Characteristics of Thrust Fault Imbrication Along the Western Margin of the Blue Ridge Structural Province Buffalo Mountain, Tennessee

The Buffalo Mountain thrust sheet, located along the western margin of the Blue Ridge structural province in northeastern Tennessee, provides an excellent opportunity to examine transitional structural styles and deformational mechanisms between the Valley and Ridge and Blue Ridge. The Buffalo Mountain sheet is composed of a sequence of Lower Cambrian Chilhowee Group elastics that have been thrust over Upper Cambrian Conasauga Group shales and Cambre- Ordovician Knox Group carbonates. The entire stack has been imbricated into four interleaved thrust slices and is folded into a northeast trending doubly plunging syncline. Field mapping and indirect examination of thrust plane orientations reveal that all thrust faults in the area place older rocks over younger rocks, cut up stratigraphic section through both foot wall and hanging wall strata, and do not cross-cut or displace each other. These data suggest that the Buffalo Mountain area has experienced only one episode of contractional thrust faulting. The structural relationships at Canah Hollow, along the southwestern corner of the Buffalo Mountain sheet, are interpreted as a foreland-dipping duplex. The duplex is composed of horses torn away from both the foot wall Holston Mountain sheet and the hanging wall Buffalo Mountain sheet. The structural history of Canah Hollow provides an example of progressive deformation during a single episode of in-sequence thrusting. The small klippe of Unicoi within Canah Hollow was originally part of the Pinnacle sheet, and has been repositioned by either minor faulting, erosional collapse, or mass wasting. Small scale structures within the hanging wall rocks of the Buffalo Mountain thrust sheet include quartz-filled fractures, fractured grains, pressure solution traces, undulatory extinction, and just above the Buffalo Mountain thrust surface, ribboned quartz grains, and crenulation cleavage. The small scale structures associated with the foot wall rocks of the Buffalo Mountain sheet are characterized by a cataclastic fabric (crushed, cracked, and fractured grains) that lacks an internal foliation, styolitic pressure solution traces, and mineral-filled conjugate en echelon fractures. The large scale geometric relationships between major thrust sheets combined with the orientation of minor structures suggests that thrust sheet emplacement in the northeast Tennessee Blue Ridge has occurred in a hinterland to foreland fashion. Specifically, the folding of the Buffalo Mountain thrust sheet is probably due to the vise effect caused by the emplacement of the structurally lower, more foreland Limestone Cove duplex and Pulaski sheet. The absence of a strain contrast across the Buffalo Mountain sheet combined with the laterally overlapping geometry of the imbricate sheets suggest that the imbricate sheets formed simultaneously during folding. Thus, the Buffalo Mountain area provides a group of structurally complex features that have formed during a single progressive episode of hinterland to foreland thrusting

Stratigraphy, Sedimentary Petrology, and Depositional Environments of Tillite in the Upper Precambrian Mount Rogers Formation, Virginia

The upper member of the upper Precambrian Mount Rogers Formation of southwestern Virginia includes thick units of massive conglomeratic mudstone Interpreted as tillite (Rankin, 1970; Blondeau and Lowe, 1972; Blondeau, 1975; Schwab, 1976). The tillite is composed of unsorted angular plutonic, metamorphic, volcanic, and sedimentary rock fragments enclosed within a matrix of sandy hematitic mudstone. The tillite is interbedded with arkosic sandstone, argillite, and conglomerate. Sedimentary structures and textures of these units suggest deposition by glaciers which protruded from land into a standing body of water as floating ice. Glacial drift was deposited in a large body of water, probably a lake, by piedmont glaciers which flowed from highland areas on the east and west sides of the basin. Unstratified tillite was deposited beneath melting floating ice, while arkosic sandstone and conglomerate accumulated as subaqueous outwash deposits near the submerged glacial ice front. Argillite was deposited in quiet-water areas of the lake. Five tillite sheets are correlated between three outcrops in the western part of the study area, based on stratigraphic position and textural characteristics. Upper member sedimentary rocks were deposited during a single, large-scale cycle of subaqueous glacial sedimentation punctuated by nine periods of ice advance. Distal varves, turbidites, and stratified tillite were deposited in the lower portion of the upper member. These lithofacies are conformably overlain in the upper portion of the member by proximal massive argillite, structureless sandstone, and unstratified tillite. This stratigraphic succession and overall upward coarsening of the unit suggest increasing proximality during deposition of the upper member of the Mount Rogers Formation

