Three atomic mass spectrometry (AMS) dates have been obtained for shell material from the bottomset beds of a glaciomarine delta at Spencers Island, Nova Scotia, near the head of the Bay of Fundy. The sediments in the delta are part of the previously undated Five Islands Formation, and are the first direct indictaion of the age of deglaciation in this region. The dates range from 14,300 to 12,600 yr B.P. and record the duration of deposition of a diamicton under the deltaic deposits and of the delta itself. The diamicton may have formed around 14,000 yr B.P. under ice-shelf or calving-bay conditions, or by a readvance of grounded ice. The Spencers Island delta is part of a prominent ice-marginal stand marked by numerous deltas along the Minas Basin. The time of formation of the deltas and the inferred ice margin is between 13,500 and 12,000 yr B.P. based on the Spencers Island dates and palynologically confirmed dates on the base of lake-sediment cores from the delta surface. Ice-marginal glaciomarine deposits near St. John, New Brunswick, record a range of radiocarbon dates similar to the Spencers Island dates. This implies that the Bay of Fundy became virtually ice free about 14,000 yr B.P.

A time-series of tree-ringwidth indices for alpine timberline foxtail pine (Pinus balfouriana) from the Sierra Nevada of California shows a growth response to summer, late fall, and early winter temperatures that is the inverse of that resulting in the expansion of alpine glaciers. These are correlated with lichen-dated moraines and avalanche deposits that accumulated during subsequent decades. Minima in the ringwidth record, reflecting marked temperature declines occurred at 810, 1470, 1610, 1700 and 1810. Cold periods of lesser extent are also indicated between 1190 to 1400 and suggest that the initial pulses of the Sierran Matthes advances may have begun as early as 1190, or 150 yr earlier than previously dated. The Matthes advances were preceded by a period of pronounced warmth from 900 to 1190 during which timberline rose 10 m to its present elevation. A warm period is also indicated between 1500 and 1580. Recent work extending the tree-ring chronology to 3031 yr B.P. and radiocarbon dating of weathered samples to 6300 yr B.P. suggests that the chronology may ultimately be applicable to the dating of earlier Sierran glacier advances.

The geochronology of a gravity core collected from an anoxic, high sedimentation rate (>2.5 cm/yr) setting near the head of the Saguenay Fjord in Quebec has been established for the period 1900–1979 to a resolution of better than 1 yr using a constant flux 210Pb model. Interannual variations of the sedimentation rate of between 28 and 50% are caused by rapid inputs of coarse silt and fine sand during spring freshet events. A significant correlation between sand percentage and sediment accumulation rate reflects the increase in stream competence during the spring freshet; the sand percentage parameter can be used in conjunction with sediment size parameters to estimate temporal variations in river discharge intensity. Between 1914 and 1979 sediment accumulation rates were about 60% higher during the spring and summer compared to fall and winter seasons. Both the magnitude of the Saguenay River spring discharge and the quantity of precipitation stored as snow decrease through the 20th century suggesting that the freshet intensity was governed largely by natural rather than anthropogenic (e.g., dam construction) factors. A direct correlation between sand flux, peak river discharge, and a snow storage parameter provides a link between sediment texture and climate. Detailed analyses of the grain-size distributions for dated core intervals offer a method for the reconstruction of a proxy record of paleodischarge for the Saguenay River spring freshets.

Relatively complete stratigraphic records of the Bonneville cycle and of at least one and probably two earlier lacustrine are exposed along the Bear River below Cutler Dam in northern Utah between altitudes of 1290 and 1365 m. In most exposures the unconformity between the Bonneville Alloformation and the underlying unit, herein named the Cutler Dam Alloformation, is marked by slight erosional relief and by a weakly to moderately developed buried soil, herein named the Fielding Geosol. In truncated profiles, the Fielding Geosol reaches a maximum of stage II carbonate morphology. Wood from near the base of the Cutler Dam Alloformation yielded a 14C date of >36,000 yr B.P. (Beta-9845). Alloisoleucine/isoleucine (aIle/Ile) ratios of Sphaerium shells from the Cutler Dam beds average 0.15 ± 0.01 in the total hydrolysate, which is significantly greater than the average for Sphaerium shells of Bonneville age elsewhere in the basin. Therefore, the Cutler Dam Alloformation is older than 36,000 yr B.P., but much younger than deposits of the Little Valley lake cycle (140,000 yr B.P.?) which bear shells having significantly higher aIle/Ile ratios. The Cutler Dam Alloformation along the Bear River may be broadly correlative with marine oxygen-isotope stages 4 or 3. Fine-grained, fossiliferous, marginal-lacustrine facies of the Cutler Dam Alloformation are exposed at altitudes near 1340 m, and are probably the highest exposures of sediments deposited in the early or middle Wisconsin lake in the Bonneville basin.

