in Knoxville, Tennessee, U.S.A., were studied in a suite of deformed and undefromed carbonate rock samples using X-ray diffraction and electron microprobe methods. An examination of the samples for deformation effects at mesoscopic scale and under the optical microscope reveals familiar cataclastic deformation features including foliated cataclasites and microbreccias occurring in a well-defined, 1–2 m wide zone of intense deformation, plus evidence of hydrofracturing and extensive syndeformational pressure solution. There exists a clear correlation between the observed cataclastic deformation and mineral and elemental distribution which we interpret to result from a deformation-induced dolomite to calcite transformation in the shear zone. The transformation has resulted in removal of Mg from the shear zone, selective deposition of calcite as an intergranular cement in cataclasite/microbreccia units and a relative increase in the concentration of detrital quartz and feldspars. The compositional difference between the shear zone and wall rocks is explained in connection with cataclastic deformation features in terms of a model in which a dual pressure-solution/cataclastic flow mechanism leads to a gradual cementation-hardening of segments of the shear zone. Instabilities could occur via permeability reduction and increased pore pressure within these segments. Hydrofracturing of the hardened segments along with high strain rate reordering of the shear zone materials reset the ruptured zone back to the dual deformation mechanism regime. As a long-term effect, the compositional transformation of the shear zone is expected to prolong periods of creep and cause smaller coseismic stress drops since under the imposed conditions calcite is more ductile and soluble than dolomite.

Implications of Thermal Events on Thrust Emplacement Sequence in the Appalachian Fold and Thrust Belt: Some New Vitrinite Reflectance Data

Interpretation of existing geothermometry data combined with new vitrinite reflectance data, within the framework of a detailed composite tectonic setting, elucidates the evolution of structural sequencing of thrust sheets during the Alleghanian event in the Valley and Ridge Province in Virginia. That the Pulaski thrust sheet preceded the Saltville thrust sheet in the emplacement sequence, and that both reached thermal maxima prior to, or during, respective emplacement may be inferred from vitrinite and other geothermometry data. In contrast, the Narrows and St. Clair thrust sheets probably each attained their thermal maximum after emplacement. New vitrinite reflectance data are consistent with CAI and other temperature-sensitive information heretofore ascertained in the Valley and Ridge Province and support previously established maximum temperatures of ca. 200°C for strata of the Saltville thrust sheet as young as Mississippian. $$R_{max}$$ values from Mississippian coals in the Price Formation of the Saltville sheet, beneath but near the Pulaski thrust, range from 1.61% to 2.60%. At the structural front of the fold and thrust belt, a single Mississippian coal sample from the Bluefield Formation yields an $$R_{max}$$ value of 1.35%. Those coals showing highest $$R_{max}$$ values are more intensely fractured with secondary minerals filling the fractures. Warm fluids introduced during tectonic events may have played at least as important a role as that of combined stratigraphic and tectonic burial.

Relationships between early Paleozoic facies patterns and structural trends in the Saltville thrust family, Tennessee Valley and Ridge, southern Appalachians

Structural style variations across the Tennessee segment of the Valley and Ridge thrust belt are correlated with two facies changes in important structural/stratigraphic units. The Middle and Upper Cambrian Conasauga Group and the Middle Ordovician Chickamauga Group change their internal stratigraphy regionally at oblique angles to the trend of this segment of the thrust belt. These stratigraphic variations correlate geographically with structural style changes within individual thrust sheets, whereas other variables, such as temperature, pressure, and magnitude of tectonic transport, do not. In the Conasauga, the east to west, limestone to shale facies transition coincides with areas where structural styles change along thrusts at the Conasauga level. The shale-dominated and carbonate-dominated facies show simple frontal imbricate thrusts, whereas in the shale/carbonate zone of interlayering, duplexes occur. In the Chickamauga, an east-west change from basinal shale to shelfal limestone controlled the regional presence of a middle-level glide zone in the paths of eastern thrusts and its absence to the west. This stratigraphic inhomogeneity also controlled a change in the Knoxville area from surficial folding in the northeast to surficial thrusting in the southwest. The terminology of structural lithic units and their subsidiary predominant and conforming members is applied in dividing the stratigraphic section into structurally significant packages.

