ABSTRACT Data from 33 locations were utilized in a stratigraphic study of the Early Mississippian Grainger Formation and related units in northeast Tennessee. Isopach maps, stratigraphic cross sections, and lithologic trends indicate the Grainger Formation was deposited in four deltaic lobes: Monroe, Rock Haven, Hancock, and Grainger-Borden. Each is in a separate outcrop belt: Chilhowie Mountain, Clinch Mountain, Newman Ridge, and Cumberland Mountain. The Monroe lobe is the eastern and southernmost of the lobes. Within it, the Grainger Formation is thicker and coarser than in the other locales. It is underlain by gray and black shale; the gray shale is a probable nearshore gray version of the usually greenish Maury Formation. The Greasy Cove Formation, a heterogeneous unit of sandstone, shale, red beds, and limestone, overlies the Grainger Formation and occupies the stratigraphic position of the Maccrady Formation and Newman Limestone in outcrop belts to the northwest. The Greasy Cove Formation is recognized only in the Monroe lobe. In the Rock Haven lobe, both the Grainger Formation and Chattanooga Shale are divisible into mappable members. The Chattanooga Shale consists of an upper Big Stone Gap Member, a middle Brallier Member, and a lower Millboro Member. The Chattanooga Shale locally is 600+ m thick. The Grainger Formation in the Rock Haven lobe is divisible into three newly named members: an upper Hayters Sandstone member, a middle Greendale member, and a basal Bean Station member. The Alumwell glauconite zone, within the upper part of the Greendale member, is also new. The center of the zone approximates a time line and is a key stratigraphic horizon. All Grainger members and the Alumwell glauconite are traceable into the Price Formation of southwest Virginia. In the Rock Haven lobe, the Chattanooga Shale, Grainger Formation, and Maccrady Formation were deposited in a subsiding trough; subsidence began in the Givetian and perhaps in the Eifelian, caused by a migrating peripheral bulge generated by Neoacadian deformation in the Carolina Piedmont. Highlands created by the deformation were the eastern sediment source for the Chattanooga, Grainger, and Maccrady formations in this lobe. Sediment for the Hancock and Grainger-Borden lobes originated from northerly sources. In the Hancock lobe, the Chattanooga Shale and Grainger Formation are thinner, and the Grainger Formation has increased shale content to the south. Paleocurrent data indicate a north-south current flow. The Hancock lobe is likely a southern extension of the Price delta system in southwest Virginia. The Grainger-Borden lobe is the southern terminus of the Borden delta system of Kentucky. Both the Chattanooga Shale and Grainger Formation thin to the south and southeast. The Floyds Knob glauconite bed was deposited during a pause in sediment delivery and separates the Fort Payne Chert from the underlying Grainger Formation as a distinct sedimentary unit. The Fort Payne Chert overlaps the Grainger Formation from a deeper southern basin where the dolostone and chert have little or no interbedded shale. The overlap does not interfinger with the Grainger Formation. The Fort Payne Chert becomes thinner as it progresses northward, finally passing into the Muldraugh Formation in Kentucky. It also made a minor incursion eastward into the western margin of the Hancock lobe, where some chert(y) beds occur at the Maccrady position.

