Direct information on the isotopic composition and timing of the now-vanished Laurentide glacier can be found in subglacial calcite or in early diagenetic concretions from glaciolacustrine deposits. Th/U isotopic measurements on early diagenetic concretions frome Lake Deschaillons varves (St. Lawrence Lowland, Québec) date the early Wisconsinan major ice advance at ca. 80,000 yr (isotopic stage 5a/4 transition). Significant retreat occurred at ca. 46,000 yr (isotopic stage 3) as indicated by Th/U isochrones on early diagenetic concretions from Lake Gayhurst varves in the Appalachian foothills of Québec. During the maximum extension of the ice, which is dated at ca. 22,000 yr by Th/U measurements on subglacial calcite at Cantley (northern margin of the St. Lawrence Lowland), δ18O values (vs PDB) ranging from −16/−19‰ (surficial ice) to ca. −30‰ (basal ice) are inferred for the Laurentide ice isotopic composition. Superimposition of two phases of carbonate precipitation does not prevent the establishment of their respective age and isotopic composition through correlation of independent parameters and calculation of mixing lines.

Twenty samples of artifactual ostrich eggshell and hearth charcoal, firmly to loosely associated with basinal lacustrine, playa, and sand sheet sediments in the Dakhleh Oasis region of south-central Egypt, yield radiocarbon ages between ca. 8800 and ca. 4700 yr B.P. The sediments record variable sedimentary responses to an early Holocene pluvial interval in this virtually rainless region. Differences of hydrogeology and morphometry among and within basin types complicate paleoclimatic interpretation.

Discovery in 1980 of Camp 18 of the 1930 Bagnold expedition in northwestern Sudan has resulted in an exceptionally long record of barchan movement from which an average rate of 7.5 m/yr has been calculated. Measurements of the rate of dune advance since 1980 have not varied significantly, indicating a state of quasiequilibrium exists. The dune field is moving over an undulating sand sheet exhibiting various stages of Holocene pedogenesis and containing Neolithic sites. The sand sheet overlies Pleistocene alluvium with stronger stages of pedogenesis. All of these deposits may be a significant source of dune sand. Wind-blown grass fragments trapped by advancing slipfaces mark former slipface positions and indicate late Holocene rainfall events, which can be radiocarbon dated. Parabolic forms (revealed by SPOT images) at the windward ends of the dune fields are transitional to barchans, suggesting sand accumulation in vegetation germinated during a Holocene wet period. In addition, sand streaks from sand-sheet undulations suggest that active eolian erosion of sand sheets contributes to the sand supply of dune fields. Pedogenesis during pluvial periods contributes to silt and clay fractions of bimodal sand sheet sediments. From wind streaks on LANDSAT images and an estimated average rate of dune advance, positions of dune fields during past hyperarid periods can be estimated.

A sequential method for quantitative identification of sediment source components, based on magnetic measurements, has been developed and tested for sediments from the Rhode River, Maryland. Simulated mixing tests and multiple regression were employed to establish numerical relationships between source component proportions and the magnetic measurements of mixtures. On the basis of these multivariate mixing models, source components of three estuarine sediment cores were estimated by linear programming. The results strongly support the previous studies on this catchment which indicated a dramatic change in sediment source some 150 to 200 yr ago. Quantitative calculations are more useful and informative than purely qualitative descriptions.

The Pilliga Sandstone region of the northwest slope of New South Wales has a natural vegetation cover of sclerophyllous relatively closed to open forests with a largely heathy understorey, and a warm, subhumid and continental climate. Pollen analysis of spring-fed deposits gives a vegetation history extending from at least 30,000 yr B.P. to the late Holocene. Tree pollen became scarce after about 25,000 yr B.P. and an assemblage dominated by Chenopodiaceae, Liguliflorae, Tubuliflorae, and probably Poaceae developed. No similar assemblage is known from present pollen rain studies carried out in Australia. However, it clearly represents a treeless open shrub-steppe formation and therefore an arid or semiarid environment. The site thus provides evidence of an eastward late Pleistocene extension of the arid zone in Australia, and is the first full-glacial vegetation record between 20° and 35° latitude in Australia. The present vegetation cover did not become reestablished until the beginning of the Holocene, which raises questions about the form in which Pilliga Sandstone vegetation survived full-glacial conditions.

