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Tree macrofossils dating from the middle to end (about 1000 years, ca. 12 600-11 600 cal years BP) of the Younger Dryas chronozone were found in an organic deposit on the southwest side of the Mohawk River, near its junction with the Hudson River in Cohoes, New York, USA. The fossils included substantial wood fragments, associated plant remains, and pollen, which indicate a forest of white spruce ( Picea glauca), balsam fir ( Abies balsamea), and tamarack ( Larix laricina). The presence of white, rather than black ( P. mariana) or red ( P. rubens) spruce in the Younger Dryas was probably due to a riparian-type environment, confirmed by its location and American beaver tooth marks on some of the wood fragments. The clusters of wood radiocarbon dates indicate periodic changes in erosion and deposition at the site. One possible but very short decline (temperature reversal?) may be indicated by tree-ring growth, but in general, the ring widths of the trees and their growth responses suggest variable but slowly improving conditions over time, possibly from warming temperatures, before the end of the Younger Dryas. [ABSTRACT FROM AUTHOR]

The Acadian deformation front in the northern Appalachians of Maine and New Hampshire can now be closely located during the early Emsian (Early Devonian; 408-406 Ma). Tight correlations between paleontologically and isotopically dated rocks are possible only because of a new 408-Ma time scale tie point for the early Emsian. The deformation front lay between a belt of Lower Devonian fiysch and molasse that were deposited in an Acadian foreland basin and had not yet been folded and a belt of early Emsian plutons that intruded folded Lower Devonian rocks. This plutonic belt includes the newly dated Ore Mountain gabbro (U/Pb; 406 Ma), which hosts magmaticsulfide mineralization. Along the deformation front, a 407-Ma pluton that locally truncates Acadian folds (Katahdin) was the feeder to volcanic rocks (Traveler Rhyolite; 406-407 Ma) that are part of the foreland-basin succession involved in these same folds. The Emsian igneous rocks thus define a syncollisional magmatic province that straddled the deformation front. These findings bear on three alternative subduction geometries for the Acadian collision. [ABSTRACT FROM AUTHOR]

Determines the [sup40]Argon-[sup39]Argon geochronometry of pseudotachylytes from the North Cascade Mountains in Washington by vacuum encapsulation. [sup39]Argon loss; Textural and minerological features; Differences between total-gas age, argon-retention age and plateau age.

Examines crystal residence times using in situ uranium-lead (U-Pb) dating of zircons from the Bishop Tuff in east-central California. Maximum mean crystal residence time for zircon; Analysis of zircons from fallout and intercalated ash-flow deposits and unpolished rims; Storage of Bishop Tuff rhyolite prior to eruption.

Examines the use of optical dating of dune sand for the study of sea-level change in Massachusetts. Agreement on sea level between optical ages of barrier dune sand and evidence from salt-marsh peat sampled behind the barrier; Relevance of accurate records of relative sea-level change in modelling isostically forced crust and mantle behavior.

Analyzes the dating of single zircon grains from granite cuttings from southeastern Georgia. Age of the granite; Composition; Implications of the new data to the Suwannee terrane subcrop age province boundaries.

Presents a 40Ar/39Ar thermochronological analysis of Mesoproterozoic metamorphism in the Colorado Front Rage. Presence of staurolite, andalusite, cordierite, and garnet porphyroblasts overprinting earlier assemblages; Interpretation of muscovite and biotite ages; Observation of thermal effects for plutons, suggesting pervasive, regional crustal heating.

Examines the reliability of 10Be produced in situ in dating moraines located in Wind River Mountains, Wyoming. Dryas; Cosmogenic-nuclide surface-exposure methods of dating boulder or bedrock surfaces.

Documents the thermal history of rocks surrounding the 1.43 Ga Priest pluton in Manzano Mountain, central New Mexico, using metamorphic studies and 40Argon/39Argon dating. Proterozoic geology of the central and southern Manzano Mountains; Evidence for polymorphism preserved by rocks surrounding the Priest pluton; Regional metamorphic conditions.

Presents 40Ar/39Ar laser microprobe dates on detrital mineral grains extracted from sandstones of the Gravina belt, southeastern Alaska. Reconstruction of the geochronological characteristics of the Gravina belt source area; Age constraints for Gravina belt stratigraphy and regional tectonics; Multiple grain dating of primary volcaniclastic detritus.

Presents the results of a uranium-lead sphene dating of metamorphism in the Red Mountain pluton, Laramie Mountains, Wyoming. Boundaries of study area; Red Mountain pluton and its aureole; Sample descriptions; Strategies for interpreting uranium-lead data from low uranium materials.

Comments on the evidence presented by Anthony R. Prave (1999) regarding the age of the Proterozoic Kingston Peak Formation in Death Valley, California. Sordough Limestone Member as one of carbonate units within Kingston Peak Formation; Comparison of data from Death Valley rocks with chemostratigraphic record from other Neoproterozoic rocks; Reply of Prave.

Focuses on decisions of geologists at Washington DC to work out plans for a more accurate and complete geological timescale. Tasks that would be undertaken by an international network of laboratories; Comments of geochronologist Samuel Bowring on the project; Usefulness of uranium -- lead isotopes measurements in determining the accurate time during which the Cambrian explosion took place.

Presents news briefs related to science. United States legislation for permanent tax credit for research and development investments; Controversy over the Kennewick Man, found in the bank of Washington's Columbia River; Failure to date the remains; Claims laid by Native American tribes.

Reports that Arizona State University geographer Ronald I. Dorn is under investigation for possible scientific misconduct, as of March 19, 1998. Questions about the dating of rock varnish; Background of investigation; Interest in Dorn's methods; Dorn's research on petroglyphs in the petrified forest region of northeastern Arizona; Scholarly debate about rock varnish; Forthcoming paper in `Science.'

Reports that Earth scientist Wallace Broecker of Columbia University has settled out of court with Arizona State University (ASU) geographer Ronald Dorn who brought suit against him. Dorn's claim that Broecker defamed him in an article published in the periodical 'Science'; Rock dating technique espoused by Dorn and Broecker's appraisal of it which allegedly implied an accusation of data fabrication.

Explains that the rock-dating techniques of Arizona State University geographer Ronald I. Dorn have been called into question. Criticism of Dorn in `Science'; Dorn's rebuttal to the `Science' article; Questions about rock varnish samples taken from a Yucca Mountain site in Nevada; Dorn's method; Allegations that Dorn fabricated his results; Details of the investigation into the samples.