Magnetic susceptibility profiles χ(z) in loess sequences reflect a combination of two climatically modulated processes: dust deposition and pedogenic development. Prominent soils with high χ values, for example, likely reflect periods of slow dust deposition, and warm wet conditions favorable for rapid chemical weathering. To refine our understanding of the climate records contained in loess, we develop a numerical model as a tool for exploring quantitatively the integrated record of the temporal variation in rates of loess aggradation and soil development contained in χ profiles. In our model, the aggrading loess is pedogenically altered in a reactive zone near the ground surface. The strength of the χ signal is dictated by both the depth-dependent intensity of pedogenic processes and the rate of dust accumulation, which dictates the total time a loess parcel spends in the near-surface reactive zone. The model can accommodate both pedogenic production of magnetically susceptible minerals and arrival of magnetically susceptible grains as eolian dust. To explore the model performance and develop a sense of time and length scales implicit in χ profiles, we first examine simple synthetic cases with idealized steady and cyclic climatic forcing. Reported χ profiles in three Chinese loess sequences at varying distances from the western China dust source are then modeled in two illustrative ways: (i) by imposing a specific dust deposition rate history that is proportional to the dust accumulation rate history reported from western Pacific deep-sea cores, allowing the time variation of pedogenic rates to be calculated directly from χ profiles; and (ii) by imposing both dust accumulation and pedogenic rate histories that are independently scaled by the deep-sea δ18O history, which reflects global climate cycles to which regional climate forcing is linked. We find that the zone of pedogenic activity is roughly 0.5–1.0 m thick, both deposition rate and pedogenic intensity have varied dramatically over the last 140,000 yr, the age structure of the Luochuan loess sequence is best fit by driving the model with the δ18O record, and environmental conditions must have been anomalously favorable for pedogenesis during isotope stage 3 at all three sites. Finally, we advocate the assembly of a variety of data types at a suite of sites within any loess field that taken together will better constrain the temporal and spatial patterns of climatically modulated deposition and pedogenic processes.

Five pre-Illinoian tills are recognized and named informally in northern Missouri, near the southernmost margin of the pre-Illinoian Laurentide ice sheet. The three youngest tills (McCredie formation) have high (50–60%) expandable clay mineral contents and normal remanent magnetic polarity. The next oldest till (Moberly formation) has low (30–40%) expandable clay content and reversed polarity. The oldest till (Atlanta formation) has very low or no expandable clay minerals. Its remanent magnetic polarity is unknown.

The sequence of four pre-Illinoian tills above the Atlanta formation probably correlates with the similar sequence of four pre-Illinoian “A type” tills in western Iowa and eastern Nebraska. The upper four tills in Missouri are also correlated, in order of increasing age, with the three members of the Wolf Creek Formation and the older Alburnett Formation in eastern Iowa. The oldest till in Missouri possibly correlates with the “C type” till in western Iowa.

Pre-Illinoian Laurentide ice reached the same approximate southern margin at least five times. Those advances deposited tills which maintain characteristic compositions over distances of at least 350 km along flow lines.

A chronology of alluvial surfaces on piedmont slopes below the western Ajo Mountains, southern Arizona, has been obtained using cosmogenic 36Cl accumulation and AMS radiocarbon dating. The apparent 36Cl ages of individual boulders range from 520,000 to 13,000 yr, and the 14C ages of organic material in the two young terraces are 2750–2350 and 17,800 cal yr B.P. The sequence of36Cl ages is consistent with the apparent stratigraphic order, but groupings of similar ages for different surfaces appear to result from repeated reworking of older surfaces associated with the deposition of younger ones. The youngest surface gave a distribution of 36Cl ages about 30,000 yr older than the 14C and soil ages; however, this distribution had36Cl ages that overlapped with 36Cl ages from active channels and hillslopes. We attribute the older-than-expected exposure ages of sampled boulders to inheritance of 36Cl while residing near the surface during very slow erosion on the mountain front. Our results show that although cosmogenic nuclide accumulation can help establish chronologies for surfaces in piedmont settings, care must be used in evaluating the effects of complex exposure histories.

