bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Polarity Stratigraphy of the Pleistocene Section at Portland (Victoria), Australia
Authors: MacFadden Bruce J. , Whitelaw Michael J. , McFadden Phil , Rich Thomas H. V. 
Published: December 2004

AbstractThree to seven oriented paleomagnetic samples were collected from 16 sites in the Nelson Bay and Bridgewater formations at Portland, Victoria, which contains the recently discovered Nelson Bay local fauna (L.F.). The entire section has reversed polarity. These results, along withGloborotalia truncatulinoideswithin the section, and the presence of underlying middle Pliocene-dated basalts, indicate that the Portland section, and the included Nelson Bay L.F., was deposited within the late Matuyama Chron between 1.66 and 0.73 myr ago. This represents the first well-documented pre-14C Pleistocene mammalian fauna in Australia calibrated in direct stratigraphic context with absolute dating methods. In addition, the reversed polarity for the Bridgewater Formation confirms the previous hypothesis that the depositional history of this beach-sand deposit is time-transgressive across the Brunhes-Matuyama boundary.
Chronostratigraphic Studies of Sediments in the Negev Desert, Using Amino Acid Epimerization Analysis of Land Snail Shells
Authors: Goodfriend Glenn A. 
Published: December 2004

AbstractThe chronostratigraphy of mostly Holocene sediments in the Northern Negev desert of Israel was studied through amino acid epimerization analysis (alloisoleucine/isoleucine ratio, A/I) of individual land snail shells and14C analysis of bulk samples of land snail shells contained within the sediments. Analysis of 31 deposits shows a very strong correlation between A/I and14C age. A/I analyses indicate that age mixtures occur within all colluvial and in some fluvial deposits. Consequently, radiocarbon dates of bulk samples, which give an average age, overestimate the time of deposition. Sedimentation rates were generally rapid in both fluvial and colluvial deposits. Colluviation shows a maximum in the early Holocene and decreases progressively thereafter, in accordance with the change in average rainfall. Accumulation of fluvial sediments shows a distinct mid-Holocene maximum and apparently relates to the interaction between variation in rainfall, extent of bedrock exposure, and vegetation density. Late Holocene fluvial deposition may relate to agricultural activity. The understanding of the chronology of sedimentation is dependent on an integrated approach employing amino acid epimerization analysis to study age variation within a layer and14C analyses for establishment of an absolute chronology.
Magnetic Stratigraphy and a Test for Block Rotation of Sedimentary Rocks within the San Andreas Fault Zone, Mecca Hills, Southeastern California
Authors: Chang Shih-Bin R. , Allen Clarence R. , Kirschvink Joseph L. 
Published: December 2004

AbstractA 500-m section of the Palm Spring Formation in the southern Mecca Hills, located within the San Andreas fault zone in southeastern California, has been paleomagnetically sampled to determine possible tectonic rotation in this area and to establish time-stratigraphic control. This work was partly stimulated by the fact that 80 km farther south, previous studies demonstrated 35° of postdepositional rotation in the Palm Spring Formation of the Vallecito-Fish Creek basin east of the Elsinore fault. Several lines of evidence suggest that hematite is the main magnetic carrier of the Mecca Hills samples. Large anhedral hematite grains observed in magnetic extracts and a positive fold test imply a detrital origin of the remanence. The polarity reversal patterns, together with earlier vertebrate paleontologic studies, restrict the time span for deposition of this unit to the middle-late Matuyama chron (2.0–0.75 myr ago), thus of uppermost Pliocene and early Pleistocene age. Characteristic directions of best least-squares fit for 73 samples suggest little or no overall rotation, despite the severe late Quaternary tectonic activity demonstrated by the intense deformation of these strata.
Late Holocene Sea-Level Record in a Core from the Puget Lowland, Washington
Authors: Eronen Matti , Kankainen Tuovi , Tsukada Matsuo 
Published: December 2004

