Southern Atlantic Coastal Plain Research Articles

U-Pb and fission-track data from zircon and apatite resolve latest- and post-Alleghanian thermal histories along the Fall Line of the Atlantic margin of the southeastern United States

Abstract Although the Atlantic continental margin of the eastern United States is an archetypal passive margin, episodes of rejuvenation following continental breakup are increasingly well documented. To better constrain this history of rejuvenation along the southern portion of this continental margin, we present zircon U-Pb (ZUPb) age, zircon fission-track (ZFT) age, apatite U-Pb (AUPb) age, and apatite fission-track (AFT) age and length data from six bedrock samples. The samples were collected along the boundary between the exposed Appalachian hinterland (Piedmont province) and the updip limit of passive margin strata (Coastal Plain province). The samples were collected from central Virginia southward to the South Carolina–Georgia border. ZUPb age distributions are generally consistent with geologic mapping in each of the sample areas. The AUPb data are highly discordant owing to high common-Pb abundances, but for two plutons at the northern and southern ends of the sample area, they define a discordia regression line that indicates substantial Permo-Triassic exhumation-driven cooling. ZFT age distributions are highly dispersed but define central values ranging from Permian to Jurassic. AFT data mostly appear to define a singular underlying cooling age, generally approximately Jurassic or Early Cretaceous. Apatite fission tracks are moderately long (mean lengths in the range of ~13.5 µm), however track lengths for one sample in central North Carolina are shorter (~12.5 µm). To interpret the post-breakup thermal history, we present inverse models of time-temperature history for the five plutonic samples. The models show a history of (1) rapid cooling (>10 °C/m.y.) from deep-crustal to near-surface temperatures by the Triassic, (2) hundreds of degrees of Triassic reheating, (3) Jurassic–Early Cretaceous cooling (at rates of 1–10 °C/m.y.), and (4) slow Late Cretaceous–Cenozoic cooling (~1 °C/m.y.). An additional suite of forward models is presented to further evaluate the magnitude of maximum Triassic reheating at one sample site that is particularly well constrained by thermal maturity data. The model results and geologic reasoning suggest that the inverse models may overestimate Triassic paleotemperatures but that other aspects of the inverse modeling are robust. Overall, this thermal history can be reconciled with several aspects of the lithostratigraphy of distal parts of the continental margin, including the lack of Jurassic–earliest Cretaceous strata beneath the southern Atlantic coastal plain and Cretaceous–Cenozoic grain-size trends.

P‐Wave Reflectivity of the Crust and Upper Mantle Beneath the Southern Appalachians and Atlantic Coastal Plain Using Global Phases

AbstractReflection profiles generated using PKPdf as a virtual source show laterally continuous reflections from structures at depths less than 1 km to roughly 200 km beneath the southern Appalachian orogen and Atlantic coastal plain. Arrivals interpreted as reflections from the Moho increase in time from ~10 s beneath the coastal plain to 17.4 s (~57 km) beneath the Blue Ridge Mountains, providing additional evidence that the southern Appalachians are in rough isostatic equilibrium. Reflections at 32–36 s (120–135 km) are consistent with the depth to the base of the lithosphere found in recent inversions of Ps arrivals and surface waves. Alternatively, these and later reflections at times up to 58 s (~224 km) may be due to layering associated with drag‐induced flow in the asthenosphere, suggesting largely horizontal rather than vertical flow for depths less than 225 km beneath the Georgia coastal plain.

Field and Laboratory Dissipation of the Herbicide Fomesafen in the Southern Atlantic Coastal Plain (USA).