Alternative Stratigraphic Interpretations for Thrust Sheets Beneath Southern Appalachian Crystalline Overthrust: ABSTRACT

In eastern Tennessee, strata as young as Mississippian lie directly beneath the Great Smoky thrust. There, a stack of three sheets (Pulaski, Saltville, and Copper Creek) contains an estimated thickness of 19,000 ft of sedimentary rocks above Precambrian basement. Seismic profiles obtained as part of the site study for the proposed Appalachian Ultra-deep Core Hole (ADCOH), 85 mi southeast of the Great Smoky fault, have been interpreted to reflect subhorizontal Paleozoic strate about 5,000 ft thick beneath overthrust crystalline rocks and above autochthonous crystalline basement. The most remarkable relationship to be explained is not that subhorizontal Paleozoic strate extend southeastward to the ADCOH site east of the Brevard zone, but rather by what mechanism such a great thickness of Paleozoic strata in several thrust sheets is lost southeastward. Six alternative scenarios of a structural cross section from eastern Tennessee to the ADCOH site show the proposed core piercing a single subhorizontal stratigraphic succession formed by (1) attached platform strata, (2) the Copper Creek thrust sheet, (3) the Saltville thrust sheet, (4) the Pulaski thrust sheet, (5) a previously unknown thrust sheet that came from the eastern platform margin slope of North America, and (6) a thrust sheet of terrane accretedmore » from another continent, probably Africa. The subhorizontal strata at the ADCOH site also may represent a stacking of thrust sheets, each containing only part of the stratigraphic thickness preserved farther northwest. Stratigraphic criteria will permit identification of a specific thrust sheet or of stacked thrust sheets in the core hole. The indicated southeastward thinning of strata in thrust sheets beneath the crystalline overthrust raises questions about foreland thrusting mechanisms.« less

Structural evolution of the Pulaski thrust system, southwestern Virginia

The Pulaski fault system is a complex series of Alleghanian thrusts which has juxtaposed rocks of the Pulaski thrust sheet over rocks as young as Early to middle Mississippian (Maccrady Formation) of the Saltville thrust sheet. The Salem branch, a later major branch of the Pulaski fault system within the Pulaski thrust sheet, displaced the complexly deformed plate containing a broken formation (a lithotectonic assemblage of complexly folded and faulted Elbrook and Rome carbonates and shales with associated breccias) over rocks as young as Early Mississippian (lower Price Formation) of the Salem synclinorium. The classic, ubiquitous Max Meadows breccias generally are confined to the broken formation, which forms the basal part of the complexly deformed plate and which is interpreted as an exhumed lower level decollement zone formed during an earlier Alleghanian stage and transported during a later Alleghanian stage of deformation to a much higher structural level. Minimum displacement of the complexly deformed plate is on the order of 100–110 km, on the basis of a new palinspastic reconstruction of the Pulaski thrust sheet. On the basis of this reconstruction and of two balanced and restored cross sections for the western portion of the Valley and Ridge, minimum shortening for the Pulaski thrust sheet is ∼80%, whereas that for the western part of the Valley and Ridge province is only ∼10%–20%. The Pulaski fault system is interpreted to have originated below the Appalachian-wide basal decollement zone near the contact between the Cambrian Rome and Elbrook Formations.

Structural Complexity Associated with Transfer Zone: An Example from Southern Appalachians: ABSTRACT