Abstract Welcome to the Appalachian landscape! Our field trip begins with a journey across Fall Zone (Fig. 1 ), named for the falls and rapids on streams flowing from the consolidated rocks of the Appalachians onto the unconsolidated sediments of the Coastal Plain. The eastern U.S. urban centers are aligned along the Fall Zone, the upstream limit of navigation. Typically, the rocks west of the Fall Zone are part of the Piedmont province. This province exposes the metamorphic core of the Appalachian Mountains exhumed by both tectonics and erosion. At least four major phases of deformation are preserved in Piedmont rocks, three Paleozoic convergent events that closed Iapetus, followed by Mesozoic extension that opened the Atlantic Ocean. A record of Cretaceous to Quaternary exhumation of the Appalachians is preserved as Coastal Plain sediments. Late Triassic and Jurassic erosion is preserved in the syn-extensional fault basins, such as the Newark basin, or is buried beneath Coastal Plain sediments (Fig. 1 ). The trip proceeds northwest across the Fall Zone and Piedmont and into the Newark basin. Late Triassic and Jurassic fluvial red sandstone, lacustrine gray shale, and black basalt were deposited in this basin. The Newark basin is separated from the Blue Ridge by a down to the east normal fault that locally has contemporary microseismicity. The Blue Ridge represents a great thrust sheet that was emplaced from the southeast during the Alleghenian orogeny (Permian). The summits of the Blue Ridge are commonly broad and accordant. Davis (1889) projected that accordance westward to the summits of the Ridge and Valley to define his highest and oldest peneplain—the Schooley peneplain. North and west of the Blue Ridge is the Great Valley Section of the Ridge and Valley Province (Fig. 1 ). Where we cross the Great Valley at Harrisburg, it is called the Cumberland and Lebanon valleys. This section is underlain by lower Paleozoic carbonate, shale, and slate folded and faulted during the lower Paleozoic Taconic orogeny. The prominent ridge on the west flank of the Great Valley is Blue or Kittatinny Ridge. It is the first ridge of the Ridge and Valley Province; the folded and faulted sedimentary rocks of the Appalachian foreland basin, deformed during the Alleghenian orogeny. Drainage during most of the Paleozoic was to the northwest, bringing detritus into the Appalachian foreland basin. The drainage reversed with the opening of the Atlantic Ocean and southeast-flowing streams established courses transverse to the strike of resistant rocks, like the Silurian Tuscarora Sandstone holding up Blue Mountain. West and north of the Ridge and Valley is the Allegheny Plateau, that part of the Appalachian foreland that was only gently deformed during Alleghenian shortening. Our trip will traverse that part of the plateau called the Pocono Plateau which is underlain by Devonian to Penn-sylvanian sandstone. At the conclusion of our trip, we will reverse our transverse of the Appalachians by traveling from the Pocono Plateau to the Ridge and Valley, to the Great Valley, to the Newark Basin, to the Piedmont, and then to one of the great Fall Zone cities—Philadelphia—via the Lehigh and Schuylkill rivers.

Abstract Detailed geologic mapping and new SHRIMP (sensitive high-resolution ion microprobe) U-Pb zircon, Ar/Ar, Lu-Hf, 14 C, luminescence (optically stimulated), thermochronology (fission-track), and palynology reveal the complex Mesoproterozoic to Quaternary geology along the ~350 km length of the Blue Ridge Parkway in Virginia. Traversing the boundary of the central and southern Appalachians, rocks along the parkway showcase the transition from the para-autochthonous Blue Ridge anticlinorium of northern and central Virginia to the allochthonous eastern Blue Ridge in southern Virginia. From mile post (MP) 0 near Waynesboro, Virginia, to ~MP 124 at Roanoke, the parkway crosses the unconformable to faulted boundary between Mesoproterozoic basement in the core of the Blue Ridge anticlinorium and Neoproterozoic to Cambrian metasedimentary and metavolcanic cover rocks on the western limb of the structure. Mesoproterozoic basement rocks comprise two groups based on SHRIMP U-Pb zircon geochronology: Group I rocks (1.2-1.14 Ga) are strongly foliated orthogneisses, and Group II rocks (1.08-1.00 Ga) are granitoids that mostly lack obvious Mesoproterozoic deformational features. Neoproterozoic to Cambrian cover rocks on the west limb of the anticlinorium include the Swift Run and Catoctin Formations, and constituent formations of the Chilhowee Group. These rocks unconformably overlie basement, or abut basement along steep reverse faults. Rocks of the Chilhowee Group are juxtaposed against Cambrian rocks of the Valley and Ridge province along southeast- and northwest-dipping, high-angle reverse faults. South of the James River (MP 64), Chilhowee Group and basement rocks occupy the hanging wall of the nearly flat-lying Blue Ridge thrust fault and associated splays. South of the Red Valley high-strain zone (MP 144.5), the parkway crosses into the wholly allochthonous eastern Blue Ridge, comprising metasedimentary and meta-igneous rocks assigned to the Wills Ridge, Ashe, and Alligator Back Formations. These rocks are bound by numerous faults, including the Rock Castle Creek fault that separates Ashe Formation rocks from Alligator Back Formation rocks in the core of the Ararat River synclinorium. The lack of unequivocal paleontologic or geochronologic ages for any of these rock sequences, combined with fundamental and conflicting differences in tectonogenetic models, compound the problem of regional correlation with Blue Ridge cover rocks to the north. The geologic transition from the central to southern Appalachians is also marked by a profound change in landscape and surficial deposits. In central Virginia, the Blue Ridge consists of narrow ridges that are held up by resistant but contrasting basement and cover lithologies. These ridges have shed eroded material from their crests to the base of the mountain fronts in the form of talus slopes, debris flows, and alluvial-colluvial fans for perhaps 10 m.y. South of Roanoke, however, ridges transition into a broad hilly plateau, flanked on the east by the Blue Ridge escarpment and the eastern Continental Divide. Here, deposits of rounded pebbles, cobbles, and boulders preserve remnants of ancestral west-flowing drainage systems. Both bedrock and surficial geologic processes provide an array of economic deposits along the length of the Blue Ridge Parkway corridor in Virginia, including base and precious metals and industrial minerals. However, common stone was the most important commodity for creating the Blue Ridge Parkway, which yielded building stone for overlooks and tunnels, or crushed stone for road base and pavement.