To control weeds with evolved resistance to glyphosate, Southeastern (USA) cotton farmers have increased fomesafen (5-(2-chloro-α,α,α-trifluoro-p-tolyloxy)-N-mesyl-2-nitrobenzamide) use. To refine fomesafen risk assessments, data are needed that describe its dissipation following application to farm fields. In our study, relatively low runoff rates and transport by lateral subsurface flow, <1.0 and 0.15% of applied respectively, were observed. The low runoff rate was linked to postapplication irrigation incorporation and implementation of a common conservation tillage practice. Moderate soil persistence (t1/2 = 100 days) was indicated in laboratory incubations with surface soil, however, analysis of soil cores from treated plots showed that ≈3% of fomesafen applied persisted in subsoil >3 years after application. Findings suggest low potential for fomesafen movement from treated fields, however, the fate of fomesafen that accumulated in subsoil and the identity of degradates are uncertain. Soil and water samples were screened for degradates, but, none were detected.

Dissolved Nitrogen, Chloride, and Potassium Loss from Fields in Conventional and Conservation Tillage

Losses of soluble nutrients from cropland and their transport to surface and groundwater are a continuing water quality concern. In this study, we evaluated tillage impacts on dissolved losses of ammonium (NH4-N), nitrate nitrogen (NO3-N), chloride (Cl), and potassium (K) during rotational cotton and peanut production. Tillage treatments were strip tillage (ST), in which crops were planted into 15 cm strips tilled into cover crop residue mulch, and conventional tillage (CT), in which all crop residues were turned into the soil prior to planting. Winter cover crops were used in both tillage systems. Tillage and irrigation treatments were uniformly applied within two 0.6 ha fields located on a moderately sloping hillslope in the southern Atlantic Coastal Plain region of south-central Georgia. Tile drains were installed at the base of the slope of each field to capture and measure lateral subsurface flow. Each field was subdivided into three 0.2 ha plots, with the three plots making up a single tillage block. H-flumes were used for flow measurement and sample collection. During the five-year study, annual precipitation ranged from 910 to 1488 mm, with an annual average of 1201 mm. Annual surface runoff averaged 17% of annual rainfall from the CT field and 11% from the ST field. Because of relatively low variability in concentrations, surface runoff loads closely tracked surface runoff volumes. Annual surface runoff loadings of NH4-N, NO3-N, and Cl from the ST treatment were found to be significantly less than those from the CT treatment. The total five-year load of N (NH4-N and NO3-N) in surface runoff from CT was 8.3 kg ha-1, while it was 5.6 kg ha-1 from ST, equivalent to 1.5% of the total N applied to CT and 1.0% of that applied to ST. Annual subsurface flow averaged 12% of annual precipitation for CT and 21% for ST. Annual average subsurface flow loadings of NH4-N, NO3-N, and K from ST were significantly greater than from CT. The total five-year load of N (NH4-N and NO3-N) in subsurface flow was 45 kg ha-1 from CT and 99 kg ha-1 from ST, equivalent to 8.3% and 18.4% of the total N applied to CT and ST, respectively. Data showed that subsurface flow was the primary hydrologic pathway for dissolved N and Cl loss in both tillage systems. Overall, ST was found to be an effective method for reducing surface runoff and associated soluble losses, but increased infiltration with this practice significantly increased subsurface losses. This introduces a challenge to nitrogen management in reduced tillage systems such as ST in the region.

Sediment Loss and Runoff from Cropland in a Southeast Atlantic Coastal Plain Landscape

