U-series chronologies of the emerged coral limestone terraces on Barbados, West Indies, together with those of the terraces from New Guinea, have formed the basis for most late Pleistocene eustatic models. The so-called “Barbados sea level model” has been challenged in recent years, however. A major issue is whether during oxygen isotope stage 5e, when Rendezvous Hill reef complex on Barbados Island formed, the sea rose above the present position for one relatively brief period of <10,000 yr, or for two or more periods spanning approximately from 140,000 to 115,000 yr B.P. Evidence for the latter scenario has not come from initial studies of Barbados but from elsewhere; it is also inconclusive because of the dating uncertainties involved. We have carried out careful redeterminations of U-series ages on a suite of 29 Acropora palmata samples systematically collected from four of the lowest terraces on the island. Diagenetic disturbance may have caused the age spreads at some sampling outcrops. A model for the diagenetic exchange of uranium isotopes in coral samples with those in groundwater explains the anomalous 234U/238U ratios in samples with apparently unaltered mineralogy (aragonite) and trace element (Mg and Sr) chemistry. It shows that age dispersions of 5–10% can be engendered by a U exchange coefficient of the order of 10−6 yr−1. The lower-limit terrace ages, estimated from averaging the multiple measurements, are 81,000 ± 2000 yr (Worthing), 105,000 ± 1000 yr (Ventnor), 120,000 ± 2000 yr (Maxwell), and 117,000 ± 3000 yr (Rendezvous Hill). No evidence was found of previously inferred bipartite sea levels centering around 118,000 and 135,000 yr ago. This study documents the need of dating coral with the high precision/sensitivity mass-spectrometric techniques for future resolution of the temporal relationships among sea level changes, climate oscillations, and astronomical forcing—relationships originally addressed by the Barbados sea level model.

Amino acid and other studies have been made on the 30-km Pleistocene sections of the Intracoastal Waterway between Myrtle Beach and Little River, South Carolina. Our ratios differentiate the long-established Waccamaw (oldest), Canepatch, and Socastee formations. The ratios from the four laboratories that have worked in this area agree very well, and apparent conflicts with U-series dates may merely reflect an abundance of reworked corals. Our amino acid correlations with U-series coral dates in South Carolina, Bermuda, and the Mediterranean all argue that the classical Canepatch and its Horry Clay date from isotope stage 5e and not, as has been implied, from stage 7, 9, 11, or 13. Excavations and erosion have increased position-fixing problems along the Waterway, and “Canepatch” amino acid ratios and U-series dates (460,000 ± 100,000 yr B.P.) at “ICW5” may be from an older unit. The Canepatch shows the double marine transgression visible in many stage 5e deposits. Pollen shows that the second transgression occurred late in the interglaciation, and stratigraphic studies show that it reached 14 m. It therefore fits very well Antarctic ice-surge models of stage 5 sea level and climate. The Socastee adds to the evidence for one or more sea levels above 0 m late in stage 5.

Piston cores from the South Orkney Plateau penetrated overcompacted diamictons in water depths of up to 250 m. Detailed textural and petrological analyses of these diamictons indicate that they are basal tills. Seismic records from the plateau show a widespread surface of glacial erosion and provide additional evidence of an ice cap grounded to a depth of 250 m. Piston cores from the slope of the plateau penetrated diatomaceous muds resting directly on poorly sorted muds with very little to no biogenic material. The ice-rafted debris in these glacial-marine sediments is composed almost exclusively of material derived from the South Orkney Islands. This implies deposition beneath an ice shelf as opposed to iceberg rafting. In contrast, diatomaceous muds contain relatively abundant exotic iceberg-rafted material and reflect a glacial-maritime setting similar to that of today. The sharp contact separating diatomaceous surface sediments from basal tills and sub-ice shelf deposits indicates that the ice cap and ice shelf retreated from the plateau rapidly. Radiocarbon dates for diatomaceous muds from a glacial trough on the plateau indicate that the ice cap and ice shelf retreated from the plateau prior to 6000 to 7000 years ago. The homogeneity of surficial diatomaceous sediments suggests that sea ice conditions over the plateau have not changed radically since that time.

