Our models show patterns reflecting local fault control on both shoreline regression and river deflections along the Atlantic Coastal Plain. In these models, maximum displacement is assumed to be at the center of a fault, and both uplifts and downwarps are assumed to be of sufficient magnitude to influence surface processes. Models show regional shoreline regression: (1A) without localized uplifts; (1B) with different rates of regional uplift at either end; (1C) without any localized uplifts but with a large river-dominated delta; (2A) with a fault parallel to the shoreline with seaward side down or (2B) with seaward side up; and (3) with a fault perpendicular to the shoreline. Model 1A has consistently spaced parallel shorelines and an absence of river deflections, such as characterizes most of the late Pleistocene coastal plain across Georgia. Model 1B has divergence of shorelines toward and deflection of rivers away from the end with greater uplift. Model 1C has seaward deflections of shorelines with spacing dependent upon rates of sediment influx and removal by coastal processes. Models 2A and 2B represent interruptions of model 1 patterns. Both produce a seaward deflection and wider spacing of younger shorelines on the uplifted side of the fault with associated river deflections toward the margins of the uplift. Both also produce a landward deflection and closer spacing of younger shorelines coupled with convergence of rivers toward the downdropped basin. Model 3 produces a seaward deflection and wider spacing of older shorelines across the uplift associated with river deflections toward the margins of the uplift on one side of the fault. On the other side, there is a landward deflection and narrower spacing of younger shorelines on the downdropped side of the fault where river deflections merge toward the lowest area. In model 3, shorelines are discontinuous and may be difficult to correlate across the fault, and fault length is constrained by resumption of model 1 shorelines seaward of the fault. Model 3 matches patterns in the vicinity of the 1886 Charleston earthquake, South Carolina, with a NW-trending fault of ~50 km length with the NE side up and uplift continuing since the early Pleistocene. Very similar patterns occur in the vicinity of Beaufort, South Carolina, and Wilmington, North Carolina, which suggest other NW-trending faults of comparable or greater length may be present near these localities. Model 2A matches patterns near the Okefenokee Swamp, which suggests that a 100-km-long, N-trending fault may border the east side of Trail Ridge near the Georgia-Florida state boundary. Model 2B was used by previous workers to explain zones of river anomalies in the Carolinas, but those anomalies do not match this model.