Transfer zones provide a mechanism by which displacement is maintained across a fold and thrust belt where a single thrust terminates along strike. Commonly, the transfer is not simply a lap joint wherein en echelon thrusts, tied to a common sole fault, shift displacement; rather, these zones are structurally complex with intensified folding, fracturing, and, in some instances, cleavage. An example occurs in the Valley and Ridge of eastern Tennessee, northeast of Knoxville. There, the Beaver Valley thrust terminates into folded Middle Ordovician carbonates. To the southeast, the adjacent Saltville thrust increases in stratigraphic separation, coinciding with the Beaver Valley termination. The Saltville places Lower Cambrian strata on Mississippian units northeast of the fault termination, whereas the Lower Cambrian rests on Cambrian-Ordovician rocks only 20 km to the southwest. Near its tip, the Beaver Valley thrust shows little displacement, but the loss of slip is accompanied by intensified folding. The folding traces an anticlinorium involving Middle and Upper Ordovician carbonates and shales. These folded rocks are broken by fractures and extensional veins, commonly filled with sparry twinned calcite, and ranging from 0.2 to 2.0 mm wide. One set of veins is generally normal to bedding with a second set oblique; in some cases, three sets cut the rock. Also, Middle Ordovician carbonates carry an axial planar solution cleavage, and catacalcites are locally developed, particularly in dolostones of the Cambrian-Ordovician Knox Group. A set of folds, the axes of which are oblique to transport direction, occurs across the transfer zone; they are often found in he footwall of a thrust. The complex structural geometries in these thrust sheets suggest contradictory timing relationships. The contradiction is explained if the two faults are envisioned as propagating from initial breaks, then growing toward one another contemporaneously. This example demonstrates the potential complexity of a transfer zone, as well as the possibility of apparent local variation in fault sequence in a generally hinterland to foreland progression of emplacement. End_of_Article - Last_Page 1440------------

Schurflingsfensters in Pulaski Thrust Sheet and Their Implications for Hydrocarbon Potential: ABSTRACT

Highly deformed Cambrian through Devonian rocks are exposed in fensters in the Pulaski thrust sheet of the Virginia Valley and Ridge province. Detailed mapping of these exposures shows a consistency of structural style--namely, faulted, stacked antiforms with duplex geometry and folded roof thrusts. Strain intensity and the style of regional folds and faults suggest that the fensters are schurflingsfensters that expose rootless tectonic slices, or horses, possibly derived from a thrust ramp in the trailing part of the subjacent Saltville thrust sheet. Recent interpretations of the U.S. Geological Survey's central Virginia seismic line place this ramp east of and below the crystalline rocks of the Blue Ridge structural front. Geometric modeling of rocks in the schurflingsf nsters suggest the existence of possible Cambrian through Mississippian hydrocarbon-bearing rocks below the Pulaski, Max Meadows, and Blue Ridge thrust sheets. Rock samples from horses are presently being collected to determine thermal maturity and source rock potential. If these rocks were derived from the Saltville thrust sheet, sampling should prove important in evaluating hydrocarbon potential below eastern thrust sheets of the Appalachian Valley and Ridge, and Blue Ridge provinces. End_of_Article - Last_Page 1447------------

Displacement Transfer at Thrust Terminations in Southern Appalachians--Saltville Thrust as Example

Transition from faulting to noncylindrical folding, involving rapid plunge change at the fold closure, is the primary displacement transfer mechanism at the northern end of the South Appalachian foreland fold and thrust belt. Regional thrust faults, including the Saltville, Narrows, and St. Clair, terminate in regional, overturned asymmetric anticlines. This mechanism of displacement transfer is distinct from thrust terminations where fold complexes of smaller, noncylindrical folds converge toward the end of the fault trace. The Saltville thrust transition to the Sinking Creek anticline is representative of the southern Appalachian structures. Deformation intensity patterns, reflected by cleavage development, mesoscopic folding, and faulting, suggest that the Sinking Cree anticline formed due to upwarping from shear thrusting at depth. Laboratory deformation analogs of folds formed above ramps support this contention. Experimentally produced folds are asymmetric overturned structures with high strains on overturned limbs and very low strains on upright limbs. A deformation sequence involving shear thrusting with subsequent break thrusting may characterize fault propagation at thrust termini. This will be important for layered sedimentary sequences where thick, rigid members low in the sedimentary pile are overlain by thinner, interbedded, mechanically anisotropic strata.

Cataclasites along the Saltville thrust, U.S.A. and their implications for thrust-sheet emplacement