In an area north of the Giants Range in northeastern Minnesota the late Wisconsin glacial and extraglacial lithostratigraphy shows that, apart from one occurrence of red clayey till, the deposits can be related to the deglaciation of the Rainy Lobe, the margin of which retreated northward, leaving debris-rich ice behind. By a combination of pollen stratigraphy, lithostratigraphy, and chronostratigraphy of lake sediments in this area, together with multivariate numerical analyses of the data set, a “hiatus” stratigraphy was set up. Combined with the glacial and extraglacial stratigraphy, it shows that the area of Glacial Lake Norwood was possibly later filled with sediments, between masses of stagnant ice, following a damming of drainge in the south by the St. Louis Sublobe. The area was drained through the Embarrass channel when the St. Louis Sublobe retreated. Then followed the drainage of Lake Koochiching through the Embarrass channel. At ca. 10,200 14C yr B.P. the area apparently became free of stagnant ice as normal lake sedimentation began in all lakes studied. A lake-level rise is indicated ca. 1000 yr later. Apart from a long-lasting phase of birch tundra parkland between ca. 12,000 (or 11,500?) and 10,600 14C yr B.P., the general pollen stratigraphy fits into the regional picture with a more or less undisturbed and gradual plant immigration from the time of the culmination of the St. Louis Sublobe.

The most widespread of all Holocene tephra deposits in the Cook Inlet region of south-central Alaska is a set of deposits from Hayes volcano. Because of their unique phenocryst content—biotite in rare amounts and a high proportion of amphibole to pyroxene—the deposits are readily identifiable at all but the most distant sites where they are very fine grained. Eighteen radiocarbon dates from eight upland sites limit the age of the tephra set to between about 3500 and 3800 yr. The set originated at Hayes volcano in the Tordrillo Mountains 150 km northwest of Anchorage; seven or possibly eight closely succeeding deposits, low-silica dacite in composition, compose two main lobes that extend northeast for 400 km and south for at least 250 km from the vent. We estimate the total tephra volume to be 10 km3; multiple layers imply four to six larger and two or three smaller eruptions. The deposits are a nearly isochronous marker horizon that should be useful in future archeologic, geologic, and palynologic studies in the region.

Cosmogenically produced 3He in rocks can be used to date geomorphologic surfaces. Using the Late Pleistocene Bonneville flood event, the subsequent development of the Provo shoreline, and associated volcanic rocks, a production rate of 432 atoms/g/yr in olivine is determined for 38°56′ N latitude (present geomagnetic latitude 46.5°) at 1445 m altitude integrated over the last 14,400 years. Measurements of cosmogenic helium in flood deposits, on river-scoured surfaces, and lava flows show that it is possible to date directly large-scale events such as volcanic eruptions and catastrophic floods. Olivine and pyroxene are both satisfactory minerals for cosmogenic dating by the 3He method. However, in most cases, plagioclase and quartz are unsuitable because they do not quantitatively retain helium isotopes in their lattices.

The Stansbury shoreline, one of the conspicuous late Pleistocene shorelines of Lake Bonneville, consists of tufa-cemented gravel and barrier beaches within a vertical zone of about 45 m, the lower limit of which is 70 m above the modern average level of Great Salt Lake. Stratigraphic evidence at a number of localities, including new evidence from Crater Island on the west side of the Great Salt Lake Desert, shows that the Stansbury shoreline formed during the transgressive phase of late Pleistocene Lake bonneville (sometime between about 22,000 and 20,000 yr B.P.). Tufa-cemented gravel and barrier beaches were deposited in the Stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m. We refer to the fluctuations as the Stansbury oscillation. The Stansbury oscillation cannot have been caused by basin-hypsometric factors, such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin, or by changes in drainage basin size. Therefore, changes in climate must have caused the lake level to reverse its general rise, to drop about 45 m in altitude (reducing its surface area by about 18%, 5000 km2), and later to resume its rise. If the sizes of Great Basin lakes are controlled by the mean position of storm tracks and the jetstream, which as recently postulated may be controlled by the size of the continental ice sheets, the Stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the Laurentide ice sheet.