AbstractDiatoms and lithological facies of an 8.45-m core collected from Shine swamp (47°52′20″N lat, 122°41′45″W long; about 2 m above the mean tide level) in the northern Puget Lowland reveal a rise in relative sea level during the past 6000 yr. A layer of fresh-water peat at a depth of 6.6-6.3 m (ca. 7000-5000 yr B.P.) indicates a low stand of the sea in early and middle Holocene time. About 5000 yr ago the rise in relative sea level resulted in accumulation of subtidal or lower intertidal clayey gyttja and gyttja which contain mainly marine and brackish-water diatoms (80–95%). By about 3500 yr B.P., the basin had shoaled to upper intertidal levels, and peat began to accumulate again while the sea continued its relative rise. During the period of this continuous peat growth, several alterations in fresh-water and marine/brackish-water diatom assemblages took place, indicating slight differences in the contemporaneous sea-level rise and vertical peat growth.
A 20th-Century Record of Climatologically Modulated Sediment Accumulation Rates in a Canadian Fjord
Authors: Smith John N. , Schafer Charles T. 
Published: December 2004

AbstractThe geochronology of a gravity core collected from an anoxic, high sedimentation rate (>2.5 cm/yr) setting near the head of the Saguenay Fjord in Quebec has been established for the period 1900–1979 to a resolution of better than 1 yr using a constant flux 210Pb model. Interannual variations of the sedimentation rate of between 28 and 50% are caused by rapid inputs of coarse silt and fine sand during spring freshet events. A significant correlation between sand percentage and sediment accumulation rate reflects the increase in stream competence during the spring freshet; the sand percentage parameter can be used in conjunction with sediment size parameters to estimate temporal variations in river discharge intensity. Between 1914 and 1979 sediment accumulation rates were about 60% higher during the spring and summer compared to fall and winter seasons. Both the magnitude of the Saguenay River spring discharge and the quantity of precipitation stored as snow decrease through the 20th century suggesting that the freshet intensity was governed largely by natural rather than anthropogenic (e.g., dam construction) factors. A direct correlation between sand flux, peak river discharge, and a snow storage parameter provides a link between sediment texture and climate. Detailed analyses of the grain-size distributions for dated core intervals offer a method for the reconstruction of a proxy record of paleodischarge for the Saguenay River spring freshets.
Age and Significance of Fossil White Spruce (Picea glauca), Tunica Hills, Louisiana-Mississippi
Authors: Givens Charles R. , Givens Florence Montgomery 
Published: December 2004

AbstractRadiocarbon dates indicate a Farmdalian through Woodfordian age for fossil white spruce (Picea glauca) in the Tunica Hills, a greater time span than previously documented. These dates, furthermore, require revision of the ages of fluvial terrace deposits in the region. Spruce-bearing Terrace 1 sediments, previously regarded as late Woodfordian to Holocene age, are of Farmdalian to late Holocene age. Terrace 2 sediments, previously assigned a Sangamonian or Farmdalian age, are of probable Altonian age. Plant fossils in Terrace 1 sediments represent two climatically and temporally distinct assemblages: a cool-temperate, Farmdalian-Woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak-hickory association; and a warm-temperate Holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the Tunica Hills. Locally, fossils of white spruce have been reworked into younger Terrace 1 sediments containing the warm-temperate plant assemblage. The transition from the cool-temperate flora to the modern warm-temperate flora in the Tunica Hills probably occurred around 12,000 yr B.P.
Changing Holocene Snail Faunas and Environments Along the Eastern Caprock Escarpment of Texas
Authors: Neck Raymond W. 
Published: December 2004

AbstractDetailed study of gastropods recovered from the Lake Theo Site, Briscoe County, Texas, has revealed a progressive decline in species diversity from early Holocene to the present. Knowledge of the microhabitats preferred by the recovered species allows a partial reconstruction of environments required to produce such communities. Since the early Holocene, the Lake Theo area has experienced a progressive loss of deciduous riparian gallery woodland habitat. Alteration in plant communities was caused by a dramatic decrease in effective precipitation. Analysis of the sequence of local extirpation of the various snail species indicates that the decrease in precipitation and increase in temperature probably were not concurrent.
Late Quaternary Ice-Surface Fluctuations of Beardmore Glacier, Transantarctic Mountains
Authors: Denton George H. , Bockheim James G. , Wilson Scott C. , Leide James E. , Andersen Björn G. 
Published: December 2004

