bluuebunny/crossref_metadata_2025_split huggingface dataset:
Macrofossil Analysis of wood rat (Neotoma) Middens as a Key to the Quaternary Vegetational History of Arid America
Authors: Wells Philip V. 
Published: December 2004

Wood rat (Neotoma) deposits preserved in dry rock shelters have radiocarbon ages extending from close to the present to >40,000 BP, thus providing elaborate samples of changing vegetation during the climatic shifts of the late Pleistocene and Holocene. The established record extends geographically from Oregon and Wyoming (at 45°N) south to Baja California, Sonora, and to Tehuacan (at 18°N) in southern Mexico. Several hundred ancient middens have been uncovered, and over 130 have been radiocarbon-dated.There are about 20 extant species ofNeotomawith a combined range extending from the Yukon and New England to Nicaragua and Florida. Hence, a wider application for the method seems likely, wherever dry caves favor preservation. The acquisitive rats accumulate an incredibly detailed inventory of the local flora and fauna within a small home range, measured at about 100 m or less in radius. The biomass spectrum of a modern wood rat deposit was compared with associated pollen spectra and source vegetation. The most dominant arborescent species, as determined by a quantitative study of the local vegetation, were proportionately represented in the midden, but not in the pollen rain. Less dominant species were variable in proportionality.A novel approach to the comparative ecological physiology of long-dead plants has been demonstrated with macrofossils from ancient wood rat deposits. The ratio of the stable isotopes of carbon (13C/12C) is more altered from the atmospheric proportion during CO2fixation by C3plants than it is by the different (PEP) carboxylating enzyme of heliophile or xerophytic, C4or CAM plants. Mass spectrometry of the carbon of macrofossils enables the distinction to be made in the past.The desiccated, allelochemic urine, or amberat, indurates and preserves the middens by cementing the loose debris of macrofossils into a tough, coherent mass of surprising strength and rigidity, that adheres tenaciously to rock surfaces. Water softens the most indurated middens by dissolving the crystallized urine, causing them to dislodge and to fall apart; it also removes the osmotic and allelochemic deterrent to decay by fungi, or to consumption by termites, crickets, or other decomposing herbivores. A secure position in a dry rock shelter is therefore essential to preservation of the macrofossils for time periods on the order of 104years. Attrition with time is seen in the frequency distribution of radiocarbon dates obtained on 132Neotomamiddens. The distribution is skewed toward the end of the Wisconsin glacial and the Holocene, and there is a decline in frequency with age. Cave erosion, including destructive rockfalls and new crevices that admit seepage and cause deterioration and dislodgement of the middens, is probably the main factor in the progressive attrition with increasing age.
Recent Paleolimnology of Three Lakes in Northwestern Minnesota
Authors: Birks Hilary H. , Whiteside M.C. , Stark Donna M. , Bright R.C. 
Published: December 2004

A paleolimnological study was undertaken to investigate changes in three Minnesota lakes over the last 100 years and to demonstrate the stratigraphic effects of cultural eutrophication in two of them. The study combined the analysis of the lake sediment from short cores with stratigraphic analyses of pollen, plant macrofossils, mollusks, diatoms and certain other algae, chydorid Cladocera, and Daphnia ephippia.The rise of Ambrosia type pollen (ragweed) marks the onset of interference with the landscape by European man, which can be closely dated. Calculations of sedimentation rates from this base gave reasonable correlations of other stratigraphic events with historical events.Elk Lake is considered “unpolluted” today and was chosen as a control. Man's effects are limited to logging some of the surrounding forest and to the construction of a dam. Small changes in the lake's fauna and flora are demonstrated, showing the sensitivity of the lake to changes in its catchment area.Lake Sallie and St. Clair Lake, in the same watershed as the city of Detroit Lakes, have been affected not only by logging but also by addition of nutrients from agricultural runoff and sewage effluent. Considerable responses by the lake organisms are apparent. In Lake Sallie the changes were gradual, but in St. Clair Lake they were very abrupt because the lake was partially drained at the same time and the water volume was thereby reduced.The merits of such an integrated study, the types of information gained from the analyses of the various fossils, and the wider application of the results are discussed.
Late Pleistocene Piñon Pines in the Chihuahuan Desert
Authors: Lanner Ronald M. , Van Devender Thomas R. 
Published: December 2004

