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.     

A post-Calumet shoreline along southern Lake Michigan

The southern shore of Lake Michigan is the type area for many of ancestral Lake Michigan’s late Pleistocene lake phases, but coastal deposits and features of the Algonquin phase of northern Lake Michigan, Lake Huron, and Lake Superior are not recognized in the area. Isostatic rebound models suggest that Algonquin phase deposits should be 100 m or more below modern lake level. A relict shoreline, however, exists along the lakeward margin of the Calumet Beach that was erosional west of Deep River and depositional east of the river. For this post-Calumet shoreline, the elevation of basal foreshore deposits east of Deep River and the base of the scarp west of Deep River indicate a slightly westward dipping water plane that is centered at ∼184 m above mean sea level. Basal foreshore elevations also indicate that lake level fell ∼2 m during the development of the shoreline. The pooled mean of radiocarbon dates from the surface of the peat below post-Calumet shoreline foreshore deposits indicate that the lake transgressed over the peat at 10,560 ± 70 years B.P. Pollen assemblages from the peat are consistent with this age. The elevation and age of the post-Calumet shoreline are similar to the Main Algonquin phase of Lake Huron. Recent isostatic rebound models do not adequately address a high-elevation Algonquin-age shoreline along the southern shore of Lake Michigan, but the Goldthwait (1908) hinge-line model does.     

Paleoecology and high-resolution paleohydrology of a kettle peatland in upper Michigan

We investigated the developmental and hydrological history of a Sphagnum-dominated, kettle peatland in Upper Michigan using testate amoebae, plant macrofossils, and pollen. Our primary objective was to determine if the paleohydrological record of the peatland represents a record of past climate variability at subcentennial to millennial time scales. To assess the role of millennial-scale climate variability on peatland paleohydrology, we compared the timing of peatland and upland vegetation changes. To investigate the role of higher-frequency climate variability on peatland paleohydrology, we used testate amoebae to reconstruct a high-resolution, hydrologic history of the peatland for the past 5100 years, and compared this record to other regional records of paleoclimate and vegetation. Comparisons revealed coherent patterns of hydrological, vegetational, and climatic changes, suggesting that peatland paleohydrology responded to climate variability at millennial to sub-centennial time scales. Although ombrotrophic peatlands have been the focus of most high-resolution peatland paleoclimate research, paleohydrological records from Sphagnum-dominated, closed-basin peatlands record high-frequency and low-magnitude climatic changes and thus represent a significant source of unexplored paleoclimate data.     

GIS Methodology for Characterizing Historical Conditions of the Willamette River Flood Plain, Oregon

Recent environmental developments have stimulated an interest in conservation and restoration of the historical Willamette River flood plain, both to protect against flooding and to provide wildlife habitat. In order to best utilize scarce resources, we characterized historical and modern river channel and flood‐plain conditions to evaluate changes and help prioritize restoration sites. Using cartographic and photographic data sources, we developed a Geographic Information System (GIS) to map active channels, side channels, islands and tributaries for four separate dates, as well as riparian and flood‐plain vegetation characteristics for pre‐European settlement and modern time periods. Coverages based on flood records and other boundaries were used to partition the flood plain into spatial subsets for analysis. The GIS allowed comparisons between historical and present conditions for a variety of environmental factors. Much of the pre‐settlement channel complexity has been removed. Total channel length in 1995 was 26% less than in 1850, with almost 58% of the river's side channels disconnected from the system. In addition, we found a 72% loss of flood‐plain forest from 1850 to 1995, since it was converted to agricultural and urban land uses. Selected river and flood‐plain variables were made available for a spatial model to prioritize potential locations for flood‐plain restoration.     

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.