Paper plant effluent revisited-southern Lake Champlain, Vermont and New York

We used geologic and geochemical techniques to document the change with time of the distribution and concentration of contaminated bottom sediments in southern Lake Champlain near an International Paper Company plant. Our work, initiated in 1972, was expanded on behalf of Vermont citizens in a class-action suit against the International Paper Company. To update our 1972–1973 results, we collected nine cores in 1988 upstream and downstream from the paper plant effluent diffuser. Water content, volatile solids, organic carbon, and three ratios, Al/Si, Cl/Si, and S/Si, in addition to megascopic and microscopic observations, were evaluated to identify and trace the distribution of effluent and to measure the thickness of sediment affected by or containing components of effluent. Analyses were carried out on samples from the cores as well as from effluent collected directly from the plant's waste treatment facility. In 1973, two years after the plant opened, we cored near the diffuser; sediment contaminated with effluent was 4.5 cm thick. In 1988, in the same area, sediment contaminated with effluent was 17 cm thick. In 15 years, water content increased from 72 to 85 percent, volatile solids from 7 to 20 percent, and organic carbon from 2 to 12 percent. Cl/Si and S/Si were high only near the diffuser and were zero elsewhere. In the area of the diffuser, contaminated sediment appears to be accumulating at a rate of about 1 cm/yr. At a control location 22 km upstream (south) from the plant, the top, poorly consoli-dated layer was only 1 cm or less thick both in 1973 and in 1988. The class-action suit was settled in favor of the plaintiffs for $5 million.     

The origin and distribution of subbottom sediments in southern Lake Champlain

Three units, correlatable with recent Lake Champlain, late-glacial marine Champlain Sea, and proglacial Lake Vermont sediments, have been identified from about 200 km of high-resolution seismic reflection profiles and eight piston cores collected in southern Lake Champlain. Lake Vermont deposits are nonfossiliferous and range from thin to absent nearshore and on bedrock highs to more than 126 m thick near Split Rock Point. Champlain Sea sediments contain marine foraminifers and ostracodes and are fairly uniform in thickness (20–30 m). Recent Lake Champlain sediments range in thickness from 0 to 25 m. Average sedimentation rates for Lake Vermont are considerably higher (4–8 cm/yr) than those for the Champlain Sea (0.8–1.2 cm/yr) and Lake Champlain (0.14–0.15 cm/yr). Bedrock, till, and deltaic and alluvial deposits were also identified on the acoustic records but were not sampled. An unconformity separating Champlain Sea deposits from Lake Champlain deposits is associated with numerous benches at water depths of 20–30 m. These benches, the alluvial deposits, and the onset of deltaic deposition are probably associated with a low water level stillstand at the close of the Champlain Sea episode.     

The sedimentary framework of the southern basin of Lake George,New York

Information from 240 km of high-resolution seismic reflection profiles has been analyzed to show the bathymetric and subsurface configuration of southern Lake George in the southeastern corner of the Adirondack Mountains, New York. Three units have been identified and sampled in 13 piston cores as long as 7 m and 4 grab samples; they are glacial drift, glaciolacustrine nonorganic clay, and Holocene lake mud rich in organic material. Three deep bedrock basins controlled glacial, glaciolacustrine, and postglacial deposition within the lake. Glaciolacustrine clay is more than 30 m thick in these basins but is generally absent in water depths less than 20 m. An unconformity separates glaciolacustrine clay from overlying Holocene mud in water depths less than 30 m, but the contact is conformable and transitional in deeper water. The unconformity may have originated from subaqueous or subaerial erosion during a low stage of lake level which probably occurred between 10,000 and 700 yr B.P. Holocene lake mud is thin to absent in the shallower waters separating the three basins, but reaches 15-m thickness near the entrance to The Narrows. A new radiocarbon date of 6950 ± 60 yr B.P. was obtained from a wood fragment which was found in the Holocene lake mud. We found no clear evidence of postglacial tectonic disturbances of the lake sediments although recent releveling profiles suggest that the Adirondack Mountains are undergoing contemporary uplift.     

