The rivers of central Australia rise in the MacDonnell Ranges and flow out across broad, low-relief plains into the surrounding desert. The stratigraphy of the Ross River plain records the areal extent and frequency of Holocene floods. This floodout plain is underlain by deeply weathered alluvial deposits, characterized by red earth soils dated by thermoluminesence at >59,000 yr. This old alluvium is covered by a sheet-like deposit of very silty sand of probable eolian origin dated by thermoluminesence at 9200 ± 900 yr. The oldest Holocene alluvium occurs as broad, low-relief bars and levee deposits flanking the modem channel and as low-relief long-wavelength bedforms that fan out across the plain. This deposit resulted from a flood flow, up to 10 km wide, that covered the entire plain. Evidence for several large floods between 1500 and 700 yr B.P. is also preserved in a 500- to 1500-m-wide paleochannel. Thus, the surface features on the floodout plains are the product of a few rare large flood events. This paleohydrologic record is additional evidence of the dynamic nature of the hydrometerological regime of central Australia.

A new record from Potato Lake, central Arizona, details vegetation and climate changes since the mid-Wisconsin for the southern Colorado Plateau. Recovery of a longer record, discrimination of pine pollen to species groups, and identification of macrofossil remains extend Whiteside's (1965) original study. During the mid-Wisconsin (ca. 35,000-21,000 yr B.P.) a mixed forest of Engelmann spruce (Picea engelmannii) and other conifers grew at the site, suggesting a minimum elevational vegetation depression of ca. 460 m. Summer temperatures were as much as 5°C cooler than today. During the late Wisconsin (ca. 21,000-10,400 yr B.P.), even-cooler temperatures (7°C colder than today; ca. 800 m depression) allowed Engelmann spruce alone to predominate. Warming by ca. 10,400 yr B.P. led to the establishment of the modern ponderosa pine (Pinus ponderosa) forest. Thus, the mid-Wisconsin was not warm enough to support ponderosa pine forests in regions where the species predominates today. Climatic estimates presented here are consistent with other lines of evidence suggesting a cool and/or wet mid-Wisconsin, and a cold and/or wet late-Wisconsin climate for much of the Southwest. Potato Lake was almost completely dry during the mid-Holocene, but lake levels increased to near modern conditions by ca. 3000 yr B.P.

Quantitative estimates of late-Quaternary climate in the northeastern United States are reconstructed from fossil pollen data to evaluate changes in the regional moisture balance inferred from water-level fluctuations. We use environmental response surfaces to calibrate modern pollen data (for 17 different taxa) to an index of effective soil moisture and mean annual precipitation. We apply these response surfaces to fossil pollen data from 60 sites in the region to reconstruct changes in soil moisture and mean annual precipitation at 3000-yr intervals from 12,000 yr B.P. to present. The mapped reconstructions of soil moisture and mean annual precipitation illustrate how the regional moisture balance of the Northeast may have changed over the last 12,000 yr in response to changing climate. Reconstructions of annual precipitation show a gradual increase from 30% below modern values at 12,000 yr B.P. to near-modern values by 6000 yr B.P. and then remain relatively constant thereafter. Reconstructed changes in the index of effective soil moisture, however, show a pattern of near-modern values at 12,000, 6000, and 3000 yr B.P., with significantly lower values estimated for 9000 yr B.P., the time of maximum pine pollen abundances in the Northeast. This pattern of change is similar to the change in regional moisture balance inferred from stratigraphic records of water-level fluctuations. These results confirm previous interpretations, based on records of water-level fluctuations, that conditions in the Northeast were significantly drier during the early to middle Holocene than at other times during the last 12,000 yr.

