Aminostratigraphic results from Cape Lookout, N.C., and their relation to the preserved Quaternary marine record of SE North Carolina

Aminostratigraphic data were obtained for Mulinia lateralis samples from closely spaced drillholes on the Cape Lookout, North Carolina barrier islands. Two major aminozones are recognized in the subsurface section based upon D-alloisoleucine/L-isoleucine (A/I) values. These major aminozones can each be subdivided into two additional aminozones based upon direct comparisons with Mulinia A/I data from other North Carolina localities. Correlation of the Cape Lookout Mulinia aminostratigraphy with U-series calibrated A/I data in N.C. indicates that the sampled units represent deposition during the middle to late Pleistocene. The four Cape Lookout aminozones may be assigned to late and early stage 5 (or possibly stages 5 and 7), a portion of the interval during stages 17–19, and at least one interglacial in stages 25–31 of the oxygen isotope record based on correlation to calibrated sites and kinetic model extrapolation.

The aminostratigraphic data obtained from the Cape Lookout barrier islands and nearby areas indicate that there are significant differences in the extent of preservation of the Pleistocene sedimentary record to the southwest of Cape Lookout compared with that to the north-northeast. All four of the recognized Cape Lookout aminozones are present in the subsurface section to the north-northeast of Cape Lookout. In contrast, the two late Pleistocene aminozones are almost completely absent in the subsurface of the barrier islands, and in Onslow Bay, to the southwest of Cape Lookout. These aminostratigraphic interpretations are consistent with the incomplete stratigraphic record recognized by previous investigators for the Cape Lookout-Onslow Bay area. The calibrated kinetic model age estimates for the Cape Lookout aminostratigraphic data now permit quantification of these stratigraphic gaps. The detailed aminostratigraphic results from Cape Lookout also have significant consequences for regional aminostratigraphic correlations on the Atlantic Coastal Plain, and provide valuable information with which to test contrasting models proposed for regional correlation within the context of the preserved stratigraphic record.     

IAHS/AGU symposium on groundwater contamination

Papers presented at a two-day jointly sponsored IAHS/AGU symposium on groundwater contamination are briefly summarized. This international symposium was held 11–12 May, 1989, in Baltimore, Maryland. Presentations encompassed recent research developments in three general areas: abiotic and biotic processes governing contaminant transport; aquifer rehabilitation; and the influence of agricultural practices and nonpoint sources on aquifer quality. Contributions offered an interesting mixture of theoretical, mathematical, laboratory, and field studies. In the first session, transport processes explored ranged from dispersion and fingering to nonequilibrium sorption, metals complexation, and bacteria migration. The use of optimization modeling in the design of remediation strategies was the focus of another session. Here theoretical studies were presented alongside case histories of aquifer rehabilitation. In a final session, a number of models for agricultural management were described. These presentations were complemented by case studies of actual aquifer degradation resulting from land-use and management practices.     

Photosynthesis and respiration ofSpartina andJuncus salt marshes in North Carolina: Some models

In situ ecosystem gas exchange measurements were taken monthly for a 15-month period during low tide forJuncus roemerianus Scheele and short, medium, and tall height forms ofSpartina alterniflora Loisel. in three salt marshes near Southport, North Carolina. Multiple regression analysis was used to obtain empirical relationships betwen gas exchange values and the physical and biotic variables measured. Preliminary models for net ecosystem photosynthesis, ecosystem respiration, and respiration of aboveground standing crop were developed. Validation of models was carried out in the following manner: (1) net primary productivity of aboveground standing crop was calculated from model data and compared with harvest estimates of net primary productivity for the same year; and (2) carbon exchange and energy efficiency values were compared with literature values. In general, theSpartina models, because of their larger data base, were more useful than theJuncus models. Annual primary productivity of aboveground standing crop calculated from gas exchange values was 1.8 to 3.6 times greater forSpartian than values calculated from harvest data by Smalley's method.Juncus values were approximately equal. Since values calculated from carbon data and harvest data are not entirely equivalent, required adjustments to the carbon values are discussed. Both species have two growth periods—one in ths pring and one in the fall—with the spring growth in excess of that in the fall. Net ecosystem productivity was highest in the spring and lowest in the summer. Ecosystem respiration amounted to 71% of gross annual photosynthesis. The aboveground standing crop contributed approximately 35% to this ecosystem respiration and the soil, the remaining 36%. Efficiency for gross photosynthesis per unit of solar radiation ranged from 0.22 to 1.11%. Efficiencies for net primary production of aboveground standing crop ranged from 0 to 0.82% and those of net ecosystem production from 0 to 0.56%.     