Mature desert pavements are traditionally regarded as hallmarks of stability, but their stability is dynamic, not static. In a study aimed at documenting this dynamic stability and its role in healing surface disturbances, experiments were performed over a 5-yr period on small cleared patches, or plats, on pavement surfaces in Panamint Valley, California. These experiments show that stones from plat edges begin to resurface the clearing at rates of about 1% per year on 40-cm-square plats and 10% per year on 10-cm-square plats. Stones contributing to the regenerated pavement have smaller average diameters than stones on the surrounding pavement. Cavities 5–10 cm deep, formed in mature pavement by removal of embedded boulders, fill by ravel and slope failure. After five years, cavity depth has been reduced by as much as 60%. Forty-year-old boulder cavities are nearly completely refilled and have been repaved by smaller than average pavement stones. Gaps caused by removal of small stones (2–3 cm) have completely healed in 5 yr. Displacement of surface stones by small animals is a major component of the healing process.

Fluvial, marine, and mixed fluvial-marine deposition on the coastal plain of Hanalei Bay on the north shore of Kauai, Hawaii, records a middle- to late-Holocene fall of relative sea level. Radiocarbon dating of the regression boundary preserved in the stratigraphy of the coastal plain documents a seaward shift of the shoreline beginning at least 4800–4580 cal yr B.P. and continuing until at least 2160–1940 cal yr B.P. Marine sands stranded in the backshore and coastal plain environment are buried by fluvial floodplain and channel sands, silts, and muds. In places, erosion at the regression contact exposed older marine sands thus increasing the hiatus at the regression disconformity. The shoreline regression is best explained as the result of a fall in relative sea level. The age and elevation of the cored regression boundary at sites that have not been influenced by erosion are consistent with a middle- to late-Holocene highstand of relative sea level as predicted by geophysical models of whole Earth deformation related to deglaciation.

Pleistocene glacial-estuarine sediment deposited in an intertidal environment of northeastern Bristol Bay, southwestern Alaska, was dated using a variety of approaches, including infrared stimulated and thermoluminescence (IRSL and TL) techniques. Analysis of modern and 14C-dated Holocene tide-flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation, thereby lending confidence to ages obtained from similar Pleistocene deposits by luminescence techniques. IRSL seems to be especially well suited for dating, with resolution on time scales of <10,000 yr. The ages of tide-flat mud of the Nushagak Formation, derived from the Ahklun Mountains to the northwest of Bristol Bay, and of Halfmoon Bay drift, derived from the Alaska Peninsula to the southeast, suggest contemporaneous glacial-estuarine deposition related to independent glacial source areas about 75,000–80,000 yr ago. This age is consistent with other geochronological data that indicate a pre-late-Wisconsin and post-substage-5e age, including nonfinite 14C ages, a lack of interglacial indicators, and Old Crow tephra (∼140,000 yr) atop the drift, normal paleomagnetic inclinations, and amino acid (isoleucine) epimerization ratios (aIle/Ile). AIle/Ile ratios in Portlandia arctica(0.052 ± 0.003) from a marine-lag horizon at South Naknek beach, which separates Halfmoon Bay drift above from older glacial-estuarine drift below, are only slightly higher than in Mya truncata(0.041 ± 0.007) from last-interglacial Pelukian deposits at Nome. As laboratory heating experiments show that the two genera epimerize at similar rates, these data imply correlation of the marine lag at South Naknek beach with Pelukian deposits. Hence, glaciers on the Alaska Peninsula experienced major pre-late-Wisconsin advances both before and after the last interglaciation. Shells reworked into Halfmoon Bay drift yield aIle/Ile ratios of 0.028 ± 0.005 for Portlandiaat Second Point and 0.027 ± 0.001 for Hiatella arcticaat Etolin Point. Together with assumptions about the postdepositional temperature history, these ratios indicate that the shells are at least 55,000 yr, and probably closer to ∼90,000 yr, although the uncertainty in this age estimate is broad. The amino acid and luminescence data converge on an age between about 75,000, and 90,000 yr, late during oxygen-isotope stage 5, for a major ice advance far beyond late-Wisconsin limits.