<abstract> <bold><sc>Abstract.</sc></bold> Widespread implementation of conservation tillage systems during cotton (Gossypium hirsutum L.) and peanut (Arachis hypogea L.) production in the Atlantic Coastal Plain region of the U.S. has substantially reduced erosion and sediment loss. However, the benefits of conservation tillage in these cropping systems are being threatened by weather shifts that include increased frequency of high-intensity rainfall, policies that encourage the removal of crop residues as cellulosic feedstocks for energy production, and increased herbicide resistance in weeds. Long-term integrated studies are needed to quantify potential impacts. We evaluated runoff and sediment loss from six 0.2 ha fields located on a gently sloping hillslope in a Southern Atlantic Coastal Plain landscape over ten years (2000-2009) during rotational cotton-peanut production, with a rye (Secale cereale) winter cover crop. Half of the fields were in conventional tillage (CT; inversion tillage with cover crop residue incorporation prior to planting), and half were in strip tillage (ST), which is a commonly used conservation tillage practice in the region. Fields were laid out as contrasting tillage pairs at upper, middle, and lower landscape positions and irrigated as needed. Runoff and sediment load from CT fields was significantly greater than from ST fields at each landscape position. Over the 10-year study period, mean annual total sediment load was 1823 kg ha^-1 year^-1 from CT fields and 237 kg ha^-1 year^-1 from ST fields (an 87% difference), and runoff was reduced by 41%. A soil tolerance value (T) of 2,200 kg ha^-1 year^-1 was exceeded in three out of ten years in CT fields and never exceeded in ST fields. On a monthly basis, extreme events (>90th percentile; 10%) accounted for 61% to 72% of the 10-year total sediment load for the CT system (341 to 2,828 kg ha^-1 month^-1) and 73% to 84% for the ST system (49 to 593 kg ha^-1 month^-1). The rainfall and irrigation total was above the normal monthly rainfall in 83% of these extreme monthly periods (mean 179 mm, range 81 to 316 mm). Sediment load was greatest in summer and spring, and during cotton production. The study results improve estimates of the increase in rainfall event size tolerated by CT vs. ST cropping systems, demonstrate the benefits of conservation tillage management during cotton and peanut production, and are expected to guide management decisions that focus on reducing sediment loss in this landscape. Specifically, the results point to the use of cover crops and strip tillage as essential best management practices for this purpose.

Comparative assessment of herbicide and fungicide runoff risk: A case study for peanut production in the Southern Atlantic Coastal Plain (USA)

Peanut (Arachis hypogaea) is produced intensively in the southern Atlantic Coastal Plain of the eastern USA. To effectively protect the region's water quality data are needed which quantify runoff of pesticides used to protect these crops. Fungicides are used intensively yet there is little published data which describe their potential for loss in surface runoff. This study compared runoff of a fungicide, tebuconazole (α-[2-(4-chlorophenyl)ethyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), and an herbicide, metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) from 0.2ha fields in strip (ST), a commonly used conservation-tillage practice, and conventional tillage (CT) near Tifton, GA (USA). Following their first application, metolachlor and tebuconazole were detected at high frequency in runoff. Concentrations and their annual losses increased with application frequency and runoff event timing and frequency with respect to applications, and when fields were positioned at the top of the slope and CT was practiced. Runoff one day after treatment (DAT) contributed to high tebuconazole runoff loss, up to 9.8% of the amount applied on an annual basis. In all cases, metolachlor loss was more than 10 times less even though total application was 45% higher. This was linked to the fact that the one metolachlor application to each crop was in May, one of the region's driest months. In sum, studies showed that fungicide runoff rates may be relatively high and emphasize the need to focus on these products in future studies on peanut and other crops. The study also showed that peanut farmers should be encouraged to use conservation tillage practices like ST which can substantially reduce pesticide runoff.

Extensive clonal growth and biased sex ratios of an endangered dioecious shrub, Lindera melissifolia (Walt) Blume (Lauraceae)1

Plant life history traits like clonal growth and dioecy can complicate endangered species conservation because of the potential for remnant populations to contain few genetically different individuals or a single sex. In this study, we used 11 microsatellite (SSR) markers to characterize fine-scale genetic structure of the endangered dioecious perennial Lindera melissifolia (pondberry) growing in seasonally isolated wetlands across the southern Atlantic Coastal Plain. We found fine-scale genetic structures consistent with extensive clonal growth in all sites. Of the 508 stems sampled across 11 sites, we found 67 genetic individuals (genets), of which 94% were site specific and 39% were represented by a single stem. Individual sites contained from 1 to 16 genets. Spatial genetic analyses showed limited intermingling among different genets within sites, which is consistent with a phalanx clonal growth form. Nine of the eleven sites had biased sex ratios, with six male and three female biased sites. Given our observations of extensive clonal growth, few genetic individuals, and biased sex ratios, we conclude that simple stem counts of this clonal perennial dioecious shrub will grossly overestimate the number of genetic individuals in these remnant southern Atlantic Coastal Plain sites. In order to promote self-sustaining sexually reproducing pondberry populations, as outlined in the pondberry recovery plan, natural areas managers may want to consider introducing unrelated and underrepresented gender plants into sites with few genets or biased sex ratios.