Intraplate earthquakes within the eastern United States represent brittle faulting in the upper crystalline crust at shallow to moderate depths. The premise—that intraplate seismicity in crystalline crust occurs along postorogenic brittle faults formed during extensional events—permits us to distinguish three large intraplate-earthquake domains in the eastern United States. These domains are: the Appalachian accreted terranes; the Grenvillian accreted terranes; and the midcontinent accreted terranes. These crystalline domains are separated by terrane boundaries, where metamorphic zones, formed during terrane accretion, seal off older brittle faults in an older terrane from any direct connection with newer brittle faults in a newer accreted terrane. Strain within each domain accumulates on preexisting fault zones formed during previous postorogenic extensional events. Although older faults in adjacent regions may be sealed off within independent terranes, extensional events that postdate accretion may generate younger brittle faults that cross the sealed boundaries. Thus, breaches created by younger migrating hotspots, failed rifts, and/or impact structures may provide local connecting zones across sealed boundaries. Detailed fracture studies within the Southern Appalachian accreted terranes, Triassic rift basins therein, and overlapping Cretaceous–Cenozoic passive-margin strata of the southern Atlantic Coastal Plain show that recurrent Mesozoic–Cenozoic brittle faulting: (1) is postorogenic and occurs along fracture sets formed during failed-to-successful Mesozoic rifting during the breakup of Pangea and opening of the Atlantic Ocean; (2) is not related to brittle reactivation of orogenic ductile shear zones or metamorphic fabrics; (3) is largely confined to accreted crystalline terranes in the Appalachians separated by metamorphosed zones, referred to previously, which are herein called sealed boundaries; (4) has younger, shorter fracture sets that are confined by older fault zones; and (5) formed in a temporal sequence of fracture sets that have a hierarchical ordering and scaling of recurrently active fault zones, with older, linked sets forming longer, more through-going fault zones, which bound large polygonal crustal blocks within accreted terranes. The second intraplate-earthquake domain is the Mesoproterozoic Grenville basement. Crystalline terranes of the Grenville orogen (ca. 1.2–0.9 Ga) were accreted during formation of the Rodinian supercontinent. The Rigolet phase (ca. 1.02–0.9 Ga) of the Grenville orogeny was characterized by a shift from contraction to NW-SE extension with development of core complexes (e.g., Adirondacks). Protracted cooling, continued NW-SE-extension, and passage of a hotspot (ca. 750–600 Ma) preceded the breakup of Rodinia and opening of the Iapetus Ocean at ca. 565 Ma. Thus, the Grenville orogen also contains a sequence of postorogenic brittle fracture sets, which subsequently formed recurrently active brittle fault zones. The third intraplate-earthquake domain contains the Archean–Mesoproterozoic orogenic belts in the midcontinent region, which are cut by brittle fracture sets related to: failed rifting events (e.g., ca. 1.1 Ga Midcontinent rift; Cambrian Southern Oklahoma aulacogen, Reelfoot rift, and Rough Creek graben); successful Triassic rifting and opening of the Gulf of Mexico; and Mid-Cretaceous passage of the Bermuda hotspot. Regional fracture sets formed during each of these postorogenic events and the temporal sequence of fracture sets determine the hierarchical ordering and scaling of recurrently active fault zones. Fault-plane solutions in major seismic zones within these three domains (Charleston, South Carolina, and central Virginia; east Tennessee and Giles County, Virginia; New Madrid and Wabash—Arkansas, Illinois, Kentucky, Missouri, Tennessee) are consistent with their occurrence along reactivated older fault zones.

Abstract Mesoproterozoic basement in the vicinity of Mount Rogers is characterized by considerable lithologic variability, including major map units composed of gneiss, amphibolite, migmatite, meta-quartz monzodiorite and various types of granitoid. SHRIMP U-Pb geochronology and field mapping indicate that basement units define four types of occurrences, including (1) xenoliths of ca. 1.33 to ≥1.18 Ga age, (2) an early magmatic suite including meta-granitoids of ca. 1185–1140 Ma age that enclose or locally intrude the xenoliths, (3) metasedimentary rocks represented by layered granofels and biotite schist whose protoliths were likely deposited on the older meta-granitoids, and (4) a late magmatic suite composed of younger, ca. 1075–1030 Ma intrusive rocks of variable chemical composition that intruded the older rocks. The magmatic protolith of granofels constituting part of a layered, map-scale xenolith crystallized at ca. 1327 Ma, indicating that the lithology represents the oldest, intact crust presently recognized in the southern Appalachians. SHRIMP U-Pb data indicate that periods of regional Mesoproterozoic metamorphism occurred at 1170–1140 and 1070–1020 Ma. The near synchroneity in timing of regional metamorphism and magmatism suggests that magmas were emplaced into crust that was likely at nearsolidus temperatures and that melts might have contributed to the regional heat budget. Much of the area is cut by numerous, generally east- to northeast-striking Paleozoic fault zones characterized by variable degrees of ductile deformation and recrystallization. These high-strain fault zones dismember the terrane, resulting in juxtaposition of units and transformation of basement lithologies to quartz- and mica-rich tectonites with protomylonitic and mylonitic textures. Mineral assemblages developed within such zones indicate that deformation and recrystallization likely occurred at greenschist-facies conditions at ca. 340 Ma.