The vegetation and climate of the Pampa grassland, Argentina, during the late Quaternary are reconstructed from pollen recovered from dated stratigraphic sections from arroyo walls and from archaelogical excavations. Prior to 10,500 yr B.P., herbaceous psammophytic steppe existed in the central part of the Pampa grassland while xerophytic woodland associated with psammophytic and halophytic steppe occurred in the southwestern part of the Pampa. These types of vegetation and the continental conditions that prevailed in the area of the present-day coast (38°S), indicate subhumid-dry climate and annual precipitation 100 mm lower than present. A subsequent change toward a vegetation characteristic of ponds, swamps, and foodplains, or toward environments with locally more effective moisture, occurred ca. 10,500 yr B.P. suggesting annual precipitation close to modern levels or a higher availability of water in the central part of the Pampa grassland, this type of vegetation existed until 8000 yr B.P., when it was replaced by grassland communities that lasted until 7000 yr B.P. In the southwestern part of the Pampa grassland, this vegetation developed before 7000 yr B.P. and persisted until ca. 5000 yr B.P. Sea level higher than the present ca. 6200 yr B.P. is consistent with sharp modification of the vegetation and development of local halophytic communities dominant at 38°S. A return to subhumid-dry conditions occurred after 5000 yr B.P. The late Holocene vegetation is characterized by pollen assemblages similar to the psammophytic and halophytic communities of the Southern pampa grassland, associated with communities with more edaphic conditions. At the same time, at 38°S a sea level regression is suggested by the dominance of fresh-water pollen assemblages and micropaleontological remains. The trend toward humid, temperate conditions ca. 1000 yr B.P. suggested by vertebrate remains characteristic of temperate and humid conditions, as well as a very short but dry episode during the 18th century suggested by the geology, are not clearly evidenced in the pollen sequences. Vegetational and climatic changes are explained by the latitudinal shifts and changes in intensity of the southern atmospheric circulation and changes in sea level.

Physical and chemical coupling of peatland vegetation, soils and landforms, and atmosphere creates feedbacks which may be important in ice-age initiation. A box diffusion CO2 exchange model shows that a transient forcing of 500 Gt C (the amount proposed to have accumulated in peatlands during the last interglacial–glacial transition) over 5000 yr results in a lowering of atmospheric CO2 by about 40 ppm. Proxy data indicate that a decrease in atmospheric CO2 may have occurred over the last 5000 yr up to preindustrial times, and the amount is similar to that calculated from Holocene peatland expansion (∼22 ppm). These results suggest that models should consider the role of peatlands in ice-age initiation.

Pikas (Ochtona)—small gnawing mammals, related to rabbits—range today throughout parts of the Northern Hemisphere, but had a wider distribution during the Pleistocene. Nine caves from northeastern North America (a region not occupied by pikas today) have Pleistocene deposits containing remains of Ochotona. We examine 526 fossil specimens (ranging in age from approximately 850,000 to 8670 yr B.P.) from five of these caves. Two morphological forms of Ochotona lived in northeastern North America during the late Pleistocene—a large species (probably O. whartoni) and a small species (probably O. princeps).Ochotona of glacial age are not necessarily indicative of talus slopes and mesic communities. O. princeps-like of the Irvingtonian of West Virginia were living with an amphibian-reptilian assemblage found in the area today, implying winters not much, if at all, colder than at present. Late glacial and postglacial change in climate south of the ice sheets in effect would have isolated Ochotona in eastern North America, where they were unable to retreat to the west or north. Whereas western pika had the option of moving up in elevation, into boreal islands, eastern forms became restricted to ever-diminishing habitats, culminating in extinction and extirpation. Radiocarbon ages imply that Ochotona lived in eastern North America during the late Pleistocene (late Rancholabrean) and into the earliest Holocene. We describe the youngest remains of Ochotona in eastern North America and the youngest for the extinct large form, O. whartoni.