Cataclasis and frictional wear are the primary bulk deformation mechanisms along steeply dipping portions of the Saltville thrust in the southern Appalachian foreland zone, U.S.A. Fault character ranges from a single discrete sliding surface with negligible gouge, to a zone of several discrete sliding surfaces or a zone (up to 0.3 m thick) of pervasive cataclasite. Marked fracturing occurs up to 20 m above the fault, whereas minimal deformation is found in the footwall rocks. Hanging wall dolomites range from crush breccias (less than 5% matrix) to ultracataclasites (with 90% matrix), although cataclasites (50–70% matrix) are predominant. Foliated cataclasites occur where dolomite is thrust over shale. Progressive development of cataclastic fabrics is due to comminution by fracturing and grinding along intersecting fractures. Continued frictional grinding results in complete disruption of the original fabric to produce cataclasite and minor ultracataclasite. Grain alignment occurs by rigid body rotation with subsequent local enhancement by pressure-solution. Microstructural relations of the fault gouge suggest periodic fluctuations in fluid pressure, where λ v (ratio of fluid to overburden pressure) probably ranged between 0.45 and 1. The Saltville thrust-sheet emplacement must have occurred in a caterpillar-like fashion involving aseismic and seismic shear. Shear stresses accompanying fault motion as determined from dolomite twin lamellae are in the order of 65 mPa.

Devonian Shale Exploration Rationale Tested in Northeast Tennessee: ABSTRACT

Devonian shale exploration rationales are characterized by some geologic fracture-creating mechanism, for natural fracture systems are essential to natural gas production, even with advanced stimulation technology. One rationale predicts intense fracturing in the shale wherever proximally associated with the major thrust faults of the Appalachian Valley and Ridge province. Gruy Federal No. 1 Grainger County, TN (DOE EGSP-TN9), tested this rationale. The well penetrated the Saltville thrust fault (stratigraphic throw over 10,000 ft or 3,048 m) and encountered 720 ft (220 m) of Devonian-Mississippian Chattanooga Shale in the lower plate. A total of 220 ft (67 m) of core was extracted from the most highly organic intervals of the shale, and a full suite of wire-line logs was run. Widespread and locally intense fracturing observed in the core and evidenced by the logs vindicates the exploration rationale. By the time this paper is presented the well will have been stimulated and the well test results will be available. End_of_Article - Last_Page 1283------------

Cambrian Facies Trends--Tool for Estimating Shortening in Southern Valley and Ridge Province: ABSTRACT

Regional stratigraphic study of the Nolichucky Shale (Upper Cambrian) northwest of the Saltville thrust fault in the Oak Ridge-Knoxville area, Tennessee, delineated the areal extent of a large lobate algal stromatolite bank. Because the bank has limited geographic distribution, it was possible to identify its edge from northwest to southeast, in the Pine Mountain, Wallen Valley, Clinchport, and Copper Creek fault belts. These thrust faults strike at an oblique angle to the original trend of the algal bank, so that from northwest to southeast different parts of the bank are juxtaposed. Facies changes within the bank sequence permit palinspastic restoration of the original bank that indicates the total movement of the Pine Mountain, Wallen Valley, Clinchport, and Copper Cre k thrust faults is about 40 mi (64 km). Although these data are limited to the west half of the Valley and Ridge, continuing study toward the south and east may lead to an estimation of total shortening across the entire Valley and Ridge province. End_of_Article - Last_Page 1892------------

Relations of Bouguer Gravity Anomalies to Geological Structure in the New River District of Virginia

Over 500 gravity observations were made at 2- to 3-km intervals along accessible roads in the New River District of Virginia, within an area defined by lat 37°009N., and 37°309N., and long 80°159W. and 81° 009W. The Bouguer anomalies of the data can be related to variation in crustal thickness, and folding and faulting in the Appalachian Valley. A quadratic polynomial surface fitted to Bouguer anomaly data by a least squares process reveals a broad anomaly trending north-northeasterly across the area. This anomaly correlates well with the gravity field associated with variation in crustal thickness determined from a seismic survey of the Middle Atlantic states. Residual gravity anomalies obtained from differences between the Bouguer anomalies and the quadratic polynomial surface indicate an east-northeasterly trending feature which parallels the regional strike of the Appalachian geological structure. This residual gravity anomaly of approximately 8 mgal can be explained by a structural model based upon attitudes of sedimentary units measured at the surface and density values measured from outcrop specimens. This interpretation suggests that the Blacksburg syncline consists of approximately 7 km of Paleozoic sedimentary rocks. There is no indication in the gravity data of any major decollement. Numerous local residual anomalies 2 to 3 mgal in amplitude are observed over the Pulaski and Saltville thrust faults. These anomalies may be associated with the extensive breccia zones exposed in the near surface material and with the variation in the thick-nesses of thrust plates.