AbstractExamination of late Pleistocene packrat middens from the northern and central Chihuahuan Desert disclosed macrofossils of Colorado piñon (Pinus edulis) and Texas piñon (P. remota). Radiocarbon dating indicates that Texas piñon was widespread in Trans-Pecos Texas and northeastern Mexico between 30,000 and 11,000 yr B.P. Today it is found in small refugia east of its former range. In the late Pleistocene Colorado piñon occurred at lower elevations on the northern edge of the Chihuahuan Desert. Both species occurred in the Hueco Mountains, near El Paso, Texas. No clear evidence was found of the presence of Mexican piñon (P. cembroides), though today it is abundant in the Davis and Chisos Mountains. A paleoclimate is postulated that had the following characteristics: increased winter precipitation from Pacific frontal sources, reduced summer temperatures and precipitation, and milder winter temperatures due to a reduced frequency of Arctic airmass incursion. Winter precipitation appears to have decreased from north to south, while winter temperatures, and, possibly, summer precipitation, increased from north to south. During the late Pleistocene, the northern Chihuahuan Desert was dominated by woodlands of piñon pines, junipers, and oaks. The desert-scrub communities that characterize the area today are a Holocene phenomenon.
Late Quaternary Evolution of Coastal Sand Barriers, Port Stephens-Myall Lakes Area, Central New South Wales, Australia
Authors: Thom B.G. , Bowman G.M. , Roy P.S. 
Published: December 2004

AbstractThe geomorphic and stratigraphic history of six coastal embayments has been studied in the vicinity of Newcastle, New South Wales (N.S.W.), Australia, in order to determine modes of deposition, and the degree to which marine and estuarine deposits can be correlated and dated. Each embayment possesses its own distinctive suite of landforms ranging from those dominated by coastal dunes to those in which beach ridges occur. In four of the bays dual sand barriers, comprising an Inner Barrier and an Outer Barrier, provide the framework for correlation between embayments. Six stages are recognized in the deposition of late Quaternary sediments in this area: (i) Pre-Last Interglacial, involving accumulation of separate composite units consisting of estuarine clays and transgressive dune complexes; (ii) Last Interglacial stage during which Inner Barriers were formed; (iii) Last Glacial reworking of barrier and dune sands by westerly winds; (iv) Postglacial Marine Transgression during which the Outer Barriers were initiated; (v) Mid-Holocene stage following cessation of sea-level rise ca. 6000–6500 yr B.P. on this coast, and involving progradation of Outer Barriers in some embayments; and (vi) Late Holocene episodic eolian reworking of dune complexes and Outer Barriers. The relatively high wave and wind energy as well as the tectonic setting of the central N.S.W. coast results in somewhat different geomorphic histories from barrier-island coasts in North America and Europe.
Historical Ecology in Beringia: The South Land Bridge Coast at St. Paul Island
Authors: Colinvaux Paul 
Published: December 2004

AbstractA 14-m core of lake sediments from St. Paul Island yields a long environmental history of the south coast of the Bering land bridge. Tritium assay demonstrates that sands in the bottom 8 m of deposit are injected with modern water, suggesting that a radiocarbon anomaly is the result of modern carbon introduced in groundwater. The remaining radiocarbon chronology, coupled with a time-stratigraphic pollen-zone boundary suggests that the record penetrates to the mid-Wisconsin interstadial. Pollen percentage data,Piceapollen influx, and pollen species lists allow reconstruction of the land bridge vegetation, which was tundra, without shrubs or trees, with bare ground, and comparable to Bering land bridge tundras found further north. There was no coastal mild or wet strip. Plant associations comparable to those of the modern Aleutians or Pribilofs probably did not exist along the land bridge coast and the region was probably not suitable for breeding by fur seals and other marine mammals. A cold, dry, continental air-mass system reached to the coast itself. The south land bridge coast did not offer an environment to aboriginal human populations that was significantly milder than that of the land bridge plains to the north. At about 11,000 yr B.P. the Wisconsin dry climate was replaced by a regimen comparable to that at the modern tree line of the interior, and this climate in turn was replaced with the modern system at about 9500 yr B.P. Climatic change was independent of fluctuating sea level.
Late Quaternary History of Lake Manitoba, Canada
Authors: Teller James T. , Last William M. 
Published: December 2004

