bluuebunny/crossref_metadata_2025_split huggingface dataset:
Holocene Soils and Soil-Geomorphic Relations in a Semiarid Region of Southern New Mexico
Authors: Gile Leland H. 
Published: July 2006

Holocene soils of a semiarid area in southern New Mexico occur on terraces and fans in and adjacent to the mountains. The illustrative soils have formed in alluvium derived from rhyolite, monzonite, and sedimentary rocks, mainly limestone.A large arid basin occurs downslope from the mountains. In the arid-semiarid transition, the effect of a gradual increase in precipitation on soil morphology is shown by Holocene soils that sensitively reflect the precipitation. Where the parent materials contain little or no carbonate, a surficial noncalcareous zone and a reddish-brown horizon of silicate clay accumulation thicken mountainward as precipitation increases. The Bt horizon is underlain by the carbonate horizon, the upper boundary of which deepens mountainward. These orographic-depth relations and soil morphology support an interpretation that some of the clay (as well as the carbonate) is of illuvial origin. In high-carbonate parent materials, a noncalcareous zone has not developed and a reddish-brown horizon of clay accumulation has not formed.In upper horizons, organic carbon increases and color darkens towards the mountains. This causes a change in soils at the categorical level of soil order; Mollisols do not occur in the arid basin downslope, where nearly all Holocene soils are either Aridisols or Entisols. In the semiarid zone, however, most Holocene soils are Mollisols. Thick, dark A horizons have formed in many of these soils. The thickness of these horizons is attributed primarily to episodes of sedimentation during soil development. Some Holocene Aridisols also occur in the semiarid zone. Generally these are on narrow ridges, where the mollic epipedon has been truncated or did not form.In some terrains the soil-geomorphic relations are complex and Holocene soils may be above or at the same elevation as adjacent, much older soils. In such situations, when the morphological range of the various soils has been determined, soil morphology may be used to distinguish the Holocene soils and surfaces from their older analogs.
Shasta Ground Sloth (Nothrotheriops shastense Hoffstetter) at Shelter Cave, New Mexico: Environment, Diet, and Extinction
Authors: Thompson Robert S. , Van Devender Thomas R. , Martin Paul S. , Foppe Theresa , Long Austin 
Published: July 2006

AbstractSeven coprolites of the extinct Shasta ground sloth (Nothrotheriops shastense) were recently discovered in the Los Angeles County Museum collection from Shelter Cave, New Mexico. Three dung balls provided radiocarbon ages of 11,330, 12,330 and 12,430 yr B.P. Packrat (Neotoma) middens disclose a xeric juniper woodland at Shelter Cave during the sloth's occupation. Plant cuticles from the dung indicate that the ground sloth had a diet dominated by mormon tea (Ephedra) and other xerophytic shrubs. Pollen spectra from the coprolites have high representations of anemophilous plants and low representations of the dietary items shown in the cuticle analysis.Fifteen radiocarbon dates of sloth dung obtained since 1974 strengthen the hypothesis that sloth extinction occurred about 11,000 yr B.P. Paleoenvironmental studies indicate that ground sloths lived in juniper woodlands and montane conifer communities. Nothrotheriops commonly dined on shrubs that are still present in these habitats. It is difficult to explain the demise of the Shasta ground sloth by climatic change or dietary stress. Human predation remains as a possible explanation; ground sloth extinction appears to coincide with the time of Clovis mammoth hunters.
Chemistry and Mineralogy of Some Plio-Pleistocene Tuffs from the Shungura Formation, Southwest Ethiopia
Authors: Martz A. M. , Brown F. H. 
Published: July 2006