Incorporation of trivalent chromium into riverine and estuarine colloidal material

The binding of dissolved trivalent chromium by dissolved and colloidal substrates at the riverestuary interface was studied using a combination of product and reactant mode experiments, at concentrations of materials typical of estuarine conditions. Using spikes of 1–20 μg/l Cr³⁺, about one third of the Cr³⁺ was scavenged by that fraction of riverine colloidal material which flocculated upon mixing of river water and seawater. Reactant mode experiments, using chemiluminescence as a speciation technique, showed that virtually all of the spiked Cr³⁺ was bound by dissolved or colloidal substrates, but that the higher molecular weight fractions were able to kinetically outcompete the lower molecular weight fractions. There was no effect of salinity or the flocculation process on the binding of Cr by riverine substrates at natural concentrations. However, salinity did produce a strong kinetic inhibition of binding if the river water was first diluted. This salinity response is likely a result of a wide variety of Cr binding site energies on the substrates.     

Isotopic evidence for the origin of sulfur in the Herrin (no. 6) coal member of Illinois

The sulfur isotopic composition of the Herrin (No. 6) Coal from several localities in the Illinois Basin was measured. The sediments immediately overlying these coal beds range from marine shales and limestones to non-marine shales. Organic sulfur, disseminated pyrite, and massive pyrite were extracted from hand samples taken in vertical sections.The $\text{δ}{}^{34}\text{S}$ values from low-sulfur coals (< 0.8% organic sulfur) underlying nonmarine shale were +3.4 to +7.3%₀ for organic sulfur, +1.8 to +16.8%₀ for massive pyrite, and +3.9 to +23.8%₀ for disseminated pyrite. In contrast, the $\text{δ}{}^{34}\text{S}\text{values from high-sulfur coals}$ (> 0.8% organic sulfur) underlying marine sediments were more variable: organic sulfur, ?7.7 to +0.5%₀, pyrites, ?17.8 to +28.5%₀. In both types of coal, organic sulfur is typically enriched in ³⁴S relative to pyritic sulfur.In general, δ ³⁴S values increased from the top to the base of the bed. Vertical and lateral variations in δ ³⁴S are small for organic sulfur but are large for pyritic sulfur. The sulfur content is relatively constant throughout the bed, with organic sulfur content greater than disseminated pyrite content. The results indicate that most of the organic sulfur in high-sulfur coals is derived from post-depositional reactions with a ³⁴S-depleted source. This source is probably related to bacterial reduction of dissolved sulfate in Carboniferous seawater during a marine transgression after peat deposition. The data suggest that sulfate reduction occurred in an open system initially, and then continued in a closed system as sea water penetrated the bed.Organic sulfur in the low-sulfur coals appears to reflect the original plant sulfur, although diagenetic changes in content and isotopic composition of this fraction cannot be ruled out. The wide variability of the δ ³⁴S in pyrite fractions suggests a complex origin involving varying extents of microbial H₂S production from sulfate reservoirs of different isotopic compositions. The precipitation of pyrite may have begun soon after deposition and continued throughout the coalification process.     

Certification of four North-American Gypsum Rock Samples Type: Calcium Sulphate Dihydrate, CaSO4.2H2O, GYP-A, GYP-B, GYP-C and GYP-D

Four natural gypsum rock samples were prepared and certified for major elements and some trace elements by the Analytical Group of Domtar Inc., Research Centre in Senneville (Montréal), Québec, Canada with the cooperation of Domtar Gypsum Products Laboratory in Caledonia, Ontario, Canada. The analytical round-robin results received from 29 participating laboratories were statistically evaluated, summarized, and form the basis of this paper. These certified reference materials are primarily intended as calibration standards for the determination of major and minor elements in gypsums and gypsum related minerals and products. As certified gypsum rock samples were not available on the North-American or world markets, these may be particularly important not only to the gypsum and cement industries, but also to geochemists, geologists and analysts of minerals and ores.     

Multiple states in the sea-level induced transition from terrestrial forest to estuary

In this paper we provide a conceptual model to examine changes in ecosystem state during the transition from terrestrial forest to shallow estuarine environments for coastal mainland marshes at the Virginia Coast Reserve (VCR), United States of America. Ecosystem states are characterized by plant community dominants and soil/sediment characteristics. The five states considered are upland or wetland forest, organic high marsh, intertidal mineral low marsh, autotrophic benthic with or without submersed aquatic vascular plants, and heterotrophic benthic (estuarine bottom). Transitions between states are described from the perspective of a fixed forest location undergoing transition from one ecosystem state to another. Rising sea level is acknowledged as the master variable that forces the process of change overall. Each state is hypothesized to have self-maintaining properties and thus is resistant to change from rising sea level; alternatively, transitions between states are facilitated by disturbance or exposure to acute stress. For change to occur, resistance must be overcome by events that are more abrupt than rising sea level and that appear as accentuated pulsings, which result in another self-maintaining and resistnnt state. Such events facilitate plant species replacement and alter sediment conditions. Mechanisms responsible for causing a state to cross a threshold are unique for each transition type and include brackish-water intrusion (osmotic stress and sulfide toxicity), tidal creek encroachment (redistribution of sediments), erosive currents and waves (resuspension of sediments, which increases light extinction), and increasing water depth (leads to greater bottom shading). Field experiments relevant to scales at which pulsings occur are not abundant in coastal marshes.