A lava flow in southern New Mexico extends into the Rio Grande Valley from the lower La Mesa geomorphic surface, a relict basin floor of middle Pleistocene age. Three buried soils occur beneath the lava at its east end. In places, the lava itself is buried by a sediment in which a soil has formed. Pedogenic carbonate was used to calculate the age of this soil, using a soil of lower La Mesa as a chronological guide. Both the latter soil and the Rio Grande Valley must be less than about 620,000 yr old according to dated volcanic ash, and are estimated to be about 500,000 yr old. Based upon this age and a total of 1200 kg/m2 pedogenic carbonate in the lower La Mesa soil, the carbonate accumulated at an average rate of about 2.4 kg/m2/1000 yr. Using the same rate of carbonate accumulation, the postlava soil took about 180,000 yr to form. However, not quite all of the pedogenic carbonate in this soil has been accounted for, and a general figure of 200,000 yr is suggested for its approximate age. The geological setting indicates that the age of the lava should be very close to the age of the postlava soil, and a general figure of 200,000 yr is also suggested for approximate age of the lava. This contrasts with a new K/Ar age of 490,000 ± 30,000 yr, which is considered to be too old. However, two previously obtained K/Ar ages of 232,000 ± 80,000 and 154,000 ± 119,000 yr are much closer to the estimate based on pedogenic carbonate. The landscape of the soil that buries the lava differs from the landscape of the lower La Mesa soil that was used as a chronological guide. The rate of carbonate movement into the soils could also differ, and for this reason the age obtained by pedogenic carbonate is considered tentative.

Most previous workers have regarded the insoluble residues of high-purity Quaternary limestones (coral reefs and oolites) as the most important parent material for well-developed, clay-rich soils on Caribbean and western Atlantic islands, but this genetic mechanism requires unreasonable amounts of limestone solution in Quaternary time. Other possible parent materials from external sources are volcanic ash from the Lesser Antilles island arc and Saharan dust carried across the Atlantic Ocean on the northeast trade winds. Soils on Quaternary coral terraces and carbonate eolianites on Barbados, Jamaica, the Florida Keys (United States), and New Providence Island (Bahamas) were studied to determine which, if either, external source was important. Caribbean volcanic ashes and Saharan dust can be clearly distinguished using ratios of relatively immobile elements (Al2O3/TiO2, Ti/Y, Ti/Zr, and Ti/Th). Comparison of these ratios in 25 soils, where estimated ages range from 125,000 to about 870,000 yr, shows that Saharan dust is the most important parent material for soils on all islands. These results indicate that the northeast trade winds have been an important component of the regional climatology for much of the Quaterary. Saharan dust may also be an important parent material for Caribbean island bauxites of much greater age.

Inasmuch as soils are open systems and rarely, if ever, achieve equilibrium with their environments, it is philosophically sound to view all soils as expressing varying levels of polygenesis as that term has been redefined. Soil genesis and resultant morphology may then be viewed in a comprehensive framework of soil evolution that consists of two linked pathways, one developmental and the other regressive, that reflect interactions of both exogenous and endogenous vectors (vectors are factors, processes, and conditions of pedogenesis). Following this philosophy, a model of pedogenesis is framed in an evolutional paradigm that emphasizes the integrated effects of dynamic and passive pedogenic vectors in directing pathways and in controlling rates of soil genesis through time. The dynamic vectors include energy and mass fluxes, frequencies of soil wetting and drying, water table dynamics, organisms, feedback processes, and pedoturbation. The passive vectors include parent materials, soil chemical environment, stability of geomorphic surfaces, and various evolved soil properties and conditions (accessions). Both sets of vectors vary spatially, and the dynamic vectors, more so than passive vectors, fluctuate through time. The model is expressed as S=f(D,P,dD/dt,dD/dt) where S is the state of the soil or degree of profile evolution, D is the set of dynamic vectors, P is the set of passive vectors, and dD/dt and dP/dt denote change through time t. The model helps explain the apparent minimal development and regressed character of some old soils and the rapid and strong development of some young ones.

A paleomagnetic record of secular variation has been obtained from a 17.4-m-long core drilled from loess in North Island, New Zealand. Three dated rhyolitic tephra occur in the loess core at depths of 1.5, 3.4,and 13.0 m, with ages of 22,500, ≧42,000, and 370,000 years, respectively. The base of the core is estimated to be 500,000 years old, which makes this the longest continuous loess sequence yet described from the Southern Hemisphere. Two periods of anomalously low inclination in the core are correlated with the Mungo Event (ca. 35,000 years ago) and the Emperor Event (ca. 490,000 years ago); the Blake Event (ca. 115,000 years ago) is not recorded.