APEX Calibration and Validation of Water and Herbicide Transport under U.S. Southern Atlantic Coastal Plain Conditions

Simulation models are widely used to assess water contamination risk associated with pesticide use and for evaluating effectiveness of agricultural conservation practices. Currently, the APEX (Agricultural Policy/Environmental eXtender) model is being used for this purpose in the USDA Conservation Effects Assessment Project (CEAP) Cropland National Assessment. In support of the CEAP modeling effort, APEX was calibrated and validated using a nine-year record (1999-2007) of crop yield, surface runoff, and tile outflow and an eight-year record (1999-2006) of soluble pendimethalin and fluometuron herbicide losses from fields in a cotton-peanut rotation located in the Atlantic Coastal Plain region of south-central Georgia. Conventional tillage and strip tillage were directly compared. Monthly surface runoff was calibrated by adjusting three variables: curve number index coefficient (CNIC), a driver of the USDA Natural Resources Conservation Service (NRCS) runoff curve number; runoff curve number for the average soil moisture condition 2 (CN2); and irrigation runoff ratio (IRR). Statistical performance criteria for monthly and annual results were r2 > 0.5, NSE > 0.45, and PBIAS < 20%, based on prior modeling studies. Monthly runoff statistics showed r2 values of 0.62 to 0.82 and met satisfactory criteria between observed and simulated surface runoff for both tillage types, with Nash-Sutcliffe efficiency (NSE) values of 0.62 to 0.80 and PBIAS values within 19% during the calibration and validation periods. Monthly subsurface lateral flow performance statistics for the strip-tilled plots were satisfactory during the calibration period but weak for the conventional tillage plots. Monthly performance statistics for fluometuron runoff for the conventional tillage plots were below satisfactory criteria. Other monthly statistics for fluometuron and pendimethalin losses were weak. Measured and predicted crop yield and annual runoff for both tillage systems were well aligned and met satisfactory statistical criteria. APEX performance was satisfactory for annual fluometuron soluble runoff for the conventionally tilled plots but not satisfactory for the strip-tilled plot with less runoff. The models performance was unsatisfactory for annual subsurface lateral flow and fluometuron transport in subsurface lateral flow for both tillage systems. The percent bias statistical parameter (PBIAS) was within 20% for all annual mean correlations, indicating that APEX effectively replicated annual means for crop yield, runoff, subsurface lateral flow, and pesticide losses. Measured and simulated results of conservation tillage effects were in close agreement for decreased water and pesticide runoff as well as increased subsurface lateral flow and associated fluometuron losses. Although fluometuron losses in subsurface lateral flow approximately doubled with conservation tillage, loading was still small compared to fluometuron in runoff from the conventionally tilled plots. Results demonstrate APEXs strength in simulating runoff in this landscape, but less satisfactory results were obtained for pendimethalin runoff, subsurface lateral flow, and fluometuron losses in subsurface lateral flow.

Evaluating fuel complexes for fire hazard mitigation planning in the southeastern United States