A Holocene deglaciation sequence for the Windmill Islands was determined from the 14C age of raised marine shorelines, lakebottom sediments, and Adelie penguin remains found in abandoned rookeries. A north-south gradient in the elevation of the upper marine limit was observed, with the highest marine limit (31-32 m) observed on Browning Peninsula and Hull Island at the southern edge of the islands. Correspondingly, the southern islands were found to have been deglaciated by 8000 (corr.) yr B.P. while the northern islands were deglaciated by 5500 (corr.) yr B.P. Isostatic uplift rates were calculated as 0.5 to 0.6 m/100 yr, with an estimated total uplift of around 53 m which indicates late Pleistocene ice sheet thicknesses of 200 and 400 m over the islands and adjacent Petersen Bank, respectively. The margin of the Late Pleistocene grounded ice sheet extended an estimated 8-15 km offshore which coincides with the location of the 200 m isobath.

New detailed pollen analysis of the lower part of the Upper Pliocene Semaforo section (Crotone, Italy) documents cyclic behavior of vegetation at the beginning of the Northern Hemisphere glaciations. The competition between four vegetation units (subtropical humid forest, deciduous temperate forest, altitudinal coniferous forest, and open xeric assemblage) probably reflects modifications of vegetation belts at this montane site. Several increases in herbaceous open vegetation regularly alternate with subtropical humid forest, which expresses rapid climatic oscillations. The complete temporal succession—deciduous forest (rich in Quercus), followed by subtropical humid forest (Taxodiaceae and Cathaya), then altitudinal coniferous forest (Tsuga, Cedrus, Abies, and Picea), and finally herbaceous open vegetation (Graminae, Compositae, and Artemisia )—displays the climatic evolution from warm and humid interglaciation to cold and dry glaciation. It also suggests an independent variation of temperature and humidity, the two main climatic parameters. The vegetation history of southern Calabria recorded in the Semaforo section have been correlated with the ∂18O signal established in the Atlantic Ocean.

Postglacial uplift in the eastern Hudson Bay area is among the most rapid in the world (300 m during the last 8000 yr). Although emergence curves based on 14 C-dated raised shorelines give a consistent basis for modeling relative sea-level changes, such a low-resolution dating method is inappropriate for estimating trends over recent decades. A major downward displacement of white spruce (Picea glauca (Moench) Voss) and tamarack (Larix laricina (DuRoi) K. Koch) occurred on protected shores as a response to shoreline retreat during this century. Analysis of the age distribution of trees indicates a progradation of white spruce and tamarack on gently sloping terrain ranging from 1.3 and 2.6 cm/yr, respectively, toward the sea. Improvement of climatic conditions during the 20th century favored such expansion which was probably faster than the real land emergence rates, but recent episodes of high water levels caused regression of forest margins over the highly exposed shores. Nevertheless, the downward trend of the treeline over this century substantiates the projections of 14C-dated coastal emergence curves during the modern period (1.0 to 1.3 cm/yr) by providing an estimate of the maximum rates of shoreline retreat.

Earlier attempts to date the Taung hominid type specimen of Australopithecus africanus Dart yielded conflicting results. Recent faunal studies pointed to an age of 2.3 myr. Radioisotopic results suggested 1.0 myr. New uranium studies reveal that the Thabaseek (the oldest Taung tufa) was not a closed system and that younger uranium entered the tufa after initial deposition, producing an apparent isotopic age younger than the age of deposition. The Thabaseek isotopic dates provide only a terminus ad quem and this technique is therefore not applicable to the older Taung tufas. Delson's dating (2.3 myr) of cercopithecoids from Hrdlicka's pinnacle ca. 50 m from the hominid site provides the best available approximation to the age of the hominid. In our new Taung excavation, stratigraphic analysis indicates that the hominid may somewhat predate most identified fauna. Sedimentologically the hominid matrix proves to be of fluvial deposition, and hence closely resembles one Hrdlicka deposit, both samples differing appreciably from all other Taung samples which bespeak eolian deposition. Thus, the conditions under which the hominid-bearing stratum was deposited were virtually identical to those pertaining to one of the Hrdlicka deposits. The newest results show that Taung was not the youngest South African australopithecine site and eliminate the discrepancy between the relative ages of the Taung A. africanus africanus and the Sterkfontein A. africanus transvaalensis.