AbstractThe postglacial history of Lake Manitoba has been deduced from a study of the changes in physical, mineralogical, and chemical variables in sediment cores collected from the lake. Six lithostratigraphic units are recognized in the South Basin of the lake. Weakly developed pedogenic zones, reflecting dry or extremely low water conditions in the basin, separate five of these six units. The initial phase of lacustrine sedimentation in the Lake Manitoba basin began shortly after 12,000 yr B.P. as water was impounded in front of the receding glacier to form Lake Agassiz. By 11,000 yr ago, continued retreat of the ice sheet opened lower outlets to the east and much of Lake Agassiz drained, including the Lake Manitoba basin. Water levels again rose at 9900 yr B.P., but by about 9200 yr B.P. the South Basin was again dry. For the next 4700 yr there was an alternation of wet and dry conditions in the basin in response to the interaction of a warmer and drier climate and differential crustal rebound of the basin. About 4500 yr ago a new phase of Lake Manitoba sedimentation was initiated when the Assiniboine River began to discharge into the South Basin. The Assiniboine River was diverted out of the Lake Manitoba watershed about 2200 yr ago. Erosion and redistribution of the sandy deltaic sediments deposited by the Assiniboine River has created the barrier beach that now separates the extensive marsh to the south of the lake from the main lake.
Evidence of Multiple Late-Wisconsin Floods from Glacial Lake Missoula in Badger Coulee, Washington
Authors: Bunker Russell C. 
Published: December 2004

AbstractCatastrophic floods from glacial Lake Missoula entered the Pasco Basin in south-central Washington and backflooded its marginal valleys. Badger Coulee, one such valley, contains beds of fine-grained slackwater sediment deposited by these floods. The slackwater sediment contains two ash layers of the Mount St. Helens set S tephra, about 13,000 yr old. The ash was deposited on a ground surface developed atop slackwater sediment deposited during preash flooding. Evidence of the former ground surface includes the reworked ash, inferred trace fossils, stream and debris-flow deposits, slopewash and/or eolian sediment, and colluvium at the ash horizon. These features and the ash were buried by slackwater sediment deposited during postash flooding. Nonflood, subaerial deposits are not present atop other beds. Instead, beds commonly are reversely graded across “contacts,” suggesting that multiple beds were continuously deposited. The exposed beds thus record at least two late-Wisconsin floods, one preash, the other postash. The pre- and postash floods may be correlative with earlier-reported floods thought to have occurred 17,500-14,000 and 14,000–13,000 yr B.P., respectively.
A Climate-Related Oxidizing Event in Deep-Sea Sediment from the Bering Sea
Authors: Gardner James V. , Dean Walter E. , Klise David H. , Baldauf Jack G. 
Published: December 2004