Fire hazard mitigation planning requires an accurate accounting of fuel complexes to predict potential fire behavior and effects of treatment alternatives. In the southeastern United States, rapid vegetation growth coupled with complex land use history and forest management options requires a dynamic approach to fuel characterization. In this study we assessed potential surface fire behavior with the Fuel Characteristic Classification System (FCCS), a tool which uses inventoried fuelbed inputs to predict fire behavior.Using inventory data from 629 plots established in the upper Atlantic Coastal Plain, South Carolina, we constructed FCCS fuelbeds representing median fuel characteristics by major forest type and age class. With a dry fuel moisture scenario and 6.4kmh−1 midflame wind speed, the FCCS predicted moderate to high potential fire hazard for the majority of the fuelbeds under study. To explore fire hazard under potential future fuel conditions, we developed fuelbeds representing the range of quantitative inventory data for fuelbed components that drive surface fire behavior algorithms and adjusted shrub species composition to represent 30% and 60% relative cover of highly flammable shrub species.Results indicate that the primary drivers of surface fire behavior vary by forest type, age and surface fire behavior rating. Litter tends to be a primary or secondary driver in most forest types. In comparison to other surface fire contributors, reducing shrub loading results in reduced flame lengths most consistently across forest types. FCCS fuelbeds and the results from this project can be used for fire hazard mitigation planning throughout the southern Atlantic Coastal Plain where similar forest types occur. The approach of building simulated fuelbeds across the range of available surface fuel data produces sets of incrementally different fuel characteristics that can be applied to any dynamic forest types in which surface fuel conditions change rapidly.

Patterns of differentiation among endangered pondberry populations

Pondberry, Lindera melissifolia, is an endangered and partially clonally reproducing shrub species found in isolated populations that inhabit seasonally wet depressions in forested areas of the lower Mississippi River alluvial valley and southeastern regions of the United States. With eleven microsatellite loci, we quantified population genetic differentiation and diversity among 450 genets in 10 locations distributed across pondberry’s range. We used estimates of F st and Jost’s D est to measure genetic differences between populations and between geographic regions. The largest pairwise regional difference was found between eastern and western regional population groups (F st = 0.23, D est = 0.67), with the northern-most population groups in each region exhibiting larger divergence from each other than the southern-most population groups. Genetic diversity was lowest in the Sand Pond Conservation Area (A e = 1.9, H e = 0.36), which was the northern-most pondberry population, and highest in the Francis Marion National Forest (A e = 4.1, H e = 0.69), although we identified only 17 genets in that admixed population. Following adjustments for estimated null allele frequencies, we identified heterozygote excess in four eastern populations and found no evidence for inbreeding in any population. The observed patterns of differentiation indicate a phylogeography that exhibits an Appalachian Mountain discontinuity coupled with northward migrations along the Southern Atlantic Coastal Plain and into the Mississippi Alluvial Plain. The genetic consequences of this proposed phylogeographical structure may affect selection of germplasm sources for population reestablishment programs across pondberry’s range.

Modeling the longitudinal variation in wood specific gravity of planted loblolly pine (Pinus taeda) in the United States

Loblolly pine (Pinus taeda L.) is a major plantation species grown in the southern United States, producing wood having a multitude of uses including pulp and lumber production. Specific gravity (SG) is an important property used to measure the quality of wood produced, and it varies regionally and within the tree with height and radius. SG at different height levels was measured from 407 trees representing 135 plantations across the natural range of loblolly pine. A three-segment quadratic model and a semiparametric model were proposed to explain the vertical and regional variations in SG. Both models were in agreement that a stem can be divided into three segments based on the vertical variation in SG. Based on the fitted models, the mean trend in SG of trees from the southern Atlantic Coastal Plain and Gulf Coastal Plain was observed to be higher than in other physiographical regions (Upper Coastal Plain, Hilly Coastal Plain, northern Atlantic Coastal Plain, and Piedmont). Maps showing the regional variation in disk SG at a specified height were also developed. Maps indicated that the stands in the southern Atlantic Coastal Plain and Gulf Coastal Plain have the highest SG at a given height level.

Taxonomic reassessment of Zale lunifera (Hübner) (Erebidae, Erebinae)

In light of the recent discovery of an unrecognized species within nominal Zale lunifera (Hubner), the taxonomy of Z. lunifera is reassessed. Zale intenta (Walker), stat. rev. is the name that applies to the widespread species previously called Z. lunifera. Zale lunifera sensu stricto is the species previously thought to be undescribed; it occurs from the southern Atlantic coastal plain northward to the pine barrens of north-eastern United States. A differential diagnosis and adult illustrations of the two species are given.