DETAILED GEOLOGIC MAPPING OF THE PARKSVILLE 7.5-MINUTE QUADRANGLE AND THE KINEMATICS OF EMPLACEMENT OF LARGE HORSES ALONG THE GREAT SMOKY FAULT, SOUTHEASTERN TENNESSEE

The Great Smoky fault is a major Alleghanian thrust fault in the southern Appalachians that separates the highly deformed and metamorphosed Blue Ridge to the east from the less deformed and unmetamorphosed Valley and Ridge to the west. The trace of the frontal Blue Ridge, as defined by the Great Smoky fault, displays a change in strike from ~010° to ~045° in or near the Parksville 7.5-minute quadrangle in southeastern Tennessee. This change in strike defines the southern arc of the Tennessee salient, which is a convex-to-the-foreland curve in the structural front of the southern Appalachians. Along the Great Smoky fault in the Parksville quadrangle are two large horses of Lower Cambrian Chilhowee Group rocks that could have affected the emplacement of the Great Smoky thrust sheet and caused the change in strike. Detailed geologic mapping of the Parksville quadrangle has shown that the northernmost horse is comprised of a section of Nebo Sandstone thrust over a section of Cochran Formation along a previously unmapped fault, with the intervening Nichols Shale removed. The southernmost horse is comprised of Cochran Formation and displays pervasive tectonic quartz veining. Analysis of hand samples and thin sections suggest that the horses were subjected to relatively low-temperature deformational conditions between approximately 300-400°C. Intense brittle and semi-ductile to ductile deformation occurs within the immediate vicinity of the Great Smoky fault zone but is not seen elsewhere in the horses, where primarily brittle deformation is observed. The lack of penetrative brittle and ductile deformation, the constraints on deformational temperatures, and the structural orientation of the Chilhowee Group horses suggests they were derived from the hanging wall of the Great Smoky thrust sheet. The emplacement of the horses likely did not affect the development of the southern limb of the Tennessee salient. Numerous horses occur along the Great Smoky fault, but no systematic change in geometry is observed where horses occur. Instead, the curvature of the Tennessee salient was likely controlled primarily by the irregular shape of the crystalline indenter, which, in the southern Appalachians, was the Blue Ridge-Piedmont megathrust sheet

Sedimentation and Stratigraphy of the Mount Rogers Formation, Virginia

The Mount Rogers Formation of southwestern Virginia is a thick, upper Precambrian sequence of interbedded conglomeratic mudstones, rhythmically layered argillites, arkosic sandstones and conglomerates, polymict conglomerates, and associated rhyolitic and latitic flows and pyroclastics. The conglomeratic mudstone consists of unsorted, angular to sub rounded grains, ranging in size from silt up to boulders one meter in diameter, enclosed within a fine-grained hematitic matrix or cement. The rhythmically layered argillite is made up of thin, alternating couplets of light, very fine-grained sandstone or siltstone grading upward into dark red argillite. Many of the couplets contain outsized exotic clasts which penetrate and deform underlying laminae and are overlain by undeformed laminae. Irregularly interbedded within the rhythmically layered argillite is a second population of thicker graded units composed of fine-grained sandstone containing shale rip-up clasts and exhibiting massive, flat laminated and small-scale cross-bedded zones which resemble Bouma intervals. The polymict conglomerate consists of rounded cobbles and pebbles of plutonic, metamorphic, volcanic and sedimentary rock embedded in a matrix of poorly-sorted coarse-grained arkose. The conglomerate is characterized by large-scale festoon cross-bedding, lateral impersistence of individual beds, and poor sorting. The sedimentary units of the Mount Rogers Formation are interpreted as a sequence of glacial and periglacial deposits including tillite (conglomeratic mudstone), glacio-lacustrine or glacio-marine varves (rhythmically layered argillite), interbedded turbidites, and glacio-fluvial debris (arkosic sandstone and conglomerate and polymict conglomerate). The sediment source included an older plutonic, metamorphic terrain and a penecontemporaneous rhyolitic volcanic complex