AbstractMany cores from the deep basins of the Bering Sea have a thin oxidized zone within otherwise reduced sediment. This oxidized zone began to form about 6000 yr ago and represents an interval of about 3200 yr. Mineralogically, the oxidized and reduced sediments are similar, but chemically they differ. Concentrations of Fe and C are lower, and concentrations of Mn, Ba, Co, Mo, and Ni are higher in the oxidized than in the reduced sediment. Mn is enriched about 10-fold in the oxidized zone relative to its concentration in the reduced sediment, Mo about threefold, and Ba, Co, and Ni about twofold. These data suggest that the oxidized zone developed diagenetically as the result of the balance between the flux of organic matter and the available dissolved oxygen in bottom and interstitial waters.We propose that the Bering Sea was substantially ice covered when global glacial conditions prevailed. during the transition to global interglacial conditions, seasonal meltwater from thawing sea ice formed a lens of fresh water that decreased organic productivity. During the winter seasons, however, sea ice reformed and caused downwelling of dense, oxygen-rich waters to recharge bottom waters. The combination of lower organic productivity and more oxygen-rich bottom water allowed oxidized sediment to accumulate. Once full interglacial conditions were established, the volume of sea ice produced was insufficient to affect either productivity or the supply of dissolved oxygen and so bottom conditions again became reducing.Similar events probably occurred during the onset of global glacial conditions, and similar oxidized layers probably formed at these times. Such oxidized zones are highly unstable, however, in a reducing environment and, once buried beyond the influence of bacterial and infaunal activities, are depleted of their available oxygen and converted to reduced sediment.
Stratigraphy, Pollen Analysis, and Paleoclimatic Interpretation of Pulbeena Swamp, Northwestern Tasmania
Authors: Colhoun E. A. , van de Geer G. , Mook W. G. 
Published: December 2004

AbstractSedimentary, palynologic, and14C analysis of 480 cm of freshwater marl and swamp-peat deposits, formed under the influence of fluctuating artesian springs, provides a paleoenvironmental and paleoclimatic record of approximately 65,000 yr for northwestern Tasmania.The Holocene (Pollen Zone 1, 11,000-0 yr B.P.) climate was warm and moist, and forest vegetation was dominant throughout the area. During the later part of the last glacial stage (Pollen Zone 2, 35,000–11,000 yr B.P.) the climate was generally drier, and grassy open environments were widespread. The driest part of this period occurred between 25,000 to 11,000 yr B.P., when temperatures in western Tasmania were markedly reduced during the last major phase of glaciation. Prior to 35,000 yr B.P. (Pollen Zones 3–9) a long “interstadial complex” dating to the middle of the last glacial stage is recognized. During this period the climate was generally moist, and forest and scrub communities were more important than during the later part of the last glacial stage, except during Pollen Zone 5 when high Gramineae plus Compositae values suggest drier conditions. High Gramineae and Compositae values also occur in Pollen Zone 10 at the base of the diagram. They suggest that a phase of drier and cooler climatic conditions occurred during the early part of the last glacial stage.
A Late Quaternary Pollen Record from the Transvaal Bushveld, South Africa
Authors: Scott Louis 
Published: December 2004

AbstractPollen spectra from cores of organic spring deposits from the Transvaal provide evidence for the climatic evolution of the province during the last 35,000 yr B.P. or more. The past climatic phases are derived from palynological reconstructions of past vegetation types by comparison of fossil pollen data with modern surface pollen spectra from various localities. Evidence is provided for an early moist, cool phase with relatively mesic bushveld and expanded montane forest in the central Transvaal, followed by a drier period with drier bushveld which probably lasted until approximately 25,000 yr B.P. During the next phase, which at the latest ended about 11,000 yr B.P., the temperatures were probably 5°–6°C cooler than at present. At that time bushveld vegetation in the central Transvaal was replaced by open grassland with macchia elements. Climatic amelioration came and semiarid savanna returned to the plains, at first gradually and then developing into a warm Kalahari thornveld-type vegetation. After 6000 yr B.P. it apparently became slightly wetter and a more broad-leafed bushveld developed. About 4000 yr B.P. it again became cooler and slightly wetter and the bushveld vegetation on the central and northern plains was comparable to present open upland types. After 2000 yr B.P. conditions gradually became warner until about 1000 yr B.P., when the modern climate of the central Transvaal bushveld originated.
Palynology of Cushion Bogs of the Cordillera Pelada, Province of Valdivia, Chile
Authors: Heusser Calvin J. 
Published: December 2004