Radiocarbon and thermoluminescence (TL) age-determinations have been obtained for a large Pleistocene alluvial terrace on the Nepean River near Sydney, New South Wales, Australia. The deposit was laid down by a braided river system prior to the last glacial maximum. Six thoroughly pretreated samples of charcoal and degraded wood buried within gravels at the base of the terrace yielded apparent 14C ages of ∼37,000–42,000 yr B.P. These compare favorably with four TL determinations that gave apparent ages of ∼41,000–47,000 yr B.P. for the same deposit. Adjustment of the 14C ages to take geomagnetic effects into account further improves the correlation between these two independent dating techniques. In addition, 14C and TL correctly identified a reworked portion of the fine-grained alluvial overburden as being substantially younger than the main body of the terrace. These results augur well for the usefulness of TL age determinations of certain alluvial deposits.

Evidence for climatic change is found in petrographic thin sections from soils formed on glaciofluvial deposits of Rock Creek and the lower Clarks Fork, Montana. These soils, presently in a semiarid climate, range from late Pliocene to Holocene in age, and have undergone periodic fluctuations in soil moisture caused by climatic changes. In the lower parts of soil B horizons, accretion of illuvial layers of clay (argillans) occurs mainly during wet (glacial) climatic periods, whereas carbonate precipitates mainly during dry (interglacial) climatic periods. Thin-section studies of the argillan and carbonate layers show that: (1) post-Pinedale soils that have formed only in the present interglacial climate contain areas of secondary carbonate unrelated to argillans, (2) soils formed on outwash of successively older glaciations contain proportionately more alternating layers of argillans and carbonate, and (3) the maximum number and sequence of layers in a soil correspond to the number of local cycles of glacial-outwash deposition and subsequent stream incision that followed the beginning of soil formation. These cycles are inferred to correspond to local glacial-interglacial fluctuations. The correspondence between the microscopic record and the glacial-outwash record for Rock Creek suggests that some of the climatic changes seen in the marine oxygen-isotope record did not strongly affect the study area.

Radiocarbon dates indicate a Farmdalian through Woodfordian age for fossil white spruce (Picea glauca) in the Tunica Hills, a greater time span than previously documented. These dates, furthermore, require revision of the ages of fluvial terrace deposits in the region. Spruce-bearing Terrace 1 sediments, previously regarded as late Woodfordian to Holocene age, are of Farmdalian to late Holocene age. Terrace 2 sediments, previously assigned a Sangamonian or Farmdalian age, are of probable Altonian age. Plant fossils in Terrace 1 sediments represent two climatically and temporally distinct assemblages: a cool-temperate, Farmdalian-Woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak-hickory association; and a warm-temperate Holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the Tunica Hills. Locally, fossils of white spruce have been reworked into younger Terrace 1 sediments containing the warm-temperate plant assemblage. The transition from the cool-temperate flora to the modern warm-temperate flora in the Tunica Hills probably occurred around 12,000 yr B.P.

Sediment, pollen, and plant macrofossil stratigraphies from two small oligotrophic Chamaedaphne-Sphagnum peatlands provide data about local hydrologic changes in northern Michigan during the Holocene. Gleason Bog started about 8000 yr B.P. as a shallow pond that supported rich fen vegetation. After it was partly filled with peat and sand (about 4000 yr B.P.), the vegetation changed to oligotrophic bog. At Gates Bog paludification starting about 3800 yr B.P. caused peat accumulation over sand without an initial pond phase. The onset of peat accumulation at both sites is attributed to a rise in the water table resulting from the onset of cool and moist late Holocene climates. The water table of Gleason Bog is linked to the water level of adjacent Douglas Lake, which may have undergone a simultaneous rise. The results emphasize the individuality of hydrological conditions and hydroseral development in northern Michigan peatlands.

Detailed study of gastropods recovered from the Lake Theo Site, Briscoe County, Texas, has revealed a progressive decline in species diversity from early Holocene to the present. Knowledge of the microhabitats preferred by the recovered species allows a partial reconstruction of environments required to produce such communities. Since the early Holocene, the Lake Theo area has experienced a progressive loss of deciduous riparian gallery woodland habitat. Alteration in plant communities was caused by a dramatic decrease in effective precipitation. Analysis of the sequence of local extirpation of the various snail species indicates that the decrease in precipitation and increase in temperature probably were not concurrent.

The extinct Harrington's mountain goat (Oreamnos harringtoni Stock) is predominantly known from dry cave localities in the Grand Canyon, Arizona, in addition to two sites in the Great Basin, Nevada, and from San Josecito Cave, Nuevo Leon, Mexico. A dry shelter in Natural Bridges National Monument, on the central Colorado Plateau, southeastern Utah, preserves numerous remains of the extinct mountain goat in addition to pack rat middens. Remains from a 100-cm stratigraphic profile indicate that O. harringtoni lived on the plateau >39,800 yr B.P., the oldest directly dated find of extinct mountain goat. Plant macrofossils indicate that Engelmann's spruce (Picea engelmannii), limber pine (Pinus flexilis), rose (Rosa cf. woodsii), and Douglas fir (Pseudotsuga menziesii) grew during the late Pleistocene where a riparian and a pinyon-juniper (Pinus edulis-Juniperus osteosperma) community now predominates; Douglas fir are found only in mesic, protected, north-facing areas. Limber pine, Douglas fir, bark, and grasses were the major dietary components in the dung. A springtime diet of birch (Betula) is determined from pollen clumps in dung pellets.