Sediment features and soil patterns indicate that permafrost developed beyond the late Wisconsinan (Woodfordian) ice margin in Illinois. Vertical wedge-shaped bodies in Woodfordian glacigenic deposits and buried by Woodfordian loess are interpreted to be ice-wedge casts. Large-scale patterned ground, common on the late Wisconsinan drift plain and on the Illinoian drift plain to the south and west, also is interpreted to be the result of ice-wedge formation. Permafrost extended to about 38° 30′ N latitude and formed during the interval from about 21,000 to 16,000 yr B.P. Formation and degradation of permafrost was time-transgressive, directly related to the ice-marginal climate, and probably restricted temporally to less than 1000 years at a site. The following environmental conditions are suggested near the ice margin: mean annual ground temperature −3°C; mean annual air temperature −6 ± 2°C; less precipitation than modern, particularly in winter; strong and likely dry wind systems; and relatively open vegetation with few woody plants.

Postglacial geomorphic development of the Buchanan Drainage, a small tributary to the South Skunk River, is reconstructed by documenting relationships among four allostratigraphic units and 17 radiocarbon dates. Formation and headward expansion of the valley was both episodic and time-transgressive. Response to downstream conditions in the South Skunk River largely controlled the early formation of the basin. Downcutting through Pleistocene deposits produced a gravelly lag deposit that was buried by alluvium in the downstream portion of the valley during the early Holocene (10,500–7700 yr B.P.). Lag deposits formed in a similar manner continued to develop in the upper portion of the drainageway into the late Holocene (3000-2000 yr B.P.). Episodes of aggradation during the middle Holocene (7700-6300 yr B.P.) and late Holocene (3000-2000 yr B.P.) were separated by a period of soil formation. Holocene geomorphic events in the drainageway coincide with some vegetational and climatic changes as documented in upland pollen sequences from central Iowa. Analysis of plant macrofossil assemblages recovered from alluvium indicates that during the middle Holocene forest contracted and prairie expanded into the uplands within the basin. Vegetational changes within the basin apparently had only minor influence on rates of hillslope erosion, and the widely accepted relationship between prairie (versus forest) vegetative cover and increased rates of hillslope erosion did not hold. Instead, greater amounts of erosion occurred under forested conditions when local water tables were higher and seepage erosion was more effective.

Vegetation changes in the southeastern Great Basin between 17,500 and 8000 yr B.P. can be reconstructed from plant macrofossil assemblages in ancient packrat (Neotoma spp.) middens. Vegetation instability after ca. 16,000 yr B.P. involved a dispoportionate number of local immigrations (arrivals) relative to apparent local extinctions (departures). At a site in modern woodland, less than 50% of the arrivals were of transients, species that subsequently went locally extinct; but at a low-elevation desert site almost all arrivals before 10,000 yr B.P. were transient species. Thus, by the close of the last glacial age, higher elevations supported vegetation that resembled present woodland, while lower elevations supported desertscrub that bore little resemblance to modern thermophilous desertscrub.

Differences in the pace of plant community “modernization” in different elevational zones can be attributed to migrational lag. Woodland species survived the last glacial age at low elevations nearby, and began arriving at sites within current woodland before 11,700 yr B.P. Warm-desert plants were displaced far to the south, and began arriving after 9500 yr B.P. Moreover, their staggered arrival times suggest that low winter temperatures did not inhibit their migration during the early Holocene. These data suggest that biotic factors, particularly variable dispersal distances and consequent migrational lag, did affect deglacial vegetation change.

A paleoclimatic reconstruction for the past 35,000 years for northern Oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs. High-pH groundwaters (pH up to 11.9) discharge from the mantle sequence of the Oman Ophiolite as the product of modern, low-temperature serpentinization. Under arid climatic conditions, hyperalkaline discharge occurs at the surface. Uptake of atmospheric CO2 precipitates characteristic laminated travertines, accompanied by strong kinetic depletion of 13C and 18O. Pluvial climates supporting a shallow bicarbonate-groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite-replaced roots and stems. All such carbonates have modern initial 14C contents, allowing radiocarbon dating and paleoclimatic reconstruction for the late Pleistocene and Holocene. Our reconstruction shows a dominantly wet late Pleistocene up to 19,000 yr B.P., when a phase of climatic deterioration began, leading to a period of hyperaridity which dominated from ca. 16,300 to 13,000 yr B.P. The early Holocene pluvial occurred from 12,500 to ca. 6500 yr B.P. and was followed by renewed climatic deterioration and the current phase of hyperaridity. Comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the A'Rub al Khali of central Saudi Arabia and the summer insolation-driven monsoon record of east Africa and the Arabian Sea is remarkably good.