AbstractThe Shungura Formation of southwestern Ethiopia has yielded many tens of thousands of vertebrate fossils including hominids and microvertebrates, and in addition has also yielded fossil wood, pollen, and invertebrates. Widespread tuffs have made subdivision and detailed mapping of the formation possible, have provided material for potassium-argon dating, and have allowed direct lithostratigraphic correlation with the Koobi Fora Formation in northern Kenya. The basis for correlation between the two formations is the distinctive chemistry of the tuffs, but systematic chemical variation within some tuffs invalidates some statistical correlation techniques. Here chemical analysis of glass separates and minerals from tuffs of the Shungura and Usno Formations are presented which may allow further ties to be established when data become available on other tuffs of the Koobi Fora Formation. The tuffs consist primarily of glass, but also contain phenocrysts of anorthoclase, hedenbergitic pyroxene, sodic amphibole, ilmenite, titanomagnetite, chevkinite, quartz, zircon, and rarely orthopyroxene and plagioclase. The glasses show evidence of alkali loss during hydration, and are not now peralkaline, although it is likely that they were initially. The source volcanoes were most likely situated within the Ethiopian rift valley, or on its margins.
Late Quaternary Floodplain Sedimentation along the Pomme de Terre River, Southern Missouri
Authors: Brakenridge G. Robert 
Published: July 2006

AbstractNew cross sections and dates from along the Pomme de Terre River clarify the complex local history of valley development and floodplain sedimentation. The observed history begins with a series of ancient bedrock strath terraces that record past bedrock valley positions at 15.5 to more than 58 m above the modern bedrock floor. Each strath is capped by 1–2 m of channel gravel and sand permeated by red clay. Sometime previous to ca. 140,000 yr B.P., a much lower bedrock valley only about 5–6 m above the modern level was excavated. By 140,000 yr B.P., accumulation of red and gray mottled silty clay had commenced, and had reached to 8.5 m above the modern floodplain before 48,900 ± 900 14C yr B.P. Sometime between ca. 49,000 and 45,000 14C yr B.P., erosion caused abandonment of an oxbow meander, and lowered the bedrock valley to about its present depth. Younger yellowish-red and gray mottled silty clay alluvium then began accumulating. This mid-Wisconsinan fill reached to 2.5 m above the modern floodplain sometime before 31,800 ± 1340 14C yr B.P., at which time another erosional phase was in progress. A late Wisconsinan olive clay accumulated between 27,480 ± 1950 and ca. 23,000 14C yr B.P., followed by approximate stability until 13,550 ± 400 14C yr B.P. After stability, an erosional episode began, but by 10,200 ± 330 14C yr B.P., deposition of a distinctive brown clayey silt was underway. This early Holocene fill reached to about the same level as the mid-Wisconsinan fill by 8100 ± 140 14C yr B.P. Erosion occurred between this date and 7490 ± 170 14C yr B.P., but the former floodplain level was rapidly reattained, and was apparently stable until ca. 5000 14C yr B.P. Finally, erosional unconformities and 17 dates from the brown clayey silt, and from younger grayish-brown silty sand underlying the modern floodplain, record subsequent episodes of floodplain erosion at ca. 5000, 2900, 1500 and 350 14C yr B.P. The timing of Pomme de Terre floodplain sedimentary regimes, characterized by net aggradation, erosion, or stability, may have been controlled by climate. In particular, both periods of stability appear to have been coeval to times of strongly zonal upper atmospheric circulation. Intensified zonal circulation would have resulted in less frequent large floods and an increased dominance by floods of small to moderate size. In contrast, there are no obvious parallels to be drawn between this local alluvial history and sea level or glacial outwash induced baselevel changes.
Brunhes-Matuyama Magnetic Reversal Dated at 790,000 yr B.P. by Marine-Astronomical Correlations
Authors: Johnson R. G. 
Published: July 2006

AbstractThe presence of the Brunhes-Matuyama magnetic reversal in deep-sea core sediments makes possible an alternative to the usual K/Ar radioistope method of dating the reversal as found in rocks. The alternative method uses correlations of Northern Hemisphere summer insolation with oxygen-isotope ratios from tropical cores. The latitude-dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale. The insolation variations strongly influence glacial-ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments. The summer half-year insolation variations are identified with corresponding isotope-ratio changes in cores from the present through glacial Stage 20. Misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of V28-238 and V28-239, the principal cores studied, and by comparisons with other cores. The top section (Stages 1 to 10) of V28-238 is uniformly deposited, and for this section an isotope-ratio time scale is chosen that agrees with the thorium-uranium date for the high sea stand of the last interglacial extreme. Over this interval, major glacial extremes (strong isotope-ratio minima) coincide consistently with major insolation minima at times of low orbital eccentricity. In addition interstadials are directly associated with precessional insolation peaks, and the envelope of isotope-ratio peaks resembles the envelope of precessionally dominated insolation peaks. The assumption that the glacial extremes depended similarly on insolation minima during Stages 10 to 20 permits minor age shifts of strong isotope-ratio minima in the two cores (relative to ages based on uniform overal deposition) to match the ages of low-eccentricity insolation minima. The age shifts reflect residual nonuniformities of deposition. The validity of this matching procedure is supported by a resulting consistent identification of principal isotope-ratio peaks with high- and low-latitude coincident insolation maxima. The Brunhes-Matuyama reversal is found intinterglacial Stage 19, and is dated on the astronomical time scale at 790,000 ± 5000 yr B.P.
Seismic Reflection Study of Recessional Moraines beneath Lake Superior and Their Relationship to Regional Deglaciation
Authors: Landmesser C. W. , Johnson T. C. , Wold R. J. 
Published: July 2006