Late-Wisconsin marine environments of the Champlain Valley (New York,Quebec)

The Champlain Sea occupied the Champlain Valley from about 12,500 to 10,000 yr BP. Following an initial maximum limit of inundation, isostatic crustal rebound caused the sea's gradual regression, which is documented by the parallel alignment of tilted shoreline features at successively low elevations along a north-south profile. Two new radiocarbon shell dates, 11,665 ± 175 (QC 200), elevation 95 m, and 10,300 ± 180 (QC 199), elevation 47 m, date early and late Champlain Sea deposits, respectively. From the elevation (ASL) and invertebrate fauna of littoral deposits, three environmentally distinct phases of the sea were recognized. Early Champlain Sea Transitional phase deposits at high elevations are characterized by a mixed association of fresh and euryhaline marine ostracodes. Frigid-subfrigid climates and fluctuating salinities of this period possibly reflect intermixing of the fresh waters of Lake Vermont with incoming marine waters. Hiatella arctica phase faunas indicate similar climatic conditions but significantly higher salinities (polyhaline). Deposits from the final phase of the sea, the Mya arenaria phase, were found at low elevations just above the present level of Lake Champlain. A predominantly cold-temperate, mesohaline fauna characterizes this period. The influences of Lake Algonquin drainage, warm Gulf Stream water and perhaps the retreating Laurentide Ice Sheet are discussed as possible causes for the observed faunal and environmental changes.     

One-dimensional thermal modelling of Acadian metamorphism in southern Vermont, USA

One‐dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet‐grade pre‐Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda–Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite‐ or kyanite‐grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P–T paths, and temperature–time (T –t) and pressure–time (P–t) curves. Information extracted from P–T –t modelling includes values of maximum temperature and pressure on the P–T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K‐feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet‐grade versus staurolite‐grade or kyanite‐grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated exhumation rates, and differences in ⁴⁰Ar/³⁹Ar closure ages are likely to have been consequences of variations in the duration of isobaric heating (or ‘crustal residence periods’) and tectonic unroofing rates. Modelling results are consistent with a regional structural model that suggests west to east younging of specific Acadian deformational events, and therefore diachroneity of attainment of peak metamorphic conditions and subsequent ⁴⁰Ar/³⁹Ar closure during cooling. Modelling is consistent with the proposition that regional variations in timing and peak conditions of metamorphism are the result of the variable depths to which rocks were loaded by an eastward‐thickening thrust‐nappe pile rooted to the east (New Hampshire Sequence), as well as by diachronous structural processes within the lower plate rocks of the Vermont Sequence.     

Sedimentologic and palynologic records of the last deglaciation and Holocene from Ballston Lake, New York

Continuous pollen and sediment records from two ∼8.5-m-long cores document late Pleistocene and Holocene sedimentation and vegetation change in the Ballston Lake basin, eastern New York State. Pebbles at the base of both cores and the geomorphology of the watershed reflect the presence of the Mohawk River in the basin prior to ∼12,900 ± 70 cal yr B.P. Ballston Lake formed at the onset of the Younger Dryas (YD) by an avulsion of the Mohawk River. The transition from clay to gyttja with low magnetic susceptibility (MS), low bulk density, and high organic carbon indicates rapid warming and increased lake productivity beginning 11,020 cal yr B.P. MS measurements reveal that the influx of magnetic particles, associated with pre-Holocene clastic sedimentation, ceased after ∼10,780 cal yr B.P. The pollen record is subdivided into six zones: BL1 (12,920 to 11,020 cal yr B.P.) is dominated by boreal forest pollen; BL2 (11,020 to 10,780 cal yr B.P.) by pine (Pinus) forest pollen; BL3 (10,780 to 5290 cal yr B.P.) by hemlock (Tsuga) and mixed hardwood pollen; BL4 (5290 to 2680 cal yr B.P.) by mixed hardwood pollen; BL5a (2680 cal yr B.P. to 1030 cal yr B.P.) by conifer and mixed hardwood pollen; and BL5b (1030 cal B.P. to present) by increasing ragweed (Ambrosia) pollen. A 62% decrease in spruce (Picea) pollen in <320 cal years during BL1 reflects rapid warming at the end of the YD. Holocene pollen zones record more subtle climatic shifts than occurred at the end of the YD. One of the largest changes in the Holocene pollen spectra began ∼5300 cal yr B.P., and is characterized by a marked decline in hemlock pollen. This has been noted in other pollen records from the region and may record preferential selection of hemlock by a pathogen or parasites.     

