Palynological data from sediment cores from the Ruby Marshes provide a record of environmental and climatic changes over the last 40,000 yr. The modern marsh waters are fresh, but no deeper than ∼3 m. A shallow saline lake occupied this basin during the middle Wisconsin, followed by fresh and perhaps deep waters by 18,000 to 15,000 yr B.P. No sediments were recovered for the period between 15,000 and 11,000 yr B.P., possibly due to lake desiccation. By 10,800 yr B.P. a fresh-water lake was again present, and deeper-than-modern conditions lasted until 6800 yr B.P. The middle Holocene was characterized by very shallow water, and perhaps complete desiccation. The marsh system deepened after 4700 yr B.P., and fresh-water conditions persisted until modern times. Vegetation changes in Ruby Valley were more gradual than those seen in the paleolimno-logical record. Sagebrush steppe was more widespread than at present through the late Pleistocene and early Holocene, giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr B.P. Shadscale steppe contracted by 4000 yr B.P., but had greater than modern coverage until 1000 to 500 yr ago. Pinyon-juniper woodland was established in the southern Ruby Mountains by 4700 yr B.P.

A paleomagnetic record for the Grande Pile lacustrine sequence deposited during the last interglacial-glacial cycle has been constructed based on continuous sampling (n = 792) of a 15-m-long oriented core (GPXX). The NRM intensity, magnetic susceptibility, and saturation isothermal remanent magnetization show pronounced variations related to the climatic zonations in the sequence. The stratigraphic consistency of the paleomagnetic directions vary considerably due to variations in signal/noise ratios. Paleosecular variation patterns occur throughout most of the core, as well as several zones of inferred geomagnetic excursions. The application of magnetic fabric (AMS) shows that some apparent Lanterne (Weichselian) excursions reside in deformed sediments, while anomalous paleomagnetic directions in the 70,000 to 120,000 yr B.P. time interval appear in sediments with low signal/noise ratios and a high degree of compaction. The signature is hence not likely to reflect genuine records of geomagnetic field variations in these levels. Discrepancies between the magnetostratigraphy of GPXX and a previously investigated core implies that the earlier claimed regional correlations based on the paleomagnetic signature of low intensity levels should be critically reassessed. The Grande Pile sequence is not regarded as a magnetostratigraphic standard for the last interglacial-glacial cycle.

Thermoluminescence (TL) dating was applied to seven samples of siliceous fluvial sands from the East Alligator River of Northern Australia, giving ages ranging from modern to 6000 yr B.P. Two methods of estimating the equivalent dose (ED), total bleach and regenerative, were applied to the 90- to 125-μm quartz fraction of the samples in order to determine the reliability and internal consistency of the technique. High-resolution γ and α spectroscopy were used to measure radionuclide contents; these measurements revealed an excess 226Ra activity compared with 230Th. This excess decreased with depth, and was used directly to derive mean sedimentation rates, and thus sediment ages. Both this method and one 14C date confirmed the validity of the TL values, which increased systematically with depth and were consistent with site stratigraphy. TL was of limited use in the dating of these late Holocene deposits because of age uncertainties of 500 to 1600 yr, resulting from a significant residual ED. This residual probably resulted from incomplete bleaching during reworking upstream of the sampling site. For Pleistocene deposits, the residual ED will be less significant because of higher total EDs, and TL dates will be correspondingly more accurate.

An understanding of the response of a fluvial system to past climatic changes is useful for predicting its response to future shifts in temperature and precipitation. To determine the response of the Columbia River system to previous climatic conditions and transitions, a well-dated sequence of floodplain development in the Wells Reservoir region was compared with the paleoenvironmental history of the Columbia River Basin. Results of this comparison indicate that aggradation episodes, occurring approximately 9000-8000, 7000-6500, 4400-3900, and 2400-1800 yr B.P., coincided with climatic transitions that share certain characteristics. The inferred climates associated with aggradation had at least moderate rates of precipitation that occurred mainly in winter coupled with moderate winter temperatures. Such conditions would have resulted in the buildup of snowpacks and a high frequency of rain-on-snow events. The warming and precipitation increases predicted for the Pacific Northwest under most CO2-doubling scenarios are likely to repeat these conditions, which could increase the frequency of severe, sediment-laden floods in the Columbia River Basin.