ABSTRACT The Columbia River Gorge is the Columbia River’s long-held yet evolving passage through the volcanic arc of the Cascade Range. The globally unique setting of a continental-scale river bisecting an active volcanic arc at the leading edge of a major plate boundary creates a remarkable setting where dynamic volcanic and tectonic processes interact with diverse and energetic fluvial processes. This three-day field trip explores several elements of the gorge and its remarkable geologic history—cast here as a contest between regional tectonic and volcanic processes building and displacing landscapes, and the relentless power of the Columbia River striving to maintain a smooth passage to the sea. DEDICATION Dedicated to Russell C. Evarts (7 April 1947–11 July 2017) and his contributions to Pacific Northwest geology. Russ Evarts devoted most of his 30-year career with the U.S. Geological Survey to geologic mapping of Oregon and Washington. His thorough geologic mapping of the near-vertical terrain of the western Columbia River Gorge underpins much of what is reported in this guide and continues to inspire our studies of the geology of the Pacific Northwest.

Abstract Examination of key outcrops in the eastern Blue Ridge in southern Virginia and northwestern North Carolina is used to evaluate existing stratigraphic and structural models. Recent detailed mapping along the Blue Ridge Parkway and the eastern flank of the Mount Rogers massif provides the opportunity to (1) evaluate legacy data and interpretations and (2) formulate new ideas for regional correlation of eastern Blue Ridge geology. Lynchburg Group rocks in central Virginia (metagraywacke, quartzite, graphitic schist, amphibolite, and ultramafic rocks) carry southward along strike where they transition with other units. Wills Ridge Formation consists of graphitic schist, metagraywacke, and metaconglomerate, and marks the western boundary of the eastern Blue Ridge. The Ashe Formation consists of conglomeratic metagraywacke in southern Virginia, and mica gneiss, mica schist, and ultramafic rocks in North Carolina. The overlying Alligator Back Formation shows characteristic compositional pin-striped layers in mica gneiss, schist, and amphibolite. The contact between eastern Blue Ridge stratified rocks above Mesoproterozoic basement rocks is mostly faulted (Gossan Lead and Red Valley). The Callaway fault juxtaposes Ashe and Lynchburg rocks above Wills Ridge Formation. Alligator Back Formation rocks overlie Ashe and Lynchburg rocks along the Rock Castle Creek fault, which juxtaposes rocks of different metamorphism. The fault separates major structural domains: rocks with one penetrative foliation in the footwall, and pin-striped recrystallized compositional layering, superposed penetrative foliations, and cleavage characterize the hanging wall. These relationships are ambiguous along strike to the southwest, where the Ashe and Alligator Back formations are recrystallized at higher metamorphic grades.

ABSTRACT The southern Appalachian orogen is a Paleozoic accretionary-collisional orogen that formed as the result of three Paleozoic orogenies, Taconic, Acadian and Neoacadian, and Alleghanian orogenies. The Blue Ridge–Piedmont megathrust sheet exposes various crystalline terranes of the Blue Ridge and Inner Piedmont that record the different effects of these orogenies. The western Blue Ridge is the Neoproterozoic to Ordovician Laurentian margin. Constructed on Mesoproterozoic basement, 1.2–1.0 Ga, the western Blue Ridge transitions from two rifting events at ca. 750 Ma and ca. 565 Ma to an Early Cambrian passive margin and then carbonate bank. The Hayesville fault marks the Taconic suture and separates the western Blue Ridge from distal peri-Laurentian terranes of the central and eastern Blue Ridge, which are the Cartoogechaye, Cowrock, Dahlonega gold belt, and Tugaloo terranes. The central and eastern Blue Ridge terranes are dominantly clastic in composition, intruded by Ordovician to Mississippian granitoids, and contain ultramafic and mafic rocks, suggesting deposition on oceanic crust. These terranes accreted to the western Blue Ridge during the Taconic orogeny at 462–448 Ma, resulting in metamorphism dated with SHRIMP (sensitive high-resolution ion microprobe) U-Pb ages of metamorphic zircon. The Inner Piedmont, which is separated from the Blue Ridge by the Brevard fault zone, experienced upper amphibolite, sillimanite I and higher-grade ­metamorphism during the Acadian and Neoacadian orogenies, 395–345 Ma. These events also affected the eastern Blue Ridge, and parts of the western Blue Ridge. The Acadian and Neoacadian orogeny is the result of the oblique collision and accretion of the peri-Gondwanan Carolina superterrane overriding the Inner Piedmont. During this collision, the Inner Piedmont was a forced mid-crustal orogenic channel that flowed NW-, W-, and SW-directed from underneath the Carolina superterrane. The Alleghanian orogeny thrust these terranes northwestward as part of the Blue Ridge–Piedmont megathrust sheet during the collision of Gondwana (Africa) and the formation of Pangea.

Abstract The San Juan volcanic field comprises 25,000 km 2 of intermediate composition mid-Tertiary volcanic rocks and dacitic to rhyolitic calderas including the San Juan-Uncompahgre and La Garita caldera-forming super-volcanoes. The region is famous for the geological, ecological, hydrological, archeological, and climatological diversity. These characteristics supported ancestral Puebloan populations. The area is also important for its mineral wealth that once fueled local economic vitality. Today, mitigating and/or investigating the impacts of mining and establishing the region as a climate base station are the focuses of ongoing research. Studies include advanced water treatment, the acid neutralizing capacity (ANC) of propylitic bedrock for use in mine-lands cleanup, and the use of soil amendments including biochar from beetle-kill pines. Biochar aids soil productivity and revegetation by incorporation into soils to improve moisture retention, reduce erosion, and support the natural terrestrial carbon sequestration (NTS) potential of volcanic soils to help offset atmospheric CO 2 emissions. This field trip will examine the volcano-tectonic and cultural history of the San Juan volcanic field as well as its geologic structures, economic mineral deposits and impacts, recent mitigation measures, and associated climate research. Field trip stops will include a visit to (1) the Summitville Superfund site to explore quartz alunite-Au mineralization, and associated alteration and new water-quality mitigation strategies; (2) the historic Creede epithermal-polymetallic-vein district with remarkably preserved resurgent calderas, keystone-graben, and moat sediments; (3) the historic mining town of Silverton located in the nested San Juan-Silverton caldera complex that exhibits base-metal Au-Ag mineralization; and (4) the site of ANC and NTS studies. En route back to Denver, we will traverse Grand Mesa, a high NTS area with Neogene basalt-derived soils and will enjoy a soak in the geothermal waters of the Aspen anomaly at Glenwood Springs.

Abstract Since the opening of the Space Age, images from spacecraft have enabled us to map the surfaces of all the rocky planets and satellites in the Solar System, thus transforming them from astronomical to geological objects. This progression of geology from being a strictly Earth-centred science to one that is planetary-wide has provided us with a wealth of information on the evolutionary histories of other bodies and has supplied valuable new insights on the Earth itself. We have learned, for example, that the Earth–Moon system most likely formed as a result of a collision in space between the protoearth and a large impactor, and that the Moon subsequently accreted largely from debris of Earth's mantle. The airless, waterless Moon still preserves a record of the impact events that have scarred its surface from the time its crust first formed. The much larger, volcanic Earth underwent a similar bombardment but most of the evidence was lost during the earliest 550 million years or so that elapsed before its first surviving systems of crustal rocks formed. Therefore, we decipher Earth's earliest history by investigating the record on the Moon. Lunar samples collected by the Apollo astronauts of the USA and the robotic Luna missions of the former USSR linked the Earth and Moon by their oxygen isotopic compositions and enabled us to construct a timescale of lunar events keyed to dated samples. They also permitted us to identify certain meteorites as fragments of the lunar crust that were projected to the Earth by impacts on the Moon. Similarly, analyses of the Martian surface soils and atmosphere by the Viking and Pathfinder missions led to the identification of meteorite fragments ejected by hypervelocity impacts on Mars. Images of Mars displayed land-forms wrought in the past by voluminous floodwaters, similar to those of the long-controversial Channeled Scablands of Washington State, USA. The record on Mars confirmed catastrophic flooding as a significant geomorphic process on at least one other planet. The first views of the Earth photographed by the crew of Apollo 8 gave us the concept of 'Spaceship Earth' and heightened international concern for protection of the global environment.