AbstractApproximately 8000 km of continuous seismic reflection profiles throughout Lake Superior were examined for evidence of recessional moraines and other ice-margin deposits associated with the retreat of late Wisconsin ice. These features are correlated with the record of glacial-lake evolution in western Lake Superior. An offlapping sequence of glacial and glacial-lacustrine sediments overlying bedrock is recognized in west-central Lake Superior that is progressively younger to the northeast. The sequence underlies more recent glaical-lacustrine and postglacial sediments. Four facies are recognized on the basis of geomorphologic and acoustic properties and are interpreted to represent a southwest-to-northeast assemblage of: proglacial stratified drift (facies A), drift in major end moraines (facies B), till deposited as glacial retreat resumed, or possibly late-stage ablation till (facies C), and basal till (facies D). The prominent moraines of facies B are unusually thick and are believed to mark the ice-margin shorelines of successive major proglacial lakes that formerly occupied parts of western Lake Superior. The moraines are tentatively correlated with Glacial Lake Duluth (unit 1), Glacial Lake Washburn (unit 2), and Glacial Lake Beaver Bay (unit 3), the most prominent of lakes drained via the progressively lower outlets via the Moose Lake/ Brule-St. Croix Rivers, the Huron Mountains, and the Au Train-Whitefish regions, respectively.
Level of Lake Lahontan during Deposition of the Trego Hot Springs Tephra about 23,400 years ago
Authors: Davis Jonathan O. 
Published: July 2006

AbstractThe Trego Hot Springs tephra bed is a silicic tephra about 23,400 yr old, found at several localities in pluvial lake sediments in northern Nevada, southern Oregon, and northeastern California. It has been characterized petrographically, by the major and minor element chemistry of its glass, and by its stratigraphic position with respect to other tephra layers. At a newly described locality on Squaw Creek, northwest of Gerlach, Nevada, at the north end of the Smoke Creek Desert, Trego Hot Springs tephra has been found in sediments of the Sehoo and Indian Lakes formations. The depositional environments of these sediments show that when the tephra fell, pluvial Lake Lahontan stood between 1256 and 1260 m, and that immediately thereafter the lake rose to at least 1275 m. These data corroborate earlier findings by Benson (Quaternary Research9, 300–318) from radiometric dating of calcareous tufa. However, the Lake Lahontan area has been affected by isostatic subsidence and rebound in response to changing water loads, so that caution is required in the use of lakeshore elevations in correlation.
Lake-Level Variation in the Lahontan Basin for the Past 50,000 Years
Authors: Benson L. V. , Thompson R. S. 
Published: July 2006