Scale-bearing chrysophytes from the Southern Atlantic Coastal Plain in Louisiana, U.S.A. II. Extended studies on identification, ecology, and distribution

Scale-bearing chrysophytes from the Southern Atlantic Coastal Plain in Louisiana, U.S.A. II. Extended studies on identification, ecology, and distribution

Fluometuron and Pendimethalin Runoff from Strip and Conventionally Tilled Cotton in the Southern Atlantic Coastal Plain

In the Atlantic Coastal Plain region of southern Georgia (USA), cotton (Gossypium hirsutum L.) acreage increased threefold in the past decade. To more effectively protect water quality in the region, best management practices are needed that reduce pesticide runoff from fields in cotton production. This study compared runoff of two herbicides, fluometuron [N,N-dimethyl-N'-[3-(trifluoromethyl)-phenyl]-urea] and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine], from plots in strip-tillage (ST) and conventional-tillage (CT) management near Tifton, GA. Rainfall simulations were conducted one day after preemergence herbicide applications to 0.0006-ha plots and runoff from 0.15-ha plots due to natural rainfall following preemergence pendimethalin and fluometuron and postemergence fluometuron use was monitored. Pendimethalin runoff was greater under CT than ST due to strong pendimethalin soil sorption and higher erosion and runoff under CT. The highest losses, 1.3% of applied in CT and 0.22% of applied in ST, were observed during rainfall simulations conducted 1 DAT. Fluometuron runoff from natural rainfall was substantially lower from ST than from CT plots but the trend was reversed in rainfall simulations. In all studies, fluometuron runoff was also relatively low (<1% of applied), and on plots under natural rainfall, desmethylfluometuron (DMF) represented about 50% of total fluometuron runoff. Fluometuron's relatively low runoff rate appeared linked to its rapid leaching, and high DMF detection rates in runoff support DMF inclusion in fluometuron risk assessments. Results showed that ST has the potential to reduce runoff of both herbicides, but fluometuron leaching may be a ground water quality concern.

Stratigraphic and climatic implications of clay mineral changes around the Paleocene/Eocene boundary of the northeastern US margin

Abstract Kaolinite usually is present in relatively small amounts in most upper Paleocene and lower Eocene neritic deposits of the northern US Atlantic Coastal Plain. However, there is a short period (less than 200,000 k.y.) in the latest Paleocene (upper part of calcareous nannoplankton Zone NP 9) when kaolinite-dominated clay mineral suites replaced the usual illite/smectite-dominated suites. During this time of global biotic and lithologic changes, kaolinite increased from less than 5% of the clay mineral suite to peak proportions of 50–60% of the suite and then returned to less than 5% in uppermost Paleocene/lowermost Eocene strata. This kaolinite pulse is present at numerous localities from southern Virginia to New Jersey. These sites represent both inner and middle neritic depositional environments and reflect input from several river drainage systems. Thus, it is inferred that kaolinite-rich source areas were widespread in the northeastern US during the latest Paleocene. Erosion of these source areas contributed the kaolinite that was transported and widely dispersed into shelf environments of the Salisbury embayment. The kaolinite increase, which occurred during a time of relatively high sea level, probably is the result of intensified weathering due to increased temperature and precipitation. The southern extent of the kaolinite pulse is uncertain in that uppermost Paleocene beds have not been identified in the southern Atlantic Coastal Plain. The late Paleocene kaolinite pulse that consists of an increase to peak kaolinite levels followed by a decrease can be used for detailed correlation between more upbasin and more downbasin sections in the Salisbury embayment. Correlations show that more upbasin Paleocene/Eocene boundary sections are erosionally truncated. They have varying portions of the kaolinite increase and, if present at all, discontinuous portions of the subsequent kaolinite decrease. As these truncated sections are disconformably overlain by lower Eocene strata, rapid erosional removal of large parts of the most kaolinite-rich P/E boundary clay deposits occurred by early Eocene time. Erosion of the kaolinite-rich P/E boundary beds was enhanced during times of sea-level fall when kaolinite-rich sediments were redeposited to produce kaolinite spikes in basal beds of lower and middle Eocene sequences that have little or no kaolinite elsewhere in the sequence. In contrast, more downbasin sites document only the upper, decreasing part of the kaolinite pulse. The absence of strata documenting the earlier kaolinite increase is attributed to slow sedimentation (condensed interval) as a result of a significant sea level rise that ponded most sediments in shallower waters, combined with the probable subsequent erosional removal of these thin downbasin deposits by oceanic currents.