A record of Holocene environmental and ecological changes from Wildwood Lake,Long Island,New York

Analyses of pollen, charcoal and organic content in a lake sediment core from Wildwood Lake, Long Island, New York, provide insights into the ecological and environmental history of this region. The early Holocene interval of the record (ca. 9800–8800 cal. a BP) indicates the presence of Pinus rigida–Quercus ilicifolia woodlands with high fire activity. A layer of sandy sediment dating to 9200 cal. a BP may reflect a brief period of reduced water depth, consistent with widespread evidence for cold, dry conditions at that time. Two other sandy layers, bracketed by ¹⁴C dates, represent a sedimentary hiatus from ca. 8800 to 4500 cal. a BP. This discontinuity may reflect the removal of some sediment during brief periods of reduced water depth at 5300 and 4600 cal. a BP. In the upper portion of the record (<4500 cal. a BP), subtle changes at ca. 3000 cal. a BP indicate declining prevalence of Quercus–Fagus–Carya forests and increasing abundance of Pinus rigida, perhaps due to reduced summer precipitation. Elevated percentages of herbaceous taxa in the uppermost sediments represent European agricultural activities. However, unlike charcoal records from southern New England, fire activity does not increase dramatically with European settlement. These findings indicate that present‐day Pinus rigida–Quercus ilicifolia woodlands on eastern Long Island are not a legacy of recent, anthropogenic disturbances. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface-structure-controlled sectoral zoning of the rare earth elements in fluorite from Long Lake, New York, and Bingham, New Mexico, USA

The concentration and distribution of rare earth elements (REE) in sectorally zoned fluorite crystals from Long Lake, New York, and the Hansonburg Mining District, Bingham, New Mexico, have been studied using cathodoluminescence and synchrotron X-ray fluorescence microanalysis (SXRFMA). In cubo-octahedral samples from Long Lake, New York, Ce, Nd, Gd, Dy, Ho, Er, and Tm are preferentially partitioned into the |111| sector relative to the |100| sector. Partition coefficients (K_d = concentration in |111| sector/concentration in |100| sector) range between 3.5 for Ce, to 1.4 for Tm, with a general decrease in K_d as elements deviated from the ionic radius of Ca²⁺, for which REE substitute in fluorite. Diffusion of the REE has occurred, as evidenced by gradual changes in composition over distances of 0.2 to 0.3 mm at sector boundaries.In Bingham samples, three different partition coefficients were determined for Dy: K_d|100|/|111| = 2.83, K_{d |100|/|110|} = 1.77, and K_{d |110|/|111|} = 1.60. These are mean K_d values for a 95% confidence interval. In another sample from the same deposit, Dy, Er, and Gd were found to be preferentially incorporated into the |100| sector relative to the |210| sector with average K_{d |100|/|210|} of 3.1, 2.4, and 2.9, respectively. In a third sample, Nd was found to be preferentially incorporated into the |110| sector relative to the |321| sector with an average K_{d |110|/|321|} value of 2.3.Compositional heterogeneities in a given sector (concentric zoning) have been resolved using SXRFMA but are significantly less than the concentration difference across sector boundaries. Often fluorite exists in a wide variety of morphologies, as is the case in the Hansonburg Mining District of Bingham. We suggest caution when using the REE as petrogenetic indicators because fluorite trace element chemistry can vary greatly among crystals within a deposit depending on the internal morphology of a particular crystal.     

Pressure, temperature and cooling rates of granulite facies migmatitic pelites from the southern Adirondack Highlands, New York

Detailed petrographic analysis was performed on samples from five localities within the southern Adirondacks. Textures and zoning patterns in garnet from all samples provide evidence for dehydration melting of biotite. Zoning of grossular in garnet – providing a record of prograde growth – shows both increasing and decreasing trends in garnet from the same sample. However, Ca concentrations at the garnet rims of most samples are identical (grossular = 3.4%). These observations have been interpreted as evidence for the differential timing of garnet nucleation and growth. All Fe/(Fe + Mg) and some spessartine distributions are consistent between samples, displaying diffusive profiles established largely upon cooling. Only one sample, in which retrogression was minimal, contains garnet with flat Fe/(Fe + Mg) profiles. A general pelitic pseudosection constructed in the system MnNCKFMASH reveals a maximum for Ca in garnet where the plagioclase‐out isopleth intersects the solidus (muscovite = 0). The pseudosection predicts bell‐shaped core‐to‐rim profiles of grossular during anatexis, similar to those observed in the rocks. Garnet–biotite thermometry and GASP barometry indicate peak temperatures of at least 790 °C at about 7–9 kbar, similar to conditions determined for the central Adirondacks. Cooling rates determined from finite difference modelling of spessartine and Fe/(Fe + Mg) diffusional profiles indicate a multi‐stage cooling history in which some period of rapid cooling (>200 °C Myr^?1) is required.     