AbstractFossil pollen identified in the earliest sediments of three cushion bogs in the Cordillera Pelada (40°10′S, 73°30′W) dated 10,425 14C yr B.P. includes the subantarctic species Dacrydium fonckii, Tetroncium magellanicum, Astelia pumila, Gaimardia australis, Donatia fascicularis, and Drosera uniflora. All grow today in the Cordillera Pelada and range poleward to the southernmost Province of Magallanes; one species, Drapetes muscosa, included with the pollen of these plants in the earliest record, is no longer a constituent of the flora but is limited only to subantarctic Chile. Available evidence indicates that plants survived the last glaciation north of the glacial border with the course of postglacial migration southward following the wastage of the glacier complex. Holocene climatic and vegetational changes in the Cordillera Pelada are interpreted in the context of regional reconstructions which show maximum warmth about 9000 yr ago with a pronounced dry period lasting from 9000 to 6500 yr B.P. Maximum precipitation was later reached around 4000 yr ago but has decreased overall since then. The regional decline of the endemic gymnosperm Fitzroya cupressoides, which today is extensively destroyed in the Cordillera Pelada, follows this decrease in precipitation. These climatic data suggest a net south ward shift in the zone of westerly winds that bring rainfall to the region over the past 4000 yr.
Concerning K–Ar Dating of a Basalt Flow from the Tahoe-Tioga Interglaciation, Sawmill Canyon, Southeastern Sierra Nevada, California
Authors: Dalrymple G. Brent , Burke R. M. , Birkeland Peter W. 
Published: December 2004

AbstractNew K–Ar ages for a basalt flow interbedded with Tahoe and Tioga tills in Sawmill Canyon, southeastern Sierra Nevada, slightly refine previously published ages for the flow and provide an estimate of 53,000 ± 44,000 yr for the Tahoe-Tioga interglaciation.
Multiple Deglaciations of the Hudson Bay Lowlands, Canada, Since Deposition of the Missinaibi (Last-Integlacial?) Formation
Authors: Andrews J. T. , Shilts W. W. , Miller G. H. 
Published: December 2004

AbstractThe stratigraphic record in the James and Hudson Bay Lowlands indicates that the sequence of glacial events at the geographical center of the 12.6 × 106km2Laurentide Ice Sheet may have been more complex than hitherto imagined. Isoleucine epimerization ratios ofin situand transported shells recovered from till and associated marine and fluvial sediments cluster into at least 4 discrete groups. Two alternative explanations of the data are offered, of which we strongly favor the first.Hypothesis 1:Setting the age of the “last interglacial” marine incursion, the Bell Sea, at 130,000 yr B.P. results in a long-term average diagenetic temperature for the lowlands of +0.6°C. Using this temperature enables us to predict the age of shells intermediate in age between the “last interglaciation” and the incursion of the Tyrrell Sea 8000 yr ago. Between these two interglacial marine inundations, Hudson Bay is predicted to have been free of ice along its southern shore about 35,000, 75,000, and 105,000 yr ago based on amino acid ratios from shells occurring as erratics in several superimposed tills and fluvial sediments. These results suggest (1) that traditional concepts of ice-sheet build-up and decay must be reexamined; (2) that “high” sea levels may have occurred during the Wisconsin Glaciation; and (3) that a critical reappraisal is required of the open ocean δ18O record as a simple indicator of global ice volume. Analternative, Hypothesis 2, is also examined. It is based on the assumption that the 35,000-yr-old deposits calculated on the basis of Hypothesis 1 date from the “last interglaciation”; this, in effect, indicates that the Missinaibi Formation, commonly accepted as sediments of the “last interglaciation,” are about 500,000 yr old and that the effective diagenetic temperature in the lowlands during approximately the last 130,000 yr has been close to −6°C. We argue for rejection of this alternative hypothesis.
Late Pleistocene Vegetation of Kings Canyon, Sierra Nevada, California
Authors: Cole Kenneth 
Published: December 2004

AbstractSeven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifersJuniperus occidentalis, Pinuscf.ponderosa, andP. monophylla. The pollen spectra of these Pleistocene middens are dominated byPinussp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), andArtemisiasp. Mesophytic conifers are represented by low macrofossil concentrations.Sequoiadendron giganteumis represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages.The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest thatS. giganteumgrew at lower elevations along the western side of the range and thatP. monophyllawas more widely distributed in cismontane California during the Pleistocene.