The ecology, status, and conservation of two non-alluvial wetland communities in the South Atlantic and Eastern Gulf coastal plain, USA

The existence and integrity of the majority of southern Atlantic and eastern Gulf coastal plain non-alluvial wetlands (and the plant and animal species dependent on these communities) are critically threatened. Federal efforts and public interest have concentrated on the protection of coastal wetlands and riverine bottomlands, but many other coastal plain wetland communities are declining rapidly. Among these threatened natural communities are non-alluvial systems such as pond cypress Taxodium ascendens savannas, karst ponds, coastal plain small depression ponds, longleaf pine Pinus palustris savannas, and pocosins. We estimate that more than a third of the rare plant species in the Southeast occur in these wetland communities. The threats to these isolated wetland communities are numerous, from local site specific threats including drainage and development to threats to the regional hydrology. In this paper we present an overview of the non-alluvial wetlands in the southern Atlantic and eastern Gulf coastal plain and focus on two of the most threatened non-alluvial wetland communities in the region, pond cypress savannas and karst ponds.

Synurophyceae from the Southern Atlantic Coastal Plain of North America: A preliminary survey in Louisiana, USA

Forty‐three taxa of Synurophyceae were identified by means of transmission electron microscopy of samples from ten different localities in southeastern Louisiana, USA, on the southern portion of the Atlantic Coastal Plain Province of North America. Samples were collected during a one month period when water temperatures ranged from 15.5–24.5“C. Sample pH values ranged from 4.4–7.2. Notable scale morphology variation was described for some taxa. The flora included three warm water taxa but was dominated by temperate and cosmopolitan taxa. Mallomonas prora and Synura australiensis are reported for the first time from North America. Comparisons with related studies from New World subtropical regions in Florida, USA, and Argentina were made, and significant North American range expansions were noted. The large number of aquatic habitats, 7–8 consecutive months at temperatures (6–20°C) best suited for development of synurophycean populations, and proximity to major bird migrations routes are postulated as explanations for the large number of reported species.

Urban/rural contrasts in vertebrate fauna from the Southern Atlantic coastal plain

A review of archaeological faunal data from urban and rural settings on the southern Atlantic coastal plain indicates that contrasts in these collections reflect the urban or non-urban setting of each site within this natural setting. These contrasts may be seen in the data despite probable differences in socioeconomic status of the sites’ occupants. Apparently, urban households consumed more meat from domestic animals than did rural households, regardless of social status. Rural faunal deposits are more diverse than urban ones and contained large amounts of fish instead of domestic animals. Data for this analysis are taken from 16 archaeological sites excavated at Charleston, South Carolina; Savannah, Georgia; St. Simons Island, Georgia; and elsewhere on the Georgia coast. The combined samples contained 1576 individuals from sites occupied between the mid-18th century and the mid-19th century.