Evolution of the barrier islands of southern Long Island, New York

Three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the Holocene transgression in southern Long Island, New York: (1) the Holocene transgressive stratigraphic sequence behind the present barriers, (2) the stratigraphic patterns of the inner shelf, and (3) the morphology of the now-buried late Pleistocene coastal features. The extensive preservation of backbarrier sediments, radiocarbon dated between 7000 and 8000 yr BP, on the inner shelf of southern Long Island suggests that the barriers have not retreated by continuous shoreface erosion alone, but have also undergone discontinuous retreat by in-place ‘drowning’ of barriers and stepwise retreat of the surf zone. Such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked. Based on the presence of submerged barrier sand bodies in seismic records, it is inferred that about 9000 years ago, when the sea stood about 24 m below the present sea level, a chain of barriers developed on the present shelf about 7 km offshore of the present barriers. With continued sea-level rise, the – 24 m barrier built upward until the sea reached about – 15 m MSL, just prior to 7000 yr BP. The barriers were then submerged by the rapidly rising sea, and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline. The surf zone overstepped to the landward margin of the old lagoon, which had become fixed at the steep seaward face of mid-Wisconsinan (?) or Sangamonian coastal barriers. During the past 5000 or 6000 years, the shoreface has retreated continuously by about 2 km. Evidence from southern Long Island and elsewhere in regions of coastal submergence indicates that rapid sea-level rise and low sand supply seem to favour the stepwise retreat of barriers, whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat. Stationary upbuilding, or seaward progradation of barriers may occur when supply of sand is great, and/or submergence is slowed or reversed. Morphologic highs on the pretransgression surface (such as old barrier ridges) tend to fix the migrating barrier shoreline during either continuous retreat, or stepwise retreat of barriers.     

Distribution of Pb between sediments and pore water in Woods Lake,Adirondack State Park,New York,U.S.A.

Interstitial water samples and sediments were collected from acidified Woods Lake (pH= 5.0) to evaluate Pb profile stability and distribution between the solid and aqueous phases. A simple equation was developed to describe the distribution coefficient for Pb(Kd_Pb), based on the sample moisture content and analyte concentrations in bulk sediment and pore water. In Woods Lake sediment Kd_Pb values ranged from 6.7 × 10⁴to6.7 × 10⁵ml/g. The affinity of Pb for the solid phase was further demonstrated by inverting a sediment core and leaving it for 10 months in situ. Upon retrieval, the Pb profile was found to have remained intact over the same depth, albeit inverted, as in the surrounding sediment. Geochemical modeling using MINTEQA2 demonstrates that Pb solids that may reasonably be expected to precipitate were all undersaturated by several orders of magnitude with respect to the interstitial water, indicating that Pb was sorbed to, rather than precipitated in, Woods Lake sediment.     

Interpretation of seismic and potential field data from western New York State and Lake Ontario

