ABSTRACT A local clay lens up to 60 cm thick in the Eocene Castle Hayne Limestone at the abandoned Fussell Quarry, Duplin County, North Carolina, is identified as a bentonite. It is composed of authigenic smectite with sparse euhedral biotite and apatite. Scanning electron microscope examination shows that the bentonite consists of relic bubble-wall shards altered to smectite. Smectitic columnules, rod-shaped casts of elongate pipe vesicles in pumice fragments derived from early dissolution of nearby small glass shards, also occur. This association is considered diagnostic of a silicic air-fall ash. K-Ar and Rb-Sr biotite dates from the bentonite are 46.2 ± 1.8 Ma and 45.7 ± 0.7 Ma, respectively, and a fission-track age of apatite is 51.0 ± 2.0 Ma; this later date is considered to be incorrect. Biotite compositions determined from electron microprobe analyses on 100 crystals suggest derivation from a single volcanic source no more than 4000 km from the bentonite. Possible sources of the ash include Bermuda; Highland County, Virginia; and the Caribbean; however, because of distance, prevailing wind direction, and similarity in age and composition, the volcanic swarm in Highland County, Virginia, is the suggested source.

Abstract Noble gas isotopes, major element isotopes, and gas composition were obtained from the shut-in Butler #3 (API 32-105-00008) and Simpson #1 (API 32-105-00007) wells, drilled in 1998, and sample gas from the Cumnock Formation of Late Norian age. This is the first gas chemistry compilation of these wells. The wells’ gas, sampled in 2009 and in 2014, had a strong “fruity” light petroleum odor, a visible condensate plume when the wells were flowed, and are in the oil and wet gas window. Shutin well pressures were ~900 psi (Butler #3), and ~200 psi (Simpson #1); both had a substantial initial gas flow. Limited data are from the 1982 Dummitt-Palmer #1 CBM well (API 32-105-00002), now plugged and abandoned. Helium concentrations were ~0.20% to 0.24% from the noble gas analysis, neon ranged from 0.11 to 0.04 ppm, and argon was approximately 33 ppm. The measured noble gas composition contains very low atmospheric contamination with helium isotopes (0.07 R/R A ) clearly defined by a crustal origin, while neon and krypton and are mainly attributed to atmospheric origin ( 20 Ne/ 22 Ne ~9.8, 86 Kr/ 84 Kr ~0.3). Argon isotopes are mixed between crustal and atmospheric origins with 40 Ar/ 36 Ar values ~ 418 to 520. The F 20 Ne/ 36 Ar (~0.9 to 2.6), F 84 Kr/ 36 Ar (~0.8) and F 132 Xe/ 36 Ar (0.6-0.7) in the gas show enrichment in the light isotope associated with multi-stage fractionation processes with gas and fluid interaction. The methane content (range ~58 to 64%) is inverse to the nitrogen content from denitrification of very thin ammonium-bearing units (also rich in oil), and likely from illite in overlying strata.

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.

Dam construction and its impact on downstream fluvial processes may substantially alter ambient bank stability and erosion. Three high dams (completed between 1953 and 1963) were built along the Piedmont portion of the Roanoke River, North Carolina; just downstream the lower part of the river flows across largely unconsolidated Coastal Plain deposits. To document bank erosion rates along the lower Roanoke River, >700 bank-erosion pins were installed along 66 bank transects. Additionally, discrete measurements of channel bathymetry, turbidity, and presence or absence of mass wasting were documented along the entire study reach (153 km). A bank-erosionfloodplain-deposition sediment budget was estimated for the lower river. Bank toe erosion related to consistently high low-flow stages may play a large role in increased mid- and upper-bank erosion. Present bank-erosion rates are relatively high and are greatest along the middle reaches (mean 63 mm/yr) and on lower parts of the bank on all reaches. Erosion rates were likely higher along upstream reaches than present erosion rates, such that erosion-rate maxima have since migrated downstream. Mass wasting and turbidity also peak along the middle reaches; floodplain sedimentation systematically increases downstream in the study reach. The lower Roanoke River is net depositional (on floodplain) with a surplus of ~2,800,000 m 3 /yr. Results suggest that unmeasured erosion, particularly mass wasting, may partly explain this surplus and should be part of sediment budgets downstream of dams.