Trenton and Sub-Trenton Stratigraphy of Northwest Belts of Virginia and Tennessee

The Lower Cambrian Rome is the oldest formation exposed in the northwest belts of Virginia and Tennessee. The formation consists of thick clastics, the shales apparently serving as the loci of thrusting along several of the northwest thrust blocks of Tennessee. The overlying Conasauga group, largely shale northwest in Tennessee, grades through shales and limestones into dolomitic limestones and dolomite southeast and east, reflecting a general northwestward to westward source. Analyses of the more persistent sandstone units at the top of the overlying Copper Ridge dolomite suggest a similar source direction. The Copper Ridge (Upper Cambrian) and Beekmantown (Lower Ordovician) dolomites grade southeastward into limestones, the gradation isoliths closely coinciding with a s ructural barrier of some nature. This barrier is presumably an arch (Tazewell arch) quite similar to, and probably an extension of, the Adirondack arch on the northeast, and possibly is in part coincident with the Rome barrier of Ulrich. The trend of the Tazewell arch coincides closely with the present position of Clinch Mountain in Virginia and Tennessee. The Saltville thrust closely outlines the trend of the arch along the southeast flank. Middle Ordovician rocks southeast of the Tazewell arch are thick and highly clastic, indicating a rejuvenation of the landmass source on the southeast and an accompanying shift in the source direction to the southeast. The Tazewell arch was particularly effective in separating typically geosynclinal rocks from the foreland rocks on the northwest, being more effective in Tennessee than in Virginia. Pre-Trenton, post-Beekmantown units thin by convergence and overlap from approximately 4,600 feet southeast of the arch (southeast of Knoxville, Tennessee) to approximately 1,000 feet northwest of the arch near the Kentucky-Tennessee line. The same interval thins along the strike of the foreland rocks from 1,400 feet in Lee County, Virginia, to approximately 500 feet in Pendleton County, Wes Virginia. Isopachs of this interval are fairly closely parallel with the Tazewell-Adirondack axis trend. Recent oil developments in the area of the Cumberland thrust block in Lee County, Virginia, have created additional interest in the northwest outcrop belts. Oil has been produced from the Trenton, Eggleston, and Lowville limestones, with a showing from the Beekmantown dolomite. The rock porosity is not well understood. Field indications suggest fracture porosity.

Lower Middle Ordovician of Southwest Virginia and Northeast Tennessee

The lower middle Ordovician of southwest Virginia and northeast Tennessee may be divided into 29 lithologic and faunal units, many of which are remarkably persistent throughout the area. Important lithologic changes were largely attributed to the presence or absence of individual units in the section, while changes by lateral gradation were considered of importance only in restricted parts of the section and in somewhat localized areas. Barrier control of facies is well illustrated by the comparison of the limestones directly northwest and southeast of Clinch Mountain in Virginia. The two median belts directly autochthonous to the Saltville thrust show the most complete sections, containing in some areas all of the lithologic and faunal units of the standard section of Tazewell County, Virginia. Evidence of a large hiatus was observed in the northwest belts of the Saltville autochthone, indicating northwestward convergence of some of the units. The sections southeast of Clinch Mountain (Saltville allochthone) are considerably thicker and more clastic than those northwest of Clinch Mountain. Limestones of the latter area thicken and become more clastic along the strike of the median belts from Virginia into Tennessee. Detailed sections measured along seven belts were compared with the revised classification of Tazewell County, Virginia. The Blackford, Five Oaks, Lincolnshire, Thompson Valley (new), upper Peery, Benbolt, Wardell, Bowen, Witten, and Moccasin formations extend into northeast Tennessee. The Ward Cove (restricted), lower Peery, and Gratton formations largely disappear in southwest Virginia. The Mosheim, Holston, Ottosee, and Bays should be discontinued as definite formational names. The further use in this area of such terms as Stones River group, Blount group, Murfreesboro limestone, and Lowville limestone is not recommended. The Lenoir limestone and Sevier shale were redefined to preserve their validity. The Holston marble of the Knoxville, Tennessee, area was assigned a new name. The current classification of major boundaries in Virginia and Tennessee needs revision but should await further detailed comparisons with the standard sections.