Age data for about 660 speleothems and about 140 spring-deposited travertines were collected, including many unpublished results. These data were plotted as histograms and also as error-weighted frequency curves on a 350,000-yr scale. These plots clearly show periods of increased speleothem/travertine growth as well as times of cessation. The periods of most frequent speleothem growth were between approximately 130,000 and 90,000 yr ago and since about 15,000 yr ago. Such periods before 150,000 yr ago, however, cannot be yet recognized because of a lack of sufficient data and the associated uncertainties of dates in this age range. A comparison with the oxygen-isotope record of deep-sea core V28–:238 shows a clear relationship, indicating that terrestrial calcite formation is controlled by paleoclimatic fluctuations. The evident climatic stimulation of Quaternary calcite formation is readily explained geochemically and is substantiated by the obvious difference in speleothem/travertine growth as a function of geographic position.

Variations of ice-sheet volume during the Quaternary ice ages are simulated using a simple ice-sheet model for the Northern Hemisphere. The basic model predicts ice thickness and bedrock deformation in a north-south cross section, with a prescribed snow-budget distribution shifted uniformly in space to represent the orbital perturbations. An ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level. The model produces a large ∼ 100,000-yr response in fair agreement (correlation coefficient up to 0.8) with the δ18O deep-sea core records. To increase confidence in the results, several of the more uncertain model components are extended or replaced, using an alternative treatment of bedrock deformation, a more realistic ice-shelf model of ice calving, and a generalized parameterization for such features as the North Atlantic deglacial meltwater layer. Much the same ice-age simulations and agreement with the δ18O records, as with the original model, are still obtained. The model is run with different types of forcing to identify which aspect of the orbital forcing controls the phase of the 100,000-yr cycles. First, the model is shown to give a ∼ 100,000-yr response to nearly any kind of higher-frequency forcing. Although over the last 2-million yrs the model phase is mainly controlled by the precessional modulation due to eccentricity, over just the last 500,000 yr the observed phase can also be simulated with eccentricity held constant. A definite conclusion on the phase control of the real 100,000-yr cycles is prevented by uncertainty in the deep-sea core time scales before ∼600,000 yr B.P. The model is adapted to represent West Antarctica, and yields unforced internal oscillations with periods of about 50,000 yr.

Rock varnish coats many surfaces of geomorphic and archaeologic interest in arid lands. All varnish dating techniques are limited by the time lag between the exposure of a surface to subaerial processes and the onset of varnishing. They are valid only where manganese is not remobilized after deposition, for example, in most arid environments. The premise of a new age-determination method, cation-ratio dating, is that the ratio of the more mobile cations (e.g., K and Ca) to titanium in varnish decreases with time. Although there are many inherent assumptions and potential limitations, cation-ratio dating has been verified on relative age-sequences from a Death Valley debris cone, Negev Desert talus flatirons, and prehistoric lake levels at Searles Lake in California. Varnish cation ratios have been calibrated to independently dated surfaces in the Coso volcanic field and vicinity in California. Tentative absolute dates have been assigned to geomorphic surfaces in the Coso area. Cation ratios have been used to distinguish relative ages of archaeologic artifacts in southwestern North America and to demonstrate that varnish at the South Stoddard locality, Mojave Desert, did not form in 25 yr.

Since 1965, ice-wedge casts have been reported in deposits of sand and gravel in Connecticut. These are wedge forms up to 1.1 m wide and many meters high. Most are single forms, not in polygonal array. They are found in adjoining states as well. Their distribution, dimensions, structure, and fabric and an assessment of the former physical environment preclude their origin as permafrost features. They appear to be tension fractures produced by the loading of coarse clastics on fine clastics near and below the water table where sediments creep toward a stream or depression. Locally movement started with kettle formation during deglaciation. However, some wedges cut horizontal layers of iron-coated sand and gravel and must be younger than those distinctly postglacial phenomena. Moreover, modern B horizons of the overlying soil have moved down into some wedges more than 2 m, indicating that fracturing is still active today. Complex fracture fillings in bedrock also have been attributed to a permafrost origin, but this too seems unlikely.

Asphalt-impregnated sediments at Rancho La Brea (Los Angeles County) and McKittrick (Kern County) in California provide a rich Quaternary insect record. Ages of various sites at Rancho La Brea range from more than 40,000 14C yr B.P. to modern. McKittrick insects studied by W. D. Pierce are not contemporaneous with the late Pleistocene vertebrate fauna, but are only about 7000 14C yr old. The major paleoecological groupings are: (1) ground dwellers, (2) aquatics. (3) scavengers, and (4) miscellaneous. Contrary to conclusions of earlier authors, most specimens represent modern species. Only two apparent terminal Pleistocene extinctions are recognized. both dung beetles (Scarabaeidae).

Pingos, or ice-cored mounds, are described for the first time from Antarctica and for the first time on ice-cored moraine. Seven pingos up to 4 m high and 12 m in diameter occur on former dering of lakes on the moraine exposes water-saturated sediments to freezing and consequent lake sediments on Flanders Moraine, Vestfold Hills, Antarctica (68°40'S 78°00'E). Lateral wandering formation of closed-system pingos. The pingos are probably only a few hundred years old. The apparent absence of pingo scars in the Southern Hemisphere may be due to lack of suitable substrates, rather than to unsuitable climatic conditions.

The pulse of large mammal extinctions at the close of the last ice age was a pronounced ecological catastrophe in the Western Hemisphere. Available paleoenvironmental, paleontological, and archeological data are largely concordant with the “overkill” hypothesis proposing that human predation was the cause of these extinctions. Climatic explanations fail to postulate specific mechanisms accounting for the event's timing, differential impact, geographic extent, and stratigraphic singularity. Lack of provisional acceptance of the overkill hypothesis, when no viable alternatives exist, may be in part because this unconventional hypothesis violates a strong sociocultural bias, the image of prehistoric man as the “noble savage”.

Pleistocene proboscidean fossils recovered from the Bering Land Bridge strengthen the hypothesis that man may have originally colonized the Americas via this route during times of lowered sea level.