Appalachian thrusting, lithospheric flexure, and the Paleozoic stratigraphy of the Eastern Interior of North America

The Appalachian Basin is interpreted to be a multistage foreland basin developed by lithospheric downwarp under the loads of successive Taconic, Acadian, and Alleghanian overthrusts in the adjacent Appalachian Mountains. By quantifying this model we show how the stratigraphic record of the foreland basin can be used to constrain the timing, areal distribution, and thickness of the orogenic overthrusts. The cumulative present-day thickness of these allochthonous units is suggested to range from 4 to 18 km with the greatest thickness in the vicinity of Pennsylvania and Virginia. These model load thicknesses compare favourably with those implied by the COCORP seismic profile across the southern Appalachians and Atlantic Coastal Plain. We further suggest that, for reasons of isostatic balance, these thick overthrusts are likely to rest on the old Cambro-Ordovician continental margin, a conclusion also in keeping with, but independent of, COCORP results. The distribution of model loads is qualitatively correlative with observed patterns of regional Bouguer gravity anomalies but we have not as yet attempted quantitative gravity calculations.Flexural interactions between the Appalachian Basin and the contemporaneous intracratonic Michigan and Illinois basins produced the interbasinal Kankakee, Findlay–Algonquin, and Cincinnati arches as well as the Jessamine and Nashville domes. These arches and domes existed in fluctuating submergent and emergent conditions, alternately yoking together and decoupling the foreland basin and one or both of the intracratonic basins. The location and magnitude of Appalachian overthrusting and the lithosphere's rheological behaviour are the primary controls on arch development. The most satisfactory stratigraphic results are achieved using a lithospheric model with a temperature-dependent Maxwell viscoelastic rheology. In such a lithosphere the lower regions relax load-induced stress on time scales of 1–200 Ma but the upper regions are too viscous to flow on time scales less than the age of the Earth.We propose no explanation for the initiation of subsidence in the intracratonic Michigan and Illinois basins. Nevertheless, we show that the sediment record of these basins is likely to have been substantially modified by the influence of Appalachian overthrusts. This influence should be removed before attempting to interpret the sedimentary record of the intracratonic basins in terms of a basin-initiating mechanism.Viscoelastic relaxation is shown to provide a natural explanation for the unconformities that bound Sloss' sedimentary sequences in those parts of the basins well removed from the overthrusts. The onset and termination of erosion that created the unconformities correlate with the termination and initiation, respectively, of overthrust episodes. Sloss' sequences are seen as marking intervals of major orogenic overthrusting in the Appalachians. Insofar as the periods of thrusting are a consequence of worldwide plate tectonic reorganization, the stratigraphic sequences may have worldwide synchroneity but they are shown to have a more immediate local tectonic origin.

Amino acid age estimates, quaternary Atlantic Coastal Plain: Comparison with U-series dates, biostratigraphy, and paleomagnetic control

Amino acid enantiomeric ( D L ) ratios in the mollusk Mercenaria are compared with recently published biostratigraphic and/or U-series solitary coral data from 22 Quaternary localities on the central and southern Atlantic Coastal Plain. In all cases, local relative aminostratigraphic sequences are consistent with relative ages inferred from U-series or biostratigraphic data, although occasionally more depositional events are recognized by aminostratigraphic than biostratigraphic methods. However, if the U-series data are used as age calibrations for the D L values, latitudinal trends of “isochronous” D L values are highly variable and conflict with trends expected from the present temperature gradient, which is smooth and nearly linear between 45° and 25° N. Age estimation can be performed independently of the U-series data using a kinetic model that relies on the assumption that Pleistocene temperature gradients have also been smooth functions of latitude, although significantly steeper than the present temperature gradient. Within the uncertainties of this assumption, kinetic model age estimates for localities in the coastal plain fall into the following groups: 70,000–130,000 yr, 200–250,000 yr, 300,000–400,000 yr, 500,000–600,000 yr, 700,000–800,000 yr, and > 1,000,000 yr. Major conflicts between these model age estimates are observed for localities near Charleston, South Carolina and in central Virginia. These conflicts could indicate that the basic temperature assumptions of aminostratigraphy are incorrect, and that apparent local aminostratigraphic sequences (clusters of different D L values) could be due to factors other than age difference. Alternatively, some of the U-series dates may be only minimum ages for these localities.