The malacofaunas of Burgundy, France, reflect changes in climate and the activities of man during the Holocene. Statistical analyses based on the Shannon diversity index and correspondence analysis are used to describe the mollusk assemblages in a composite sequence based on three well-dated sites. The variation demonstrated by the mollusks suggests that a two-step warming took place between 10,000 and 9000 and 8000 and 6000 yr B.P. in relative agreement with the timing of the deglaciation in the tropical Atlantic Ocean proposed by Mix and Ruddiman (1985, Quaternary Science Reviews 4, 59-108). High humidity, partly associated with widespread inundations of the valleys between 10,000 and 8000 yr B.P., may be related to estimated variations in the rate of freshwater discharge to the Atlantic Ocean reported by Fairbanks (1989, Nature 342, 637-642). The increasing impact of human activities on the environment during the past 2000 yr is indicated by the low diversity of the mollusk assemblages, demonstrating the need for careful interpretation of the youngest Holocene sediments in this region.

Sediments of 13 piston cores from opposite continental slopes of the South China Sea, off southern China and Sabah (northern Borneo), were analyzed by sedimentological methods and dated by oxygen isotope stratigraphy. Sediments mostly consist of hemipelagic clay with 20% carbonate off Sabah and 40% off China. We calculated terrigenous and carbonate accumulation rates for up to 11 time-slices from the Holocene to oxygen-isotope stage 6. Terrigenous accumulation rates generally increase with water depth and reach a maximum at the middle slope off Sabah and at the lower continental slope off China. During glacial and interglacial times this distribution pattern did not markedly change, despite an increase of accumulation rates for glacial periods by a factor of 2 to 5 compared to interglacial periods. Rates are negatively correlated with positions of sea level, which controls the partition of fluviatile terrigenous material for deposition on shelf, slope, and abyssal plain. Carbonate accumulation rates are higher off China by a factor of 2 compared to Sabah, probably indicating higher calcareous plankton productivity.

Paludified dune fields in southern Québec provided a unique opportunity to analyze a mid-Holocene forest succession, ranging from xero-mesophilous forests to treed peatlands, which registered the hemlock decline, a major biostratigraphic event in eastern North America. Our fossil-tree chronology established from 66 radiocarbon dates of tree stems indicates that white pine and hemlock were present at the study site about 6000-5700 yr B.P. Hemlock reached a maximum 4900-4800 yr B.P. and then declined between 4600 and 3800 yr B.P.; the species recovered around 3700 yr B.P. and then decreased when white pine and eastern latch dominated the site after 3000 yr B.P. and between 2600 and 2200 yr B.P., respectively. Tree-ring signatures of fossil hemlocks suggest the continuous influence of biotic factors, possibly insect defoliators, throughout the record, as shown by recurrent suppressed-growth pattern. Microscopic examination of the hemlock fossil stems disclosed no evidence of fungal disease. The hemlock decline was probably caused by regional posthypsithermal climatic changes, toward moister conditions.

A fossil assemblage containing molluscs, ostracodes, and fish has been recovered from lacustrine sediments from near Connersville, southeastern Indiana. The reversed remanent magnetic signature of the sediments and the extent of isoleucine epimerization in molluscan shell protein indicate a pre-Illinoian age for the fossils. The fauna includes four taxa of fish, Coregonus sp., cf. Prosopium sp., cf. Thymallus arcticus, and Catostomus sp.; four taxa of ostracodes, Cytherissa lacustris, Candona caudata, Cyclocypris ampla, and Candona sp.; and 28 taxa of molluscs. Elements of the aquatic molluscs, fish, and ostracodes suggest a cool-water lake (8° to 16°C). The terrestrial molluscs include boreal species that now reach the southern limits of their range in the Great Lakes region near the north shore of Lake Superior and imply average summer temperatures of about 15°C near the lake margins. The lake may have been formed when West Lebanon ice advanced into the Anderson-New Castle Buried Valley system which drained northwest as a tributary of the Lafayette Bedrock Valley System.