Abstract The lower Congaree River Valley of central South Carolina is marked by a broad, asymmetrical, well-preserved, late Quaternary floodplain landscape that is home to the largest and best-preserved example of old-growth bottomland forest remaining in the southeastern United States. Vast areas of the floodplain are protected by Congaree National Park. Portions of the southern floodplain bluffs are protected by the South Carolina Department of Natural Resources Congaree Bluffs Heritage Preserve. This field guide presents a geological and geomorphological case study of this protected, forested floodplain landscape by highlighting relevant references and research results at several key field stops. Stops emphasize two distinct floodplain margins; stress the importance of plants to the geology; address anthropogenic and climatic influences on the system; and provide examples of floodplain depositional environments and processes that operate independently of the main river. Stop 1.1 is a brief overview of Congaree National Park. Stop 1.2 highlights the steep southern valley bluffs where the river has incised 46 m (150 ft) into upper Coastal Plain strata. Stop 1.3 highlights a unique road-cut exposure of Quaternary gravels. Stop 1.4 highlights the active Congaree River channel. Stop 1.5 highlights Late Cenozoic to Quaternary fluvial terraces north of the floodplain. Stop 1.6 highlights a groundwater rimswamp along the northern floodplain margin. Stop 2.1 involves a paddle on Cedar Creek, a major floodplain tributary. Stop 2.2 highlights Weston Lake, an anomalously large, well-defined oxbow lake. Stop 2.3 highlights one of many subtle, but stratigraphically and ecologically significant alluvial fans in the valley.

Abstract This one-day field trip highlights recent research into the late Holocene geomorphic evolution and land use history of Piedmont stream valleys near Raleigh, North Carolina. European settlers began building water-powered milldams in the eastern United States in the 1600s, and dam construction continued until the early twentieth century. At the same time, regional-scale land clearing associated with agriculture and development increased upland erosion rates 50–400 times above long-term geologic rates. Much of the eroded sediment was subsequently aggraded on floodplains and impounded behind milldams. This trapped "legacy" sediment, commonly mistaken for natural floodplain deposition, has gone largely unrecognized until recently. This study focuses upon 1st to 4th order streams in W.B. Umstead State Park that drain into the Neuse River basin. There are seven water-powered milldam locations within the park and adjacent areas. Geomorphic mapping demonstrates that upland soil erosion and valley bottom sediment aggradation was substantial following European-American land acquisition and their conversion of large amounts of forest land for agricultural purposes. We observe three distinct sedimentary units in stream bank exposures that are corroborated by 14 C dating. Pre-European sediments range from ca. 4400–250 yr B.P. and consist of quartz-rich axial stream gravels and off-channel organic rich clays. Two legacy sediment units are differentiable; pre and post-dam, and range in age from ca. 300–100 yr B.P. The pre-dam sediments consist primarily of fluvial sands, and are interpreted as channel aggradation in response to soil erosion from upland land clearing prior to dam construction. Post-dam sediments are distinguished by finer grain size and sedimentology consistent with slackwater deposition, including sandy "event" layers, interpreted to be the result of large floods into the former mill ponds. Stream bank magnetic susceptibility (MS) measurements exhibit large and consistent increases at and above the pre-European-legacy sediment contact, suggesting that MS is a suitable proxy for legacy sediment identification along North Carolina Piedmont streams. Estimates of aggraded legacy sediment from two stream reaches in Umstead State Park indicate that the volume of eroded upland soils is approximately balanced by valley bottom sediment aggradation, and that area-averaged depth of upland soil loss was equivalent to 3–15 cm across this part of the Piedmont. We evaluate the current impact of legacy sediment erosion on stream water quality by capturing the total suspended sediment load (TSS) during discharge events using ISCO samplers at 5 sites on Reedy and Richland Creek. We document a TSS increase as water passes through reaches containing milldam deposits. This suggests that modern stream water impairment in the Piedmont may result where milldams were constructed and legacy sediments impounded. The field trip concludes by examining an active beaver (Castor canadensis) pond–wetland meadow complex above the historic Yates Mill pond. Beavers may prove to be valuable assets in the restoration of Piedmont stream systems still suffering from centuries of poor land and soil management.