AbstractSelected radiocarbon data on surficial materials from the Lahontan basin, Nevada and California, provide a chronology of lake-level variation for the past 50,000 yr. A moderate-sized lake connected three western Lahontan subbasins (the Smoke Creek-Black Rock Desert subbasin, the Pyramid Lake subbasin, and the Winnemucca Dry Lake subbasin) from about 45,000 to 16,500 yr B.P. Between 50,000 and 45,000 yr B.P., Walker Lake rose to its sill level in Adrian Valley and spilled to the Carson Desert subbasin. By 20,000 yr B.P., lake level in the western Lahontan subbasins had risen to about 1265 m above sea level, where it remained for 3500 yr. By 16,000 yr B.P., lake level in the western Lahontan subbasins had fallen to 1240 m. This recession appears synchronous with a desiccation of Walker Lake; however, whether the Walker Lake desiccation resulted from climate change or from diversion of the Walker River is not known. From about 15,000 to 13,500 yr B.P., lake level rapidly rose, so that Lake Lahontan was a single body of water by 14,000 yr B.P. The lake appears to have reached a maximum highstand altitude of 1330 m by 13,500 yr B.P., a condition that persisted until about 12,500 yr B.P., at which time lake level fell ≧100 m. No data exist that indicate the level of lakes in the various subbasins between 12,000 and 10,000 yr B.P. During the Holocene, the Lahontan basin was the site of shallow lakes, with many subbasins being the site of one or more periods of desiccation. The shape of the lake-level curve for the three western subbasins indicates that past changes in the hydrologic balance (and hence climate) of the Lahontan basin were large in magnitude and took place in a rapid step-like manner. The rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream, as it was forced north or south by the changing size and shape of the continental ice sheet.
Radiocarbon Dating and Paleoclimatic Significance of Subfossil Limicolaria in Northwestern Sudan
Authors: Haynes C. Vance , Mead Albert R. 
Published: July 2006

AbstractThe discovery, identification, and radiocarbon dating of the large achatinid land snail Limicolaria kambeul chudeaui at six places in northwestern Sudan, north of the 100-mm isohyet, provide convincing evidence that at least 300 mm annual rainfall existed there 6000 yr ago. Since then the rainfall north of ca. 20°N lat in the eastern Sahara has certainly been <300 mm and probably <200 mm. Accelerator mass spectrometry has allowed the organic fraction, presumably conchiolin, to be accurately radiocarbon dated whereas carbonate fractions are ca. 600 yr too old. Comparative studies show the subfossil form, L. k. chudeaui, to be the most primitive in its species complex and to occupy a narrow east-west belt across Africa north of 15°N and west of 35°E. The northern limit of living forms lies within the southern part of the Sahelian zone in forest or forest-savanna. They cannot live in open grassland. Therefore, the distribution of L. k. chudeaui marks the former northern position of this zone during the middle Holocene, indicating a latitudinal shift of at least 5° (500 km).
Late Quaternary Climatic Change in France Estimated from Multivariate Pollen Time Series
Authors: Guiot Joël 
Published: July 2006

AbstractIn regions like southern France, where usual analytical techniques are unsatisfactory due to the heavy influence of human activity and the existence of a complex climate, the quantitative reconstruction of climate from pollen is particularly difficult. That is why an original method has been performed. The first step of the method, based on best analogs estimation and multiple regression, is to calculate a relationship between climate (monthly temperature and precipitation) and modern pollen spectra for data from 182 sites. The result is called the “analog climate.” The second step of the method, an original combination of canonical correlation and principal components analyses, extracts the common information from several fossil pollen sequences to produce a so-called “paleobioclimate.” This step removes the effects of local differences in the vegetation among nearby sites and also reduces the effects of human disturbance. In the third step, the signals obtained from the first two steps are merged, by Kalman filter, into a final reconstruction where the noise is reduced by around 37%. The results, presented with a 95% confidence level, suggest that the Pleni-Würm was 7° to 13°C colder than present and had 20 to 60% less precipitation than today (this large confidence takes into account the climatic diversity of the region). At 13,000 yr B.P., the climate reached the modern level of precipitation but the temperature was just less than present. The subsequent decrease of precipitation is less important than that of temperature. This fact may explain the advance of alpine glaciers during the Younger Dryas. Preboreal warming was abrupt (3° to 4°C per 500 yr) and precipitation increased more slowly.
Polar Perspective of Late-Quaternary Climates in the Southern Hemisphere
Authors: Heusser Calvin J. 
Published: July 2006