Structure of Blue Ridge thrust front, Tennessee, Southern Appalachians

An interpretation of a COCORP seismic reflection profile indicates that the Great Smoky thrust, cropping out in Southeast Tennessee, has a slip of about 140 km. Eight structure sections, drawn to the base of Paleozoic deformation, straddle the trace of the thrust and cover an area of about 12,000 square km. The sections show that the Great Smoky thrust cuts the most internal (southeasterly) structures of the Valley and Ridge thrust system, but was in place prior to movement of the Saltville fault in that system.The section suggests that several thrusts internal to the Great Smoky fault (Miller Cove, Dunn Creek, Brushy Mountain, and others) belong to a sled runner thrust complex (COCORP thrust system) similar to the Valley and Ridge. The basal detachment in this complex was the Great Smoky fault, and, in Northeast Tennessee, the Pulaski fault. The CGCORP thrust system differs from the more external Valley and Ridge thrust system in that it dismembers structures formed by polyphase, at least partly early Paleozoic, deformation. Pre-, syn-, and post- foliation structures are cut obliquely (map view) and discordantly (cross section) by elements of the COCORP thrust system along its external limit of outcrop. In the internal portion of the western Blue Ridge, relations of folds to COCORP thrusting are poorly documented, but several tectonic events are broadly synchronous with regional metamorphism. In particular, the Greenbrier fault, considered premetamorphic because it does not affect metamorphic isograds, postdates two phases of major folding. The dominant foliation in the area is axial planar to the earlier of these folding phases. In the Murphy area, however, the dominant and apparently earliest foliation is axial planar to a major structure which clearly folds isograds. A stratigraphic model for upper Precambrian to lowest Cambrian sediments in the Blue Ridge suggests that the Chilhowee, Walden Creek, Snowbird, and Great Smoky groups are partly facies equivalent strata. This model is based on a lower Ordovician or younger age of the Murphy marble and the assumption that the floor of the basin descends monotonically southeastward. Strike of facies boundaries, in palinspastic restoration, is east-west, or as much as 30 degrees more easterly than the strike of faults of the COCORP thrust system. In its restored position, the sedimentary wedge can be tied to a wedge of autochthonous sediments beneath east-central Georgia, evident in an interpretation of COCORP seismic reflection data. There is rough correspondence between the tapered edge of the sediments and a prominent gravity gradient. In thin-section, rocks of the Great Smoky Mountains and foothills, ranging from unmetamorphosed to the garnet zone of metamorphism, show less increase in grain size of layer silicates than expected. However, differences in character of both the main foliation in particular areas, and less obvious foliations, suggest increasing mobility of silica and other constituents and increasing dominance of lattice diffusion over grain-boundary diffusion in rocks deformed at higher temperature

THE CLIMATIC, BIOTIC AND TECTONIC EVOLUTION OF THE PALEOGENE RENOVA FORMATION OF SOUTHWESTERN MONTANA

The Renova Formation of southwestern Montana contains an important record of Paleogene floral, faunal, climate and tectonic change in the northern Rocky Mountains. The period between the end of the early Eocene and the early Oligocene (~49-32 Ma) was a time of rapid and far-reaching climate change. This period saw the end of global greenhouse climate and the establishment of icehouse conditions across the Earth. These changes led to profound alterations in both marine and terrestrial ecosystems. This study examines the late Eocene/early Oligocene history of the northern Rocky Mountains by means of an integrated study of the sedimentology, tectonics and fossil content of the Renova Formation. The first part of this study examines plant fossils found in the Renova Formation in order to examine changes in the composition of the vegetation across the late Eocene/ early Oligocene (E/O) boundary. Plant remains are an effective proxy for climate and are used to estimate multiple climatic parameters across the E/O boundary. The second part of this study examines the paleotopography and paleodrainage patterns of the basins which accumulated the Renova sediments. This is accomplished by a combination of sedimentary facies and detrital zircon analysis. The third part of this study examines the tectonic underpinnings of Paleogene southwestern Montana through a combination of geologic field work and geodynamic modeling. The results of this study indicate that a seasonal summer dry climate became established in the northern Rocky Mountains by early Oligocene time. This is indicated by the elimination of subtropical plant species, the establishment of dry-adapted species and by paleoclimate parameters calculated from leaf physiognomy. Geodynamic calculations and field data indicate that the Renova Formation was deposited in a series of sub-basins separated by relict paleotopography and inverted topography formed by contemporary lava flows. Normal faulting was not active until the middle Miocene initiation of regional extension. Accommodation space for the deposition of Renova sediments was formed primarily by differential erosion of pre-middle Eocene rocks. Climate change and influx rates of volcaniclastic sediment were also important controls on the evolution of the intermontane basins of southwestern Montana

