bluuebunny/crossref_metadata_2025_split huggingface dataset:
Age of Pre-late-Wisconsin Glacial-Estuarine Sedimentation, Bristol Bay, Alaska
Authors: Kaufman Darrell S. , Forman Steven L. , Lea Peter D. , Wobus Cameron W. 
Published: September 2002

AbstractPleistocene glacial-estuarine sediment deposited in an intertidal environment of northeastern Bristol Bay, southwestern Alaska, was dated using a variety of approaches, including infrared stimulated and thermoluminescence (IRSL and TL) techniques. Analysis of modern and14C-dated Holocene tide-flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation, thereby lending confidence to ages obtained from similar Pleistocene deposits by luminescence techniques. IRSL seems to be especially well suited for dating, with resolution on time scales of <10,000 yr. The ages of tide-flat mud of the Nushagak Formation, derived from the Ahklun Mountains to the northwest of Bristol Bay, and of Halfmoon Bay drift, derived from the Alaska Peninsula to the southeast, suggest contemporaneous glacial-estuarine deposition related to independent glacial source areas about 75,000–80,000 yr ago. This age is consistent with other geochronological data that indicate a pre-late-Wisconsin and post-substage-5e age, including nonfinite14C ages, a lack of interglacial indicators, and Old Crow tephra (∼140,000 yr) atop the drift, normal paleomagnetic inclinations, and amino acid (isoleucine) epimerization ratios (aIle/Ile). AIle/Ile ratios inPortlandia arctica(0.052 ± 0.003) from a marine-lag horizon at South Naknek beach, which separates Halfmoon Bay drift above from older glacial-estuarine drift below, are only slightly higher than inMya truncata(0.041 ± 0.007) from last-interglacial Pelukian deposits at Nome. As laboratory heating experiments show that the two genera epimerize at similar rates, these data imply correlation of the marine lag at South Naknek beach with Pelukian deposits. Hence, glaciers on the Alaska Peninsula experienced major pre-late-Wisconsin advances both before and after the last interglaciation. Shells reworked into Halfmoon Bay drift yield aIle/Ile ratios of 0.028 ± 0.005 forPortlandiaat Second Point and 0.027 ± 0.001 forHiatella arcticaat Etolin Point. Together with assumptions about the postdepositional temperature history, these ratios indicate that the shells are at least 55,000 yr, and probably closer to ∼90,000 yr, although the uncertainty in this age estimate is broad. The amino acid and luminescence data converge on an age between about 75,000, and 90,000 yr, late during oxygen-isotope stage 5, for a major ice advance far beyond late-Wisconsin limits.
Quaternary Sedimentary Processes and Budgets in Orphan Basin, Southwestern Labrador Sea
Authors: Hiscott Richard N. , Aksu Ali E. 
Published: September 2002

AbstractThe continental slope in Orphan Basin, northeast of Newfoundland, is underlain by several seaward-thinning debris-flow wedges alternating with acoustically stratified, regionally extensive, mainly hemipelagic sediments. δ18O stratigraphy and volcanic ash layers in a 11.67-m core indicate that the uppermost debris-flow wedge formed during the last of several sea-level lowstands in isotopic stages 2–4. Similarly, seismic reflection correlation of dated levels at DSDP Site 111 with the Orphan Basin succession suggests that two deeper debris-flow wedges were deposited during oxygen isotopic stages 6 and 8. The oldest of the debris-flow deposits in at least three of the wedges formed well into the corresponding glacial cycle, after ice sheets had reached the edge of the continental shelf. Slower deposition by hemipelagic processes and ice rafting formed the acoustically stratified units, including Heinrich layers. The youngest three debris-flow wedges each have volumes of 1300–1650 km3. Approximately two-thirds of this material is attributed to glacial erosion of Mesozoic and Tertiary strata beneath the Northeast Newfoundland Shelf. The remainder is believed to have been derived by glacial erosion of older bedrock that now forms the island of Newfoundland. The observed sediment volumes and the inferred basal and upper ages of the debris-flow wedges imply an average glacial denudation rate of about 0.13 mm/yr for this older bedrock, and an average of about 60 m of glacial bedrock erosion since oxygen isotope stage 22. This denudation rate is similar to estimates from the Barents Sea region off Norway.
Boreal Ecosystem Development in the Northwestern Alaska Range since 11,000 yr B.P.
Authors: Hu Feng Sheng , Brubaker Linda B. , Anderson Patricia M. 
Published: September 2002