AbstractLate-Quaternary paleoecological and glacial evidence from the higher latitudes of the Southern Hemisphere implies overall uniformity of large-scale glacial and interglacial climatic fluctuations for the past 40,000 yr. Climate of the last glacial maximum, variously dated between 30,000 and 11,000 yr B.P., was relatively cold and dry compared with the warmer, more humid climate of the Holocene and the interstade preceding the last glacial maximum. Conditions were apparently coldest during millennia centered around 20,000 yr B.P. and warmest in the early Holocene. Recorded small-scale fluctuations, frequently variable for any given time interval, are less consistent. A cold late-glacial episode, estimated as occurring between ca. 13,000 and 11,000 yr B.P. in Antarctica, possibly was coeval with the Younger Dryas Stade in northwestern Europe and may be correlative with a climatic episode in southern South America and perhaps in New Zealand and South Georgia; however, there is no evidence for the event in Tasmania. General atmospheric circulation models for the polar latitudes at the time of the last glacial maximum show an intensification of the southern westerlies, apparently a result of the expansion of ice cover in Antarctica and of sea ice in the Southern Ocean.
Holocene Alluvial Fills in the South Loup Valley, Nebraska
Authors: May David W. 
Published: July 2006

AbstractFour Holocene alluvial fills are present in Nebraska's South Loup River valley. Fill IV, the oldest and thickest, was deposited between 10,200 and 4800 14C yr B.P.; Fill III has an age of about 3000 14C yr B.P.; Fill II is younger than 2100 and older than 900 14C yr B.P.; and Fill I is younger than 900 14C yr B.P. Regional contemporaneity of valley alluviation in the eastcentral Great Plains suggests that climate has controlled long-term sediment storage in the South Loup River valley.
Does Altonian Drift Exist in Pennsylvania and New Jersey?
Authors: Ridge John C. , Braun Duane D. , Evenson Edward B. 
Published: July 2006

AbstractFrom New Jersey to southwestern New York, Altonian colluvium and fluvial gravel have been recognized beneath Woodfordian drift, but the existence of Altonian till near or beyond the Woodfordian border has not been demonstrated. Reworking of weathered materials by Woodfordian ice has produced some drift with an “Altonian” appearance. Soil criteria, applied without regard for parent material differences, have been incorrectly used to infer an Altonian age for Illinoian deposits that have a redbed provenance. The currently mapped distribution of Altonian till and the occurrence of undisturbed Illinoian deposits within areas of inferred Altonian ice cover are incompatible with the behavior of ice sheets.
Pleistocene Stratigraphy of the Boston Harbor Drumlins, Massachusetts
Authors: Newman William A. , Berg Richard C. , Rosen Peter S. , Glass Herbert D. 
Published: July 2006

AbstractEvidence from the Boston Harbor drumlins indicates that two superposed tills were deposited during glacier advances which were separated by a long nonglacial interval. At Long and Peddocks Islands, argillans and truncated clay-filled fractures, along with discontinuities in clay-mineral composition, define the till contacts. Physical indicators separating the tills are not apparent at other exposures, where till boundaries were defined solely by discontinuities in clay-mineral composition. The weathering profile in the upper part of the lower till indicates extensive weathering under a climate similar to that of today, and probably similar to that of the Sangamon Interglaciation. The depth of the weathering profile, the sequence of clay-mineral alteration products, and the presence of pedogenic features in the upper part of the lower till are comparable to Sangamonian weathering profiles in the midwestern United States, implying that the lower till is Illinoian or older.
Palynological Evidence for Increased Aridity on the Central Chilean Coast during the Holocene
Authors: Villagrán Carolina , Varela Juan 
Published: July 2006

AbstractThe late Quaternary vegetation of the semiarid coast of central Chile is inferred from the palynological analysis of profiles from Quereo (31°55′S) and Quintero (32°47′S). Prior to 11,400 yr B.P., wet conditions are suggested by the abundance of pollen indicators of swamp and aquatic taxa, such as Cyperaceae and Myriophyllum, and by the presence of traces of arboreal pollen. Since ca. 10,000 yr B.P., a trend toward increasingly drier conditions is implied by the almost complete absence of arboreal and aquatic taxa, and a general decrease in the diversity of the semiarid shrubland indicators. From 3000 yr B.P. onward, the pollen records show the reappearance of swamp and aquatic taxa, presumably associated with wetter conditions, which led to recolonization by forest taxa at 1720 yr B.P. in Quintero. The drier climate detected along the semiarid coast of central Chile during most of the Holocene extended inland to the Andean foot-hills, within the present mediterranean-type climate zone of Chile, and also affected the distribution of the winter-deciduous Nothofagus forests and the northern boundary of the temperate rain forests.