Conifer wood, probably spruce (Picea sp.), of middle Wisconsinan age (29,200 ± 500 yr B.P.) was recovered from late-glacial lake sediments from Upper South Branch Pond, Maine. If the wood was derived from a local source, deglaciation of part of northern New England is suggested for this time. The occurrence also has implications for understanding the problem associated with radiocarbon dating of bulk lake sediment containing small amounts of organic matter.

The Gaap Escarpment is a dolomite cuesta demarcating the southeast margin of the Kalahari. Since Miocene-Pliocene times, thick masses of lime tufa have repeatedly accumulated at several points along this escarpment, and four regional sequences are described. These allow discrimination of six major depositional complexes, commonly characterized by basal cryoclastic breccias or coarse conglomerates that reflect frost shattering and torrential runoff, followed by sheets and lobes of tufa generated in an environment substantially wetter than today. A chronostratigraphy for the last 30,000 yr is provided by 14C dating, with direct or indirect correlations to the Vaal River sequence. The regional stratigraphy as well as faunal dating indicate an early Pleistocene age for Australopithecus africanus at Taung. Repeated episodes of protracted cold or wetter climate or both begin in terminal Miocene times, and the last Pleistocene cold-moist interval began after 35,000 yr B.P. and ended 14,000 yr B.P. Early and late Holocene times were mainly wetter, whereas the middle Holocene was drier than today. The paleoclimatic sequence differs from that of the southern and southwestern Cape or that of East Africa, but close parallels are evident throughout the lower Vaal Basin and the southern Kalahari. The tufa cycles provide a unique, 5,000,000-yr record of climatic variation in the Kalahari summer-rainfall belt that can be related to complex anomalies of the general atmospheric circulation.

Cores from five high alpine basins in the northern San Juan Mountains show several fluctuations in lithology. Typically, peats are interbedded with coarser clastic sediments or else woody peats alternate with fibrous peat. Twenty 14C dates provide radiometric control. Sediment rates averaged about 2.5 cm/100 yr but varied at the different sites between 1.19 and 50 cm/100 yr. Rates were lower during the middle of the Holocene. Basal radiocarbon dates indicate that these high (ca. 3600 m a.s.l.) northeasterly facing cirques were icefree by 9000 BP. There is some evidence in the cores for a short climatic reversal sometime between 8000 and 7000 BP. A major change occurred in the high basins very close to 5000 BP and thereafter there are several intervals of increased clastic sedimentation which may be related to Neoglacial climatic fluctuations. Analysis of a 2.15 m core near Hurricane Basin indicates significant fluctuation of pollen and macrofossils occurred during the 9000 ± year record. The Picea/Pinus ratios are used to delimit changes in the apparent elevation of the site: the ratios indicate that a short drop of “treeline” occurred about 8000 BP and then remained near present level until about ≥1800 BP when the apparent elevation of the site rose. Macrofossils indicate that spruce was present in the Hurricane Basin (and others) at specific periods and confirms the general results of the Picea/Pinus ratios. The San Juan Mountains do not possess a glacial Neoglacial record but the stratigraphy of these high cirque basins can be used to define glacial stades (cf. Jardine, 1972). The interpreted climatic response record on vegetation and sediment flux has both similarities and differences from other records in the western mountains of North America.

Tankersley and Munson (1992) reiterate that the early and, perhaps, some of the later Meadowcroft Rockshelter radiocarbon dates may be contaminated by anthropogenically derived coal or dissolved coal by-products. Their allegations are assessed in light of available data and rejected. Presently, there is no evidence whatsoever for particulate or nonparticulate contamination of any part of the Meadowcroft Rockshelter radiocarbon chronology.

Ever since the publication of the first of more than 50 internally consistent radiocarbon dates from Meadowcroft Rockshelter (36 WH297), controversy has been generated by frequent assertions that the dates older than 11,000 B.C. have suffered particulate or nonparticulate contamination. Data bearing on these assertions are assessed in the light of accelerator mass spectroscopy (AMS) dates provided by Oxford University. The weight of all data taken together suggests that this site still represents the best-dated evidence for the presence of human beings south of the glacial front in the Americas. That evidence indicates that Native Americans were present in southwestern Pennsylvania by 14,000–14,500 years ago.

All of the presently available and processed data from Meadowcroft Rockshelter indicate that the radiocarbon dates for middle and lower Stratum IIa are not discordant with either the associated fauna, flora, and artifacts or with the known geological history of the Cross Creek drainage. Consequently, it is reiterated that the earliest occupations at this locality still represent the best evidence recovered to date for the presence of pre-Clovis or pre-fluted point populations in the New World. It is further suggested that a maintenance of the "Clovis primacy syndrome" is both anachronistic and futile.

Meadowcroft Rockshelter is a deeply stratified multicomponent site in Washington County, southwestern Pennsylvania. The 11 well-defined stratigraphic units identified at the site span at least 16,000 years and perhaps 19,000 years of intermittent occupation by groups representing all of the major cultural stages/periods now recognized in northeastern North America. Throughout the extant sequence, the site served as a locus for hunting, collecting, and food-processing activities, which involved the seasonal exploitation of the immediately adjacent Cross Creek Valley and contiguous uplands. Presently, Meadowcroft Rockshelter represents one of the earliest well-dated evidences of man in the New World as well as the longest occupational sequence in the Western Hemisphere.

This date list includes those series of samples completed in this laboratory as of November, 1965. The B.P. ages are based upon A.D. 1950, and are calculated with a half-life value of 5568 yr. Errors quoted are those derived from measurements of sample, background, and modern-age calibration, and do not include any half-life error. All samples were pretreated with 3N HCl, and some, where noted, received additional pretreatment with 2% NaOH for the removal of possible humic contaminants.