Pedogenically significant chemical extracts of iron, aluminum, and phosphorus are related mainly to time in chronosequences from Baffin Island (Canadian Arctic), the alpine Sierra Nevada and Wind River Range (western United States), the alpine Khumbu Glacier area (Himalaya, Nepal), and the alpine Southern Alps (New Zealand). Based on the accumulation index for Fe and Al, and the depletion index for P in each region, the following ranking of chemical pedogenic development is obtained: Southern Alps > Khumbu Glacier area ≅ Wind River Range > Sierra Nevada > coastal Baffin Island > inland Baffin Island. The ranking mainly follows regional climate, with the greatest accumulation and depletion to the warmest and wettest environment, and the least accumulation and depletion in the coldest and driest environment.

Radiocarbon dating of bulk sediments has been the standard method for establishing chronologies in the studies of lake sediment cores which have contributed significantly to our knowledge of late Quaternary paleo-environments. These bulk sediment dates are presumed to be direct ageindicators for the speciments (e.g., pollen or macrofossils) which are actually being studied. However, several recent studies have reinforced long-standing apprehensions concerning this presumption. In this study, we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry. The dates obtained by this method should provide more reliable radiocarbon chronologies for paleo-environmental studies than have been obtainable by bulk sediment dating.

Skeletal remains of Homo erectus found in Pleistocene loess at two sites near Lantian in central China are of greatly different geologic age. The cranium found in the fossil-bearing strata at Gongwangling is about 1.15 myr old whereas the remains found at the Chenjiawo locality in middle Pleistocene loess are about 0.65 myr old. The dating is based on new paleomagnetic polarity determinations and on the lithostratigraphic position of the fossils in the loess-paleosol sequence. Our results confirm that both localities are older than the first occupation of Zhoukoudian. New dates, palaeoenvironmental settings, and morphological features of the hominids from Lantian localities have significant bearing on the understanding of adaptive radiations of the middle and late hominids in Asia.

Extensive patches of fossil shell deposits are found in many places along the rims of emerged coastal embayments and lagoon floors on the southern coast of Sri Lanka. Compositional and depositional sequences of fossil shells (Veneridae, Cerithidae, and Nassaridae) reveal that the bulk of the valves has been accumulated by three processes: (a) the shells have been piled up on the rims of emerged coastal embayments mainly by wave action; (b) following coastal progradation since the late Subboreal the shells possibly gathered on lagoon floors; and (c) the valves on the coastal hilly areas and dune areas were discarded by early human inhabitants in the course of their daily activities. Radiocarbon dates of fossil corals along the southwest and south coasts support this interpretation and indicate that mean sea level was at least 1 m higher than present in the middle Holocene. The fossil species may have lived in an intertidal zone of embayments and lagoons that extended 3 km or more inland form the present shore in the middle Holocene.

Diatom assemblages from modern West African rivers and from lacustrine sediments subjected to deflation represent the present-day sources of continental diatoms to the sea. Diatom productivity in large rivers is high, especially for the genus Melosira. Windblown diatoms derive mainly from the central and northern Sahara (summer dust plume) where saline chloride-water assemblages are widespread, or from the southern edge of the Sahara (winter dust plume) where Melosira-rich assemblages of dilute water predominate. Freshwater diatom peaks in Atlantic cores may reflect (1) phases of increased river influx, correlated with humid episodes on the continent or (2) phases of enhanced deflation and wind transport during arid episodes (the single hypothesis for fine sediments from mid-ocean sites). Genus Melosira dominates the freshwater assemblages of many modern and fossil marine samples, whatever the transport agent is. Therefore, it is not an accurate paleoclimate indicator by itself, but associated taxa may provide information on the environmental and geographical origin of the displaced diatoms. This tentative approach shows that freshwater diatoms in Atlantic cores may be a good tool for reconstructing paleoclimates and for establishing continent-ocean correlations if species analyses are made and if the continental distribution of the taxa encountered is considered.