Lithoprobe and industry seismic profiles have furnished evidence of major zones of easterly dipping Grenville deformed crust extending southwest from exposed Grenville rocks north of Lake Ontario. Additional constraints on subsurface structure limited to the postulated Clarendon–Linden fault system south of Lake Ontario are provided by five east–west reflection lines recorded in 1976. Spatial correlations between seismic structure and magnetic anomalies are described from both Lake Ontario and the newly reprocessed New York lines.In the Paleozoic to Precambrian upper crust, the New York seismic sections show: (1) An easterly thickening wedge of subhorizontal Paleozoic strata unconformably overlying a Precambrian basement whose surface has an apparent regional easterly dip of 1–2°. Minor apparent normal offsets, possibly on the order of tens of meters, occur within the Paleozoic section. The generally poorly reflective unconformity may be locally characterized by topographic relief on the order of 100 m; (2) Apparent local displacement on the order of 90 m at the level of the Black River Group diminishes upward to little or no apparent offset of Queenston Shale; (3) Within the limited seismic sections, there appears to be no evidence that the complete upper crustal section is vertically or subvertically offset; (4) Dipping structure in the Paleozoic strata (15° to 35°) resembles some underlying Precambrian basement elements; (5) The surface continuity of inferred faults constituting the Clarendon–Linden system is not strongly supported by the seismic data.Beneath the Paleozoic strata, the seismic sections show both linear and arcuate reflector geometry with easterly apparent dips of 15° to 35° similar to the deep structures imaged on seismic lines from nearby Lake Ontario and on Lithoprobe lines to the north. The similarity supports an extension of easterly dipping Central Metasedimentary Belt structures of the Grenville orogen from southern Ontario to beneath western New York State.From a comparison of the magnetic and gravity fields with the New York seismic sections, we suggest: (1) The largely nonmagnetic Paleozoic strata appear to contribute negligibly to magnetic anomalies. Seismically imaged fractures in the New York Paleozoic strata appear to lie mainly west of a positive gravity anomaly. The relationship between magnetic and gravity anomalies and the changes in the geometry of interpreted Precambrian structures remains enigmatic; (2) North to northeast trending curvilinear magnetic and gravity anomalies parallel, but are not restricted to the principal trend of the postulated Clarendon–Linden fault system. Paleozoic fractures of the Clarendon–Linden system may partly overlie a southward extension of the Composite Arc Belt boundary zone.     

Grain-size sensitive deformation of a stretched conglomerate from Plymouth, Vermont

The finite strain of clasts (maximum aspect ratio varying from 2 to 40) in a deformed conglomerate from Dry Hill, Plymouth, Vermont, correlates inversely with the average grain size (300-150 μm) in the clast, suggesting that the operative deformation mechanism was grain-size sensitive. In a general way, the average quartz grain size appeared to be smaller in those clasts with higher volume of minerals other than quartz. Dislocation densities varied by as much as a factor of 10 from grain to grain within a clast, but the average dislocation density was relatively constant from clast to clast. If grain-size sensitivity of strength is accepted as a working hypothesis, other elements of the microstructure, such as grain flattening, grain morphology, and dislocation structure can be reconciled as happening either through a late, low strain, high stress pulse—if the current palaeostress indicators are correct to within a factor of 10 or as happening concurrently with the grain-size sensitive mechanism if the current palaeostress estimates are in error. The evidence from this study agrees with several previously published suggestions that grain-size sensitive deformation occurs in the crust for quartzose rocks with grain size of 100 to 300 μm at temperatures of 350 to 420°C.     

Distribution and significance of cordierite in paragneisses of the Hudson Highlands,southeastern New York

Cordierite occurs locally and sporadically in biotite-quartz-two feldspar paragneisses of the Precambrian Highlands complex in southeastern New York. Cordieritic and associated non-cordieritic gneisses were compared to determine the significance of cordierite for the metamorphic history of the complex.Microprobe analyses of the ferromagnesian phases show the following ranges in Fe/Mg (mol.): cordierite 0.19–0.43; biotite 0.33–0.73; garnet 1.98–3.56. Feldspar compositional ranges are: plagioclase An_25–53; K-feldspar in microperthite Or_62–87Ab_12–37 An_0–1. Garnet and plagioclase associated with cordierite are depleted in Ca relative to those in cordierite-free assemblages.Textural evidence, phase rule considerations and consistent distribution coefficients for FeO and MgO in coexisting garnet, cordierite and biotite from each locality examined suggest that all phases formed in at least local equilibrium during the hornblende-granulite subfacies metamorphism. The assemblages studied limit the conditions of metamorphism to between 700 and 750° C and 3.0 to 5.5. Kb. total pressure, with P _T greater than . Differences in mineral compositions and partitioning coefficients among the sampled areas suggest slight local differences within these ranges.Mineral and modal analyses of cordierite-bearing and cordierite-free gneisses show the latter to be enriched in calcium and potassium and depleted in alumina relative to the former. We conclude that the rarity of cordierite in the Highlands paragneisses reflects a scarcity of parent rocks of suitable composition rather than unfavorable physical conditions.     