Fission-track ages of zircon crystals from four tuff layers in the late Cenozoic sediment sequence of the Boso Peninsula,.Japan, are 1.6 ± 0.2 myr (the Kurotaki Formation), 5.5 ± 0.6 and 5.2 ± 0.5 myr (the uppermost part of the Amatsu Formation), and 11.5 ± 0.8 myr (the middle part of the Amatsu Formation). These ages provide numerical age constraints on magneto-biostratigraphy. The normal polarity interval in the lower part of the Kiwada Formation corresponds to the Olduvai polarity subzone. The boundary between the Pliocene and Pleistocene lies slightly above the Olduvai polarity subzone.

Full-glacial pollen records from southeastern United States are composed primarily of pine and spruce, with lesser amounts of fir, birch, and oak. A simulation model of forest dynamics was used to reconstruct the composition and structure of these forests on the Delmarva Peninsula of Virginia, where pollen data were available to test the model, and climate and soils data were available to drive the model. Reconstructed annual precipitation and summer air temperature were consistent with modern analog estimates from the pollen record. Annual precipitation was also consistent with climates simulated by atmospheric general circulation models, but summers were colder. Correcting these simulated climates for possible errors resulted in summer air temperature consistent with our estimate. However, two alternative parameter sets relating simulated tree growth to air temperature sums precluded robust forest reconstructions. With one parameter set, the species dominating the simulated forests were not consistent with the pollen record. The other parameter set produced forests more consistent with paleoecological data, indicating that the climate was correct. These differences in simulated forest composition reflected inadequacies in the parameterization of air temperature effects in forest models.

Annual (October through September) precipitation from 1100 A.D. to modern times is reconstructed for Morocco, using Cedrus atlantica (Endl.) Carrière tree-ring chronologies. Both multiple regression on principal components and the bootstrap method are use to calibrate tree-ring width with precipitation; precipitation variation is reconstructed for three climatically distinct areas: the humid, subhumid, and arid regions of Morocco. A series of successive wet and dry periods is identified for the past 1000 years; the maximum length of the 13 dry periods (during which precipitation was at least 1σ below normal) is 6 years. Twenty-one years are identified during which precipitation fell more than 2σ below normal. We are unable to identify significant correspondence in climatic variation in Morocco, Europe, and the Sahel during this time period.

Late-glacial macrofossils from a 10-m core from Alpine Swamp, New Jersey, were radiocarbon dated using accelerator mass spectrometry (AMS). The arrival of the first trees to the area following deglaciation is indicated by maximum percentages of spruce pollen and a date of 12,290 ± 440 yr B.P. on a single spruce needle. Subsequent spread of deciduous hardwoods was followed by the expansion of boreal taxa, including spruce (Picea), fir (Abies), larch (Larix laricina), paper birch (Betula papyrifera), and alder (Alnus). Three AMS dates on paper birch seeds and a spruce needle during this boreal expansion indicate that it took place between 11,000 and 10,000 yr B.P. The timing of this vegetational shift and its correlation with late-glacial pollen stratigraphy from many sites in southern New England indicate that a climatic reversal correlative with the Younger Dryas characterized the North Atlantic seaboard of the United States.

Two distinct elevations of emerged notches can be recognized on the southeastern coast of Vanua Levu: the higher notch is +2.22 to +3.30 m above low-tide level and the lower +1.52 to +1.65 m above low-tide level. Many emerged Holocene corals encrust higher notch floors and benches or occur as microatolls and from these radiocarbon ages ranging from 6000 to 3400 yr B.P. were obtained. The higher notches are significantly higher than present high-tide level, even allowing for relative tectonic uplift. This is supported by elevations of emerged microatolls and their 14C ages. Thus, mean sea level of the mid-Holocene was higher than that at present.