AbstractFormer longitudinal profiles of Beardmore Glacier, an outlet through the Transantarctic Mountains, constrain polar plateau elevations near the center of Antarctica and ice-shelf grouding in the southern Ross Embayment. Three gravel drift sheets of late Quaternary age occur alongside Beardmore Glacier. Plunket drift, the youngest, is parallel to and 7–30 m above the present ice surface. The upper limit of Beardmore drift, intermediate in age, is within 35–40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth. The upper limit of Meyer drift, the oldest, is parallel to and 30–50 m above Beardmore drift. From correlation with numerically dated drifts farther north, we assign an early Holocene age to Plunket drift, a late Wisconsin age to Beardmore drift, and an age of marine isotope Stage 6 to Meyer drift. By our age model, Beardmore Glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by Beardmore and Meyer drifts. Most likely, grounded ice in the southern Ross Embayment caused such thickening of Beardmore Glacier almost to the polar plateau. A concomitant decline in precipitation is implied by ice-cap retreat on the nearby Dominion Range and is consistent with little change of upper Beardmore Glacier. Ice-shelf grounding most likely resulted from lowered sea level and/or basal melting. Lower than present precipitation was probably caused by colder air temperatures and more-distant open water. The Plunket profile records Holocene ice-surface lowering from increased surface ablation, decreased ice flow, or grounding-line recession.
Application of Tandem Accelerator Mass-Spectrometer Dating to Late Pleistocene-Holocene Sediments of the East Antarctic Continental Shelf
Authors: Domack E. W. , Jull A. J. T. , Anderson J. B. , Linick T. W. , Williams C. R. 
Published: December 2004

AbstractGlacial recession from the Antarctic continental shelf is recorded by glacial-marine diamictons, sands, and overlying siliceous oozes. In order to clarify the chronology for this sequence, use was made of the University of Arizona tandem accelerator mass-spectrometer (TAMS) for 14C dating. Small samples of benthic and planktonic foraminifera were selectively removed from diamictons, graded sands, and surface sediments which were recovered from the Wilkes Land continental shelf and slope, East Antarctica. Organic carbon was also utilized as a source for TAMS dating of the siliceous oozes and muds. Uncorrected ages varied from 14,260 ± 140 to 3230 ± 200 yr B.P. Carbon fixed by phytoplankton and foraminifera is strongly influenced by old, glacial-derived CO2. Thus, reservoir corrections of up to 5500 yr are needed for the 14C dates. Iceberg turbation reworks foraminifera so that dates from resulting deposits (diamictons) are interpreted as maximum ages. The consistency of corrected ages from the shelf, along with the sedimentologic interpretation, suggests a rather recent recession, perhaps mid-Holocene for this portion of the East Antarctic ice sheet. Further application of the TAMS method should help clarify other problems concerning the late Quaternary glacial history of Antarctica.
Geoarchaeological Evidence for Prairie-Mound Formation in the Mississippi Alluvial Valley, Southeastern Missouri
Authors: O'Brien Michael J. , Lyman R. Lee , Holland Thomas D. 
Published: December 2004

AbstractArchaeological materials in several prairie mounds in the northern Western Lowlands of southeastern Missouri indicate that mounds began forming prior to ca. 5000-3000 yr B.P. The mounds subsequently were inundated and built up to their modern configuration by aggradational and reworking processes. Human use of the mounds may have been tied to exploitation of aquatic animals residing in backwater habitats during periods of prolonged flooding. Principal features of the sampled portion of the mound field include preoccupation topographic highs, early occupation (ca. 5000-3000 yr B.P.) layers that drape the topographic highs, and later occupation (ca. 3000-950 yr B.P.) layers that drape earlier occupation layers and extend onto intermound areas.
Trends in Chesapeake Bay Sedimentation Rates during the Late Holocene
Authors: Donoghue Joseph F. 
Published: December 2004