A 5000-yr stratigraphic record containing fossil pollen, charcoal, and bones of the extinct Quaternary megafauna from Andolonomby, a hypersaline pond in arid southwestern Madagascar, shows evidence for climatic desiccation beginning about 3000 yr B.P. Pollen spectra shift at this time from primarily arboreal taxa characteristic of forests and woodlands of more mesic western Madagascar, to wooded savanna typical of somewhat drier localities. Between 3000 and 2000 yr B.P., the site became increasingly arid. Charcoal and pollen evidence indicates that increased fire and disturbance occurred at the site beginning ca. 1900 yr B.P., probably signaling the beginning of human settlement in the area. The fossil record suggests that various human and natural factors on the island may have interacted in the subsequent millennium to culminate in the extinction of the entire endemic megafauna.

Pollen and charcoal analysis of a 5.6-m sediment core from Lago de las Morrenas (9°29′N, 83°29′W; 3480 m) provides evidence of postglacial vegetation and fire history in the highlands of the Cordillera de Talamanca, Costa Rica. The site is presently surrounded by treeless páramo vegetation and apparently has been so since deglaciation about 10,000 yr B.P. Pollen spectra suggest no pronounced changes in vegetation since ice retreat. Fires set by people or lightning have burned the páramo repeatedly, with fire activity probably highest during the late Holocene, but these fires have not carved páramo from forest. Pollen percentages for Gramineae and other páramo taxa decline upward, whereas percentages for certain subalpine, lower montane, and lowland forest taxa increase slightly; these changes may reflect the impact of prehistoric human activity or slight upslope migrations of forest taxa owing to climatic warming. There is no clear evidence of higher timberlines during the mid-Holocene.

The faunas found in the mountains of central Irian Jaya have experienced dramatic changes through the late Quaternary. Remains of two previously unknown species of large marsupial, Maokopia ronaldi and Protemnodon hopei, have been recovered from unrelated cave and fluvial deposits which today occur in dense upper montane forest. Direct dating of the finds has not as yet been possible, but stratigraphic, sedimentologic, and palynologic evidence indicates that these species lived near a climatic treeline in subalpine grassland in the late Pleistocene. At higher altitudes a rockshelter provided the second known mid-Holocene record of Thylogale christenseni and Thylogale sp. cf. brunii, apparently extinct grassland wallabies. The two largest remaining subalpine mammal species are being locally exterminated by hunting, leaving only a large murid, Mallomys gunung, which weighs less than 2.0 kg. The area thus records the disappearance of a grassland-adapted fauna. The possum Pseudocheirops cupreus dominates in modem hunting returns, although this species is totally absent from the local fossil records. It may thus be in the process of invading a vacated and disturbed niche from the upper montane forest.

Interpretation of a 1.5-m mid- to late- Wisconsinan stratigraphic sequence containing fossil vertebrates from the Animal Fair Site in Dry Cave, Eddy County, New Mexico, suggests a progression of habitats, all cooler and moister than today. Mid-Wisconsinan semiarid, moderately warm grasslands or grassy woodlands initially were replaced by cooler, more mesic, grassy woodlands; these were followed by cool, relatively dense sagebrush-grassland-woodland with elements from mixed-coniferous forest. A minor reversal of trend toward earlier, warmer conditions appears at the top of the section. Species collected from each level were basically harmonious until climatic deterioration, documented by invasion of new biotic elements at the end of the mid-Wisconsinan, permitted incursion of taxa associated with more boreal areas; these replaced most of the local fauna but failed to dislodge several taxa with southern affinities.