Geomorphic threshold conditions have been identifed at which stream patterns change and gully initiation occurs. For both, the threshold conditions are defined by the parameter of “relative shear stress” which is a measure of the energy state of the system and is based on known values of stream slope and mean annual discharge (for patterns) or drainage area (for gullies). The probability of passing from a stream pattern to another, or from stable to gullied valley floors, is a smooth function of relative shear stress and so the thresholds separating the different states of the geomorphic systems are gradational. The singularity of landforms prevents the identification of a sharp threshold, and as a result landform sensitivity will differ within the same area and under the same conditions. Therefore, geomorphic predictions and postdictions will be uncertain, and Quaternary correlations will lack precision.

Small ice fields on the western cordillera northeast of Lima were expanded to three times their present size in the recent past, and the regional snow line was probably about 100 m lower than it is today. Outwash from the expanded glaciers formed deltas of silt in valley-bottom lakes. When the ice lobes retreated, the reduced outwash was trapped behind recessional moraines, and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools. The delta surfaces then became covered with peat, and radiocarbon dates for the base of the peat (1100 ± 70 and 430 ± 70 yr B.P. for two different deltas) indicate that the maximum ice advance was older than those dates and, thus, older than the Little Ice Age of many north-temperate regions. Much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys, which had previously been inundated by the cordilleran ice field. The cordilleran deglaciation and this expansion of local glaciers probably occurred between 12,000 and 10,000 yr ago, on the basis of slightly contradictory radiocarbon dates.

The Ruby Mountains-East Humboldt Range, one of the interior mountain groups of the Basin and Range Province, lies about midway between the Wasatch Mountains and the Sierra Nevada. After Blackwelder's description in his review of glaciation in the western mountains, Sharp mapped and named the deposits of the Lamoille and Angel Lake glaciations and correlated them with early and late Wisconsin deposits of the Great Lakes area. The refinement of relative dating (RD) methods, the availability of airphotos and modern topographic maps, and new road cuts have aided the restudy of these alpine glacial deposits and the basis for their correlation. Lamoille moraines are smooth ridges and show little detail of constructional topography. Valleys glaciated only by Lamoille ice still show the characteristics of a glaciated trough, but they have been greatly modified by weathering and erosion. Granite boulders on Lamoille moraines are pitted, and pegmatites have grotesque shapes with 30-cm-deep pits. Cuts through Lamoille end moraines (and alluvial talus cones) expose a thick soil profile with a well-developed blocky structure in a reddish-brown argillic B horizon. Subsurface granitic boulders in the B horizon of Lamoille tills show much greater weathering than do those in Angel Lake tills. In contrast, Angel Lake moraines are irregular and rugged, contain closed depressions, and have been little altered since deposition. Surfaces scoured by Angel Lake ice are fresh and unweathered. Granites of Angel Lake moraines have weathered surfaces but show little pitting; pegmatites have pits up to 10 cm deep. The thin soil profiles on Angel Lake tills and alluvial talus cones display brown colors, minor clay accumulation, and no B-horizon structure. These weathering and morphological differences suggest that the Lamoille deposits have been exposed to weathering and erosion for a period of time as much as an order of magnitude longer than the Angel Lake deposits. Thus only the Angel Lake is Wisconsinan in age, and the Lamoille drift is more reasonably correlated with the Illinoian Stage of the Great Lakes region.

Tephra layers near Glacier Peak in the North Cascade Range provide limiting dates for four periods of alpine glacier advance. Field relations suggest that late Wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from Glacier Peak about 11,250 yr B.P. Late Wisconsin deglaciation in the central North Cascades was complete prior to the Glacier Peak tephra eruptions. Glaciers again expanded in the early Holocene about 8400 – 8300 yr B.P. Soil formed in alpine meadows during an episode of mild climate in the middle Holocene prior to at least two intervals of glacier expansion: an older episode between 5100 and 3400 yr B.P., and a younger episode within the last 1000 yr.

Sea-level changes in Beringia are especially significant because they affect the migration of land plants and animals between Asia and North America, and marine plants and animals between the Pacific and Arctic oceans. Previous studies of cores from the Bering and Chukchi shelves produced sea-level curves. Evaluation of these data suggests that nine of the radiocarbon-dated estimates of sea-level position are most reliable for the time period 19,000 to 10,000 yr B.P. The trend of these nine points is proposed as the basis for a regional sea-level curve for central Beringia. Constraints on the data must be noted, however, by anyone using them.

New radiocarbon dates, carbon and oxygen isotope analyses of mollusks and marl, and palynologic analysis have clarified age relationships at the Corry kettle bog in northwestern Pennsylvania. A 4000-yr difference in radiocarbon dates between basal peat and marl top, previously interpreted as caused by the presence of an unconformity, is reinterpreted as due to “hard-water effects” from carbonate bedrock and glacial deposits. A radiocarbon date of 14,000 yr from basal marl, previously used as a minimum age for glacial deposition, is also likely too old; instead a similar age is estimated for the base of the underlying lake clay. Radiocarbon dates on marl should be used with caution and supported by isotopic and pollen analyses.

A peat bed on east-central Graham Island of the Queen Charlotte Islands occurs within a nonglacial fluvial succession that is both overlain and underlain by glacial deposits. Radiocarbon dates of 27,500 ± 400 and 45,700 ± 970 yr B.P. at the top and base of the peat, respectively, indicate that it was deposited during the mid-Wisconsin nonglacial interval. The peat is the first documented mid-Wisconsin organic deposit in northern coastal areas of British Columbia. Three local pollen zones are represented. The lowest zone (PM-1) is restricted to sandy silt directly underlying the dated peat. Very high Cyperaceae and moderate Poaceae pollen percentages characterize zone PM-1, and a variety of other herbs are common, suggesting an open landscape rather than a forested one. The middle zone (PM-2) is characterized by abundant pollen of Picea, Tsuga mertensiana, and Cyperaceae, and also contains pollen of Abies, a genus now absent from the Queen Charlotte Islands. Graham Island probably had extensive forests at this time, but abundant pollen and macrofossils of Cyperaceae and emergent aquatics such as Hippuris vulgaris, Veronica scutellata, Potentilla palustris, and Menyanthes trifoliata indicate that there also were open wetland areas. Zone PM-3 also contains abundant arboreal pollen. Large amounts of Sphagnum spores and Selaginella selaginoides megaspores indicate succession of the wetland area at the sample site to a peat bog. Paleoecological analysis of the data suggests that subalpine vegetation elements were depressed by at least 400 m, probably due to a cooler climate. Probable modern analogs in southeastern Alaska and the presence of Abies (probably A. amabilis) indicate that precipitation was higher on eastern Graham Island during the mid-Wisconsin than at present.

The faunas and floras from the Dows Local Biota provide an opportunity to compare Holocene taxa without a cultural bias. The Dows Local Biota is located in a large depression on the back side (north) of the Altamont I Moraine complex within the Des Moines Lobe. The Dows Silt Fauna/Flora ( = DSF; ca. 9380 ± 130 yr B.P.), one horizon of the Dows Local Biota, was collected for plant macrofossils, mollusks, and micromammals. DSF terrestrial gastropods are upland mesic forest dwellers although one species, Strobilops affinis, is characteristic of more xeric forests and may represent open woods. The aquatic gastropods reflect both permanent and periodic waters. DSF micromammals prefer an open, mesic, deciduous forest. The micromammal sympatry is restricted to a small area within the tension zone and deciduous forest belt of west-central Wisconsin. DSF plants are characteristic of upland forests, moist meadowlands or disturbed areas, and aquatic habitats. The DSF plant sympatry is large but restricted to the conifer-hardwood and deciduous forests along the Great Lakes-New England regions. Quantitative climatic data for the combined DSF sympatries suggest that Dows (ca. 9380 yr B.P.) was cooler than at present, and is nearly identical to that achieved by pollen analyses at the Cherokee Sewer-Lake West Okoboji sites (ca. 9000 yr B.P.) in northwest Iowa. Based on common habitat interpretations and sympatries, about 9380 yr B.P. north-central Iowa was cooler and moister than at present and was occupied by an open deciduous forest.

A thick blanket of Holocene alluvium lies over southwestern lowland Amazonia, and may possibly occur throughout much of the Amazon Basin. These deposits resulted from massive, seasonal flooding from about 11,000 to about 5000 yr B.P. that was followed by two cycles of erosion and deposition. Interpretations based on these geologic data suggest that southwestern lowland Amazonia is ecologically an “island” in a state of supersaturated disequilibrium as a result of colonization from Pleistocene refugia on its perimeter, and that habitats of highest diversity may be the most recent in origin. Conservation efforts and studies of Amazonian biogeography, soils, and paleoethnography should be reevaluated in light of the geologic data.

Mammoth remains on Santa Cruz Island, one of the four Northern Channel Islands of California, are very sparse, in marked contrast to those reported from Santa Rosa and San Miguel Islands of the same island group. A probable major reason for this scarcity is that Quaternary deposits are greatly restricted on Santa Cruz Island. It is proposed, contrary to popular opinion, that fossils found on Santa Cruz Island were derived from animals which died on the island, and were not transported there by humans. Reasons for this conclusion are that the size and geological context of the fossils are similar to those of the largest mammoth fossils of Santa Rosa Island, and that, in spite of extensive investigations by many persons, mammoth remains have not been found in middens, either on the islands or on the adjacent mainland.

Distinctive planktonic foraminiferal assemblages which characterize particular late Quaternary sapropel layers in deep basin sediments from the eastern Mediterranean Sea have been identified using cluster analysis. Three distinct clusters allow for identification and intercore correlation of the nine sapropels deposited during the last 250,000 yr. Cluster 1, representing sapropel layers S1 and S9, exhibits low abundances of Neogloboquadrina dutertrei and high abundances of Globigerinoides ruber; Cluster 2, which groups S3, S5, and S7, contains high abundances of G. ruber, N. dutertrei, and Globigerina bulloides, and Cluster 3, which includes samples from S4, S6, and S8, is marked by extremely abundant N. dutertrei and G. bulloides, and rare G. ruber. Analysis of sedimentation rates in 14 cores reveals the following approximate ages for the sapropel layers: S2 = 52,000 yr B.P.; S3 = 81,000–78,000 yr B.P.; S4 = 100,000–98,000 yr B.P.; and S5 = 125,000–116,000 yr B.P. As previously suggested, sedimentation rates on the Mediterranean Ridge were determined to be relatively constant during the last 127,000 yr. In contrast, basin sedimentation rates have fluctuated markedly from lower rates during interglacial stage 5 to higher rates during the last glacial episode. These glacial/interglacial differences are most pronounced in the northern Ionian Basin, because of increased terrigenous sediment deposition during glacial episodes. Unusually high biogenic sedimentation rates occurred in an arc south of Crete during the deposition of sapropel S5, probably due to higher productivity in this region.