Flights of tectonically uplifted, late Quaternary marine terraces are preserved at several localities along the Oregon coast. Intervening coastal areas without marine terraces reflect net subsidence. These gaps in the coastal terrace record make it difficult to correlate terraces along the Pacific coast. To test the utility of soils in relative dating and correlation, two flights of marine terraces near Cape Blanco and Cape Arago were investigated. The terraces could be distinguished in each area from soil morphological properties and a quantitative index of soil development derived from field descriptions. The soils in the two areas show a progression in development from spodosols to spodosols underlain by clayey material to ultisols. The lowest two terraces at Cape Blanco, which have reported age estimates of 80,000 and 105,000 yr, are correlative with the lowest two terraces at Cape Arago. The fifth and oldest terrace at Cape Blanco has no equivalent at Cape Arago. Soil development indices for the third and fourth terraces at each area allow two alternative sets of correlations.

Pollen assemblages from a 6.6-m exposure of Pleistocene lake silt in central western New York consist of anomalous mixtures dominated by spruce, pine, and sedge but with a significant representation of deciduous forest elements. Leaves of Dryas integrifolia and plants of the terrestrial moss Distichium from the lake silt yielded AMS ages of 24,900 ± 1000 and 24,180 ± 900 yr B.P., indicating that the silt was deposited during the middle Wisconsinan Plum Point interstade and that the pollen of beech, hickory, and other deciduous trees was recycled from an interglacial deposit. Caution therefore must be exercised in the paleoecological interpretation of interstadial lake deposits. Plant macrofossil assemblages (seeds, fruits, mosses) from the silt also probably are mixtures of primary and secondary fossils. Scanning electron microscopy of surface features of fruits and seeds revealed two classes of preservation. The best-preserved fossils had intact surface microfeatures and are considered of primary origin. Those with the outer cell layer degraded or absent probably have been recycled. The distributions of species represented in the latter category center on the Great Lakes region and southward, whereas those of the primary fossils are more northern and indicate tundra and spruce-jack pine forest. The late Wisconsinan Kent ice margin advanced across central western New York after ca. 24,500 yr B.P. into a mosaic of tundra and conifer forest.

Pollen analysis and five radiocarbon dates of a 687-cm core provide a detailed chronology of environmental change in a marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea-level rise during the early history of the marsh. From ca. 7000 to 4500 yr B.P. the site was a freshwater marsh, trees were more abundant than today, and grassland was the regional vegetation. As sea level rose, salt marsh gradually invaded the site. Brief periods of freshwater marsh 3800, 2800, 2300, and after 560 yr B.P. correlate with episodes of global cooling during the Neoglacial. The historic period is marked by the appearance of exotic species (particularly Erodium cf. cicutarium and Eucalyptus) and the spores of fungi (Sporormiella and Thecaphora). Peak influx of pollen, spores, and charcoal probably reflect greater frequency of flooding and erosion ca. 5000 yr B.P. and during the last 1000 yr.

Cold-adapted beetles colonized the lowlands of the Lake Region of south-central Chile following the retreat of glaciers from their maximum extent at about 19,500 yr B.P. The beetle fauna from 18,000 to 14,000 yr B.P. was characterized by species of moorland habitats. This fauna was species-poor compared to later faunas of the postglacial interval. By 14,000 yr B.P. arboreal species were replacing species of open habitats, reflecting a change toward a warmer climate. By about 12,500 yr B.P. fossil beetle assemblages consisted entirely of rain forest species. The fauna of the postglacial interval was about five times as species-rich as that of the glacial interval. The change in species composition and greater diversity of the beetle fauna was produced by an increase in mean annual temperature estimated to be about 4°–5°C. This was the last major climatic change to affect profoundly the biota of the middle latitudes of South America. The fossil beetle assemblages do not imply a reversal to a colder climate at the time of the European Younger Dryas interval between 11,000 and 10,000 yr B.P.

Effective hydration temperature (EHT) is essential for the computation of obsidian hydration dates. In the Atacama Desert, the scarcity of air-temperature records combines with extremes of elevation and local temperature to encourage, or even require, the use of buried thermal cells to record on-site mean annual temperatures. Compositional analysis (sourcing) and hydration rate development in the laboratory are also necessary, especially where other dating methods are unavailable to confirm the hydration rate. Paleoindian or Early Archaic through modern obsidian dates support a human settlement pattern history derived from archaeological/geomorphological studies of climatological and hydrological change.