Special External Effects on Fluvial System Evolution

Rivers are an excellent witness of the dynamics affecting Earth’s surface due to their sedimentary products and morphological expression, which may be considered as fluvial archives. Until now, the focus has been on evaluating the general impact of individual external factors. However, the importance of the specific environmental characteristics of these factors has become increasingly recognized, as highlighted in recent case studies. For example, the effects of regional climate, differentiated topography and vegetation, and frozen ground appear to play an essential role in the evolution of the fluvial system. Integration of such environmental conditions in the processes that were active within the complex fluvial system will open new perspectives in our progressive understanding of the evolution of landscape form, ecology, sediment fluxes, and hydrology of the system within the framework of the external drivers such as tectonics, general climate, and human activity. This is an appealing challenge that we wish to address in the present Special Issue under the aegis of the Fluvial Archives Group (FLAG)

Geomorphometry 2020. Conference Proceedings

Geomorphometry is the science of quantitative land surface analysis. It gathers various mathematical, statistical and image processing techniques to quantify morphological, hydrological, ecological and other aspects of a land surface. Common synonyms for geomorphometry are geomorphological analysis, terrain morphometry or terrain analysis and land surface analysis. The typical input to geomorphometric analysis is a square-grid representation of the land surface: a digital elevation (or land surface) model. The first Geomorphometry conference dates back to 2009 and it took place in Zürich, Switzerland. Subsequent events were in Redlands (California), Nánjīng (China), Poznan (Poland) and Boulder (Colorado), at about two years intervals. The International Society for Geomorphometry (ISG) and the Organizing Committee scheduled the sixth Geomorphometry conference in Perugia, Italy, June 2020. Worldwide safety measures dictated the event could not be held in presence, and we excluded the possibility to hold the conference remotely. Thus, we postponed the event by one year - it will be organized in June 2021, in Perugia, hosted by the Research Institute for Geo-Hydrological Protection of the Italian National Research Council (CNR IRPI) and the Department of Physics and Geology of the University of Perugia. One of the reasons why we postponed the conference, instead of canceling, was the encouraging number of submitted abstracts. Abstracts are actually short papers consisting of four pages, including figures and references, and they were peer-reviewed by the Scientific Committee of the conference. This book is a collection of the contributions revised by the authors after peer review. We grouped them in seven classes, as follows: • Data and methods (13 abstracts) • Geoheritage (6 abstracts) • Glacial processes (4 abstracts) • LIDAR and high resolution data (8 abstracts) • Morphotectonics (8 abstracts) • Natural hazards (12 abstracts) • Soil erosion and fluvial processes (16 abstracts) The 67 abstracts represent 80% of the initial contributions. The remaining ones were either not accepted after peer review or withdrawn by their Authors. Most of the contributions contain original material, and an extended version of a subset of them will be included in a special issue of a regular journal publication

Annual Report of the Board of Regents of the Smithsonian Institution, showing the operations, expenditures, and condition of the Institution for the year ending June 30, 1887

Annual Report of the Smithsonian Institution. [2581-2582] Research related to the American Indian

Annual Report of the Board of Regents of the Smithsonian Institution, showing the operations, expenditures, and condition of the Institution for the year ending June 30, 1887

Part 1 of 250-1Annual Report of the Smithsonian Institution. [2581-2582] Research related to the American Indian.1887-9