AbstractTrends are discernible in the estimates of late Holocene rates of sedimentation and sea-level rise for the Chesapeake Bay. During most of the Holocene Epoch sedimentation rates and relative sea-level rise were equal, within the limits of measurement, at approximately 1 mm yr−1. Sedimentation rates measured over the past century, however, are nearly an order of magnitude higher, while the rate of relative sea-level rise for the Chesapeake Bay now averages 3.3 mm yr−1, as measured on long-term tide gauge records. When the acceleration in these rates occurred is uncertain, but it appears to have been confined to the past millennium, and probably to the past few centuries. The rapid sedimentation rates recorded during historic time may be a temporary disequilibrium that has resulted from a recent acceleration in the rate of relative sea-level rise.
Electron Spin Resonance (ESR) Dating of Hominid-Bearing Deposits in the Caverna delle Fate, Ligure, Italy
Authors: Falgueres Christophe , Yokoyama Yuji , Bibron Roland 
Published: December 2004

AbstractStalagmitic floors interstratified with Mousterian deposits from the Caverna delle Fate (Italy) have been dated by the electron spin resonance (ESR) method. Three samples dated fall between 60,000 and 74,000 yr and indicate the age of the Mousterian deposits. They are in good agreement with ages determined by nondestructive γ-ray spectrometry of the human remains from 231Pa/235U and 230Th/234U ratios, which are, respectively, yr. These dates are consistent with the morphological characteristics of the bones as Neanderthal remains.
Paleomagnetic Evidence for Repeated Glacial Lake Missoula Floods from Sediments of the Sanpoil River Valley, Northeastern Washington
Authors: Steele William K. 
Published: December 2004

AbstractRecent explanations of widespread rhythmically layered sediments in eastern Washington as the result of repeated great floods from glacial Lake Missoula implicitly suggest a paleomagnetic test for validity. If each conjectural flood layer is separated by years or decades, as hypothesized, a sequence of several such flood beds should record measurable secular variation in geomagnetic field direction. In the Sanpoil River valley where the rhythmite sequences are thought to have been deposited in glacial Lake Columbia, the paleomagnetic test consists of measuring remanent magnetization (RM) directions for thick, upwardly fining beds inferred to be sediments deposited by the influx of flood waters from glacial Lake Missoula into glacial Lake Columbia. Laboratory measurements of samples from three widely spaced sections along the Sanpoil River yield RM vectors with erratic inclinations, apparently affected by varying contributions of inclination error and (or) compaction shallowing, but with declinations that generally differ statistically from one flood to the next and that show the same west-to-east trend at all three locations. The rates of declination change inferred from these data are consistent with modern rates, thus providing the first geophysical evidence supporting the timing in the tens-of-floods theory.
Marine Episodes in Hudson Strait and Hudson Bay, Canada, during the Wisconsin Glaciation
Authors: Laymon Charles A. 
Published: December 2004

AbstractTwelve reworked shell fragments were recovered from five till samples collected on Nottingham Island in western Hudson Strait, Canada. Total hydrolysate amino acid ratios (D-alloisoleucine/L-isoleucine) for each fragment range from 0.043 to 0.154 and are significantly higher than ratios for radiocarbon-dated Holocene shells, which average 0.022. One shell fragment with an aIle/Ile ratio of 0.065 yielded an AMS radiocarbon age of 44,200 ± 2300 yr B.P. (AA-3254). Absolute age estimates based on the amino acid ratios are constrained by reasonable limits on the estimated effective diagenetic temperature of the fossils. On this basis, the shell fragments are correlated with oxygen isotope substages 5e and 5a and stage 3 in the preferred hypothesis. Theses results independently support hypotheses calling for at least partial deglaciation and marine incursion in Hudson Strait and Hudson Bay at these times.
Coastal Aminostratigraphy of the Last Interglaciation in Southern Australia
Authors: Murray-Wallace Colin V. , Belperio Antonio P. , Picker Kelvin , Kimber Ronald W.L. 
Published: December 2004