AbstractAnalyses of pollen, plant macrofossils, macroscopic charcoal, mollusks, magnetic susceptibility, and geochemical content of a sediment core from Farewell Lake yield a 11,000-yr record of terrestrial and aquatic ecosystem changes in the northwestern foothills of the Alaska Range. Between 11,000 and 8500 yr B.P., the regional landscape was dominated by aBetulashrub tundra, in whichPopulus-Salixcommunities were common. Abundant charcoal in sediments indicates that fires were common in the lake catchment during this period, and high mineral accumulation rates, allogenic elemental content, and magnetic susceptibility suggest intense soil erosion. In addition, mollusks, pollen and macrofossils of aquatic macrophytes, and biogenic silica provide evidence that the lake was substantially shallower and more productive 11,000–8500 yr B.P. than later. Low lake level and high aquatic productivity might have been caused by warm and dry summers associated with early postglacial insolation maximum in northern high latitudes. About 8000 yr B.P.,Picea glaucaarrived within the lake catchment, forming a forest tundra association until ca. 6000 yr B.P.Alnusshrub thickets established in the region ca. 6500 yr B.P., andBetula papyriferaarrived ca. 6000 yr B.P. ClosedP. glaucaforests developed ca. 6000 yr B.P.Picea marianabecame important subsequently and replacedP. glaucaas the dominant tree species in the region ca. 4000 yr B.P. An increase in authigenic Fe/Mn ratios suggests that the development of waterlogged soils accompanied this vegetation change. Fires increased in importance at this time and might have accelerated soil erosion. The establishment ofP. marianaforests probably reflected complex responses of forest ecosystems to the onset of cooler and wetter climate conditions during the late Holocene.
Nonassociation of Paleoindians with AMS-Dated Late Pleistocene Mammals from the Dutchess Quarry Caves, New York
Authors: Steadman David W. , Stafford Thomas W. , Funk Robert E. 
Published: September 2002

AbstractAMS14C ages of 10 bones of the caribou (Rangifer tarandus), flat-headed peccary (Platygonus compressus), and giant beaver (Castoroides ohioensis) from the Dutchess Quarry Caves, New York, range from 13,840 ± 80 to 11,670 ± 70 yr B.P. No bones from any of these species are demonstrably associated with Paleoindian artifacts (fluted points) or other cultural materials from the sites because the bones lack unequivocal stratigraphic association with artifacts, as well as physical (taphonomic) evidence for human association (e.g., burning, cut marks, distinctive breakage). Together with the Holocene conventional14C dates of charcoal and the varied stratigraphic proveniences of the fluted points and the dated bones, the new AMS14C dates argue that most strata at the Dutchess Quarry Caves contain a mixture of late Pleistocene and Holocene materials. This mixing probably resulted from post-depositional bioturbation (by humans, rodents, carnivores, and scavengers) and cryoturbation (annual freeze–thaw cycles). Rather than being of cultural origin, the bones of caribou, flat-headed peccary, and giant beaver likely were deposited in the Dutchess Quarry Caves by nonhuman predators or scavengers, such as ursids, canids, felids, condors, or eagles.
Tephrochronologic Constraints on the Late Pleistocene History of the Southern Margin of the Cordilleran Ice Sheet, Western Washington
Authors: Begét James E. , Keskinen Mary J. , Severin Kenneth P. 
Published: September 2002

An ash layer