Sedimentation rates in Fayetteville Green Lake, New York, U.S.A.

In Fayetteville Green Lake, past sedimentation rates can be accurately and precisely estimated by separating annual couplets or varves in dried sediment samples. Two measures were used, which serve as upper and lower limits on estimated sedimentation rate. They agree within 5 % with average annual sedimentation rate in couplets for recent years. Between 3 and 5 replicate samples are needed to reduce the half-width of 95 % confidence intervals on individual couplet sedimentation rates to 30 g m^?2 yr^?1 about 5 % of average recent rates. In the late 1800s sedimentation rate averaged 392 g m^?2 yr^?1 and ranged between 324 and 466 g m^?2 yr^?1, while in the 1970s the rate averaged 581 g m^?2 yr^?1 by the same measure, and ranged between 384 and 646 g m^?2 yr^?1. Sedimentation rate averaged for 13 years does not vary over short distances in the profundal zone, but lateral variation in sedimentation rate can be detected for individual years over the same distance. Not all this variation was associated with the non-uniform distribution of dark sublaminae and thin turbidites which cannot be separated from the annual layers. This indicates that although precise estimates of sedimentation rates can be made at different points in the lake, estimates will have to be made at numerous points before annual sedimentation rates for the lake as a whole can be accurately assessed.     

The REVEALS model,a new tool to estimate past regional plant abundance from pollen data in large lakes: validation in southern Sweden

The REVEALS model was developed to reconstruct quantitatively regional vegetation abundance (in a 10⁴–10⁵ km² area) from pollen assemblages in large lakes (≥100–500 ha). This model corrects for biases in pollen percentages caused by inter‐taxonomic differences in pollen productivity and dispersal. This paper presents the first case study to validate REVEALS, using empirical data from southern Sweden. Percentage cover of modern regional vegetation in Skåne and Småland, two contrasting vegetation regions, was predicted with REVEALS for 26 key taxa, using pollen assemblages from surface sediments in 10 large lakes, and compared to the actual vegetation within 10⁴ km² compiled from satellite data, forestry inventories, crop statistics, aerial photographs, and vegetation inventories. REVEALS works well in predicting the percentage cover of large vegetation units such as total trees (wooded land), total herbs (open land), total conifers and total broad‐leaved trees, and it provides reasonable estimates for individual taxa, including Pinus, Picea, Betula, Corylus, Alnus, Tilia, Salix spp., Juniperus, Poaceae, Cyperaceae, Cerealia and Secale. The results show great potential for REVEALS applications, including (1) quantitative reconstructions of past regional land cover important for palaeoclimatology and nature conservation, and (2) local‐scale reconstruction of vegetation (<1 km² up to ～ 5 km² area) relevant for palaeoecology and archaeology. Copyright © 2007 John Wiley & Sons, Ltd.     

A record of late Quaternary vegetation from Davis Lake,southern Puget Lowland,Washington

Pollen and macrofossil analyses of a core spanning 26,000 yr from Davis Lake reveal late Pleistocene and Holocene vegetational patterns in the Puget Lowland. The core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units. The late Pleistocene pollen sequence records two intervals of tundra-parkland vegetation. The earlier of these has high percentages of Picea, Gramineae, and Artemisia pollen and represents the vegetation during the Evans Creek Stade (Fraser Glaciation) (ca. 25,000–17,000 yr B.P.). The later parkland interval is dominated by Picea, Tsuga mertensiana, and Gramineae. It corresponds to the maximum ice advance in the Puget Lowland during the Vashon Stade (Fraser Glaciation) (ca. 14,000 yr B.P.). An increase in Pinus ontorta pollen between the two tundra-parkland intervals suggests a temporary rise in treeline during an unnamed interstade. After 13,500 yr B.P., a mixed woodland of subalpine and lowland conifers grew at Davis Lake during a period of rapid climatic amelioration. In the early Holocene, the prolonged expansion of Pseudotsuga and Alnus woodland suggests dry, temperate conditions similar to those of present rainshadow sites in the Puget Lowland. More-mesic forests of Tsuga eterophylla, Thuja plicata, and Pseudotsuga, similar to present lowland vegetation, appeared in the late Holocene (ca. 5500 yr B.P.).