Abstract The New Madrid seismic zone of the central Mississippi River valley is the most seismically active area of the United States east of the Rocky Mountains. Most noted for its very large earthquakes during the winter months of 1811–1812 and its earthquake recurrence interval of ∼500 years for the past 1200 years, concern about future damaging earthquakes requires continued appraisal of that threat. Although the magnitudes of these earthquakes continue to be debated, we do know that major landform changes occurred during the four major historical earthquakes—three main shocks and one very large aftershock. These changes include landslides along the Chickasaw Bluffs in western Kentucky and Tennessee, formation of Reelfoot Lake in Tennessee, subsidence of the sunklands of northeastern Arkansas, uplift of the Lake County uplift with its eastern boundary being the Reelfoot scarp in northwestern Tennessee and southwestern Kentucky, and extensive liquefaction in northeastern Arkansas, southeastern Missouri, and western Tennessee. In this field trip we will visit and discuss the Lake County uplift, Reelfoot scarp, Reelfoot Lake, the Chickasaw Bluffs and their underlying stratigraphy, and liquefaction deposits in northeastern Arkansas.

Abstract In 1886, a large earthquake (∼M6.9–M7.3) rocked the Summerville-Charleston South Carolina area along the southeastern coast of North America. The largest east coast earthquake in North America, the earthquake caused massive damage to the cities and left ∼100 people dead. No surface rupture has ever been located; however, ongoing seismicity and damage from the 1886 earthquake has helped scientists to locate the active faults at depth and to identify potential surface offsets. The first day of the field trip will look at the damage from the earthquake as a means of understanding more about the mechanics of the earthquake. As the field trip moves into downtown Charleston, the damage will be examined as a proxy for how earthquakes cause buildings to fail and the type of damage a future earthquake could cause. The ongoing seismic activity along the suspected causal faults suggests that the earthquake risk in the Summerville-Charleston area remains high, and so the second day of the field trip will focus on the potential effects of a moderate to large earthquake in the region of the 1886 earthquake. One of the unique features of the Charleston-Summerville area is the high potential for widespread liquefaction and damage to the many bridges in the area. Therefore, Day 2 will focus on the potential for damage from a major earthquake on bridges and highly liquefiable sites by visiting a bridgeport area and then a barrier island. The visit to the barrier island highlights one of the main problems in Charleston in the event of an earthquake, the isolation of communities, with over 720 bridges and many more culverts in the area it is expected that people will be isolated in small communities for long periods of time.

Abstract The Inner Piedmont extends from North Carolina to Alabama and comprises the Neoacadian (360–345 Ma) orogenic core of the southern Appalachian orogen. Bordered to west by the Blue Ridge and the exotic Carolina superterrane to the east, the Inner Piedmont is cored by an extensive region of migmatitic, sillimanite-grade rocks. It is a composite of the peri-Laurentian Tugaloo terrane and mixed Laurentian and peri-Gondwanan affinity Cat Square terrane, which are exposed in several gentle-dipping thrust sheets (nappes). The Cat Square terrane consists of Late Silurian to Early Devonian pelitic schist and metagraywacke intruded by several Devonian to Mississippian peraluminous granitoids, and juxtaposed against the Tugaloo terrane by the Brindle Creek fault. This field trip through the North Carolina Inner Piedmont will examine the lithostratigraphies of the Tugaloo and Cat Square terranes, deformation associated with Brindle Creek fault, Devonian-Mississippian granitoids and charnockite of the Cat Square terrane, pervasive amphibolite-grade Devonian-Mississippian (Neoacadian) deformation and metamorphism throughout the Inner Piedmont, and existence of large crystalline thrust sheets in the Inner Piedmont. Consistent with field observations, geochronology and other data, we have hypothesized that the Carolina superterrane collided obliquely with Laurentia near the Pennsylvania embayment during the Devonian, overrode the Cat Square terrane and Laurentian margin, and squeezed the Inner Piedmont out to the west and southwest as an orogenic channel buttressed against the footwall of the Brevard fault zone.

Abstract The focus of this field trip is the complex lithologic, metamorphic and structural transition between high-grade infrastructural and low-grade suprastructural terranes that define the accreted peri-Gondwanan Neoproterozoic-Cambrian Carolina Zone, an island-arc superterrane in the north-central Piedmont of North Carolina. This transition is now exposed across a metamorphic suite of amphibolite facies layered gneiss plus kyanite-sillimanite zone pelitic schist, and another metamorphic suite of greenschist facies mylonitic and phyllonitic metagranitoids and their undeformed equivalents. A variety of mineral assemblages, fabric elements, and structures within the transition zone may be linked into a progressive sequence recording (1) the transpressional buildup of an Alleghanian collision zone between Laurentia, the Carolina Zone, and Gondwana during Pangean continental amalgamation, and (2) its extensional collapse during the Permo-Triassic through Jurassic rifting and breakup of Pangea. We will observe the effects of Alleghanian ductile strain superposed on this infrastructural-suprastructural terrane transition, including the interplay between dextral transpression and the generation of syn- to post-kinematic granitic plutons. Metamorphosed volcanogenic and syn-kinematic granitoid rocks record the effects of ductile dextral-slip deformation associated with at least four major fault zones. These fault zones are combined as the Nutbush Creek–Lake Gordon fault system, an integral member of the Eastern Piedmont fault system. Finally, the trip highlights the ductile-brittle effects of Late Permian to Triassic normal-slip faulting, uplift and rift sedimentation in the northern Durham sub-basin of the Triassic Deep River rift basin, as well as crosscutting Jurassic intrusive rocks.

Abstract The allochthonous Talladega belt of eastern-northeastern Alabama and northwestern Georgia is a northeast striking, fault bounded block of lower greenschist facies metasedimentary and metaigneous rocks that formed along the margin of Laurentia at or outboard of the seaward edge of the Alabama promontory. Bounded by metamorphic rocks of the higher grade Neoproterozoic(?) to Carboniferous eastern Blue Ridge on the southeast and unmetamorphosed to anchimetamorphic Paleozoic rocks of the Appalachian foreland on the northwest, the Talladega belt includes shelf facies rocks of the latest Neoproterozoic/earliest Cambrian Kahatchee Mountain Group, Cambrian-Ordovician Sylacauga Marble Group, and the latest Silurian(?) to uppermost Devonian/earliest Mississippian Talladega Group. Along the southeastern flank of these metasedimentary sequences, a Middle Ordovician back-arc terrane (Hillabee Greenstone) was tectonically emplaced along a cryptic pre-metamorphic thrust fault (Hillabee thrust) and subsequently dismembered with units of the upper Talladega Group along the post-metamorphic Hollins Line fault system. Importantly, strata within the Talladega belt are critical for understanding the tectonic evolution of the southern Appalachian orogen when coupled with the geologic history of adjacent terranes. Rocks of the lower Talladega Group, the Lay Dam Formation, suggest latest Silurian–earliest Devonian tectonism that is only now being recognized in other areas of the southern Appalachians. Additionally, correlation between the Middle Ordovician Hillabee Greenstone and similar bimodal metavolcanic suites in the Alabama eastern Blue Ridge and equivalent Dahlonega Gold belt of Georgia and North Carolina suggests the presence of an extensive back-arc volcanic system on the Laurentian plate just outboard of the continental margin during the Ordovician and has significant implications for models of southern Appalachian Taconic orogenesis.

Abstract The central Piedmont of South Carolina includes two terranes derived from Neoproterozoic peri-Gondwanan arcs and one that preserves the Cambrian Series 2–Series 3 Carolinian Rheic rift-drift sequence. These are the Charlotte, Silverstreet and Kings Mountain terranes. The central Piedmont shear zone juxtaposes each of these terranes against the Late Silurian Cat Square paragneiss terrane. The Kings Mountain terrane is composed of meta-epiclastic rocks with distinctive metaconglomerate horizons, manganiferous formation, meta-sandstones, and dolomitic marbles. One of the lower metaconglomerate horizons yields detrital zircons of latest Middle Cambrian age. This stratigraphy is interpreted to record the Rheic rift-drift sequence on the trailing edge of an Ediacaran-Cambrian arc terrane as it pulled away from the Amazonian craton in Middle Cambrian–Furongian time. The Charlotte terrane records magmatic activity from before 579 ± 4 until ∼535 ± 4 Ma. Mafic-ultramafic zoned intrusive complexes intruded mafic-ultramafic volcanic piles. Ultramafic dikes cut the volcanic rocks and are interpreted as feeders to stratigraphically higher levels of volcanism. These mafic to ultramafic rocks record arc rifting resulting from subduction of a spreading ridge or bathymetric high. These rocks were metamorphosed to amphibolite facies at about the time of the Cambrian–Precambrian transition. The Silverstreet terrane preserves relict medium temperature eclogites and high-pressure granulites in the lower plate (Charlotte terrane) of an arc-arc collision. Relict high-pressure assemblages record 1.4 GPa, 650–730 °C conditions. High-pressure mineralogy and textures are best preserved in the cores of boudins derived from dikes with Ti-V ratios of 20–50 (i.e., MORB). High-pressure metamorphism may have occurred in Ediacaran-Cambrian time, and must have occurred prior to the intrusion of the 414 ± 8 Ma Newberry granite. The Cat Square basin contains detrital zircons as young as 430 Ma, accepted detritus from both Laurentia and Carolinia, and so is interpreted as a successor basin. The Cat Square terrane underwent peak (upper amphibolite-granulite) metamorphic conditions at the time of the Devonian–Mississippian transition while it was at the latitude of the New York Promontory. The peri-Laurentian-Carolinian suture is either buried under the Blue Ridge Piedmont thrust sheet or was thrust up and eroded away. The central Piedmont shear zone is a younger feature, no older than Visean.

Abstract The central Virginia Piedmont is underlain by complex igneous and metamorphic rocks, including: Paleozoic, Neoproterozoic, and Mesoproterozoic rocks of the suspect Goochland terrane; Early Paleozoic rocks of the suspect Chopawamsic arc terrane; Mid-Paleozoic successor basin deposits; and a suite of Taconic and Alleghanian plutons. Terranes are juxtaposed along a network of Late Paleozoic dextrally transpressive high-strain zones. The origin and significance of both the Goochland and Chopawamsic terranes remain a source of debate. The central Virginia Piedmont includes a distinct suite of commercial-grade mineral deposits including rutile-rich anorthosite, pegmatite, kyanite, and slate. The widely felt 2011 Virginia earthquake (M = 5.8) occurred along an unrecognized fault in the central Virginia seismic zone and demonstrates that old Appalachian structures are still active in eastern North America's modern stress field.

Abstract In latest Devonian time, the collision between Avalonia, the New York promontory and Carolina terrane under the impact of Gondwana, generated an orogeny that began in New England and migrated southward in time. Once thought to be the fourth tectophase of the Acadian orogeny, this event is now called the Neoacadian orogeny. Active deformational loading during the event initially produced the Sunbury black-shale basin, whereas subsequent relaxational phases produced the Borden-Grainger-Price-Pocono and Pennington–Mauch Chunk clastic wedges, which largely reflect the dextral transpressional docking of the Carolina terrane against the Virginia promontory and points southward. The Sunbury black-shale basin and the infilling clastic wedges are among the thickest and most extensive in the Appalachian foreland basin. This trip will demonstrate differences in basinal black-shale and deltaic infilling of the foreland basin, both in more active, proximal and in more distal, sediment-starved parts of the basin. In particular, we will examine relationships between sedimentation and tectonism in the Early-Middle Mississippian Sunbury/Borden/Grainger/Fort Payne delta/basin system in the western Appalachian Basin during the Neoacadian Orogeny. We will emphasize the interrelated aspects of delta sedimentation, basin starvation, and mud-mound genesis on and near the ancient Borden-Grainger delta front. Temporal constraints are provided by the underlying Devonian-Mississippian black shales and by the widespread Floyds Knob Bed/zone, a dated glauconite/phosphorite interval that occurs across the distal delta/basin complex.