AbstractAmino acid racemization data for marine molluscs of the last interglaciation from southern Australia provide the basis for a predictive model for relative dating of late Quaternary sequences. Genera analyzed includeAnadarasp.,Katelysiasp.,Glycymerissp., andFulviasp. that exhibit moderate racemization rates. A genus effect on racemization is not evident in these taxa. Coefficients of variation for intershellD/Lratio variation for each deposit are generally less than 12%. The extent of racemization in molluscan fossils of the last interglaciation from temperate coastal settings in southern Australia represents an exponential function of temperature and is in general accord with data from Northern Hemisphere sites with similar contemporary mean annual temperature values. These data highlight the potential of amino acid racemization for global correlation programs. The amino acid data from southern Australia suggest, however, that a larger margin of variation may have to be accounted for in stratigraphic correlation, as indicated by the greater scatter of data around the oxygen isotope substage 5eisochron. These data have implications regarding the age-resolving power of amino acid racemization.
Chronological Separation of Interglacial Raised Beaches from Northwestern Europe Using Thermoluminescence
Authors: Balescu Sanda , Packman Susan C. , Wintle Ann G. 
Published: December 2004

AbstractThermoluminescence (TL) age estimates have been obtained on coarse-grained detrital feldspar from Eemian beach sand (substage 5e), early Weichselian dune sands (substages 5d and 5b), and pre-Eemian beach sand. The past radiation dose is obtained using the additive dose method. Even for the oldest samples, which date to 300,000 yr B.P. by other methods, the TL signal is not in saturation and can be doubled by the addition of laboratory radiation doses without saturation being achieved. This is contrasted with the behavior of polymineral, silt-sized grains from loess in the adjacent area. The TL age estimates are systematically underestimated by about 40% when compared with the expected geological ages. However, they are in correct stratigraphic order and demonstrate that stage 5 beach deposits can be distinguished from those resulting from earlier high sea levels using TL signals from potassium feldspars.
Characteristics and Origin of Rock Varnish from the Hyperarid Coastal Deserts of Northern Peru
Authors: Jones Charles E. 
Published: December 2004

AbstractThe characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern Peru, combined with laboratory experiments on associated soil materials, provide new insights into the formation of rock varnish. The Peruvian varnish consists of an Fe-rich, Mn-poor component covering up to 95% of a varnished surface and a Fe-rich, Mn-rich component found only in pits and along cracks and ridges. The alkaline soils plus the catalytic Fe oxyhydroxides that coat much of the varnish surfaces make the Peruvian situation ideal for physicochemical precipitation of Mn. However, the low Mn content of the dominant Fe-rich, Mn-poor component suggests that such precipitation is minor. This, plus the presence of abundant bacteria in the Mn-rich varnish and the recorded presence of Mn-precipitating bacteria in varnish elsewhere, suggests that bacteria are almost solely responsible for Mn-precipitation in rock varnish. A set of experiments involving Peruvian soil samples in contact with water-CO2solutions indicates that natural fogs or dews release Mn but not Fe when they come in contact with eolian materials on rock surfaces. This mechanism may efficiently provide Mn to bacteria on varnishing surfaces. The lack of Fe in solution suggests that a large but unknown proportion of Fe in varnish may be in the form of insoluble Fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish. The results of this study do not substantively change R. I. Dorn's paleoenvironmental interpretations of varnish Mn:Fe ratios, but they do suggest areas for further inquiry.
Late-Glacial to Holocene Changes in Winds, Upwelling, and Seasonal Production of the Northern California Current System
Authors: Sancetta Constance , Lyle Michell , Heusser Linda , Zahn Rainer , Bradbury J.Platt 
Published: December 2004

AbstractA core 120 km off the coast of southern Oregon was examined for changes in lithology, diatoms, and pollen over the past 30,000 yr. Primary production during the late Pleistocene was about half that of the Holocene. Evidence from diatoms and pollen indicates that summer upwelling was much weaker, implying an absence of strong northerly winds. Early Pliocene diatoms found throughout the late Pleistocene section were probably derived from diatomites east of the Cascades and provide evidence for strong easterly winds over a dry continental interior. The findings verify predictions of a climate model based on glacial maximum conditions. There is no compelling evidence for a climatic reversal corresponding to the European Younger Dryas chron. During the early Holocene (9000−7000 yr B.P.) there may have been years when winds were insufficiently strong to support upwelling, so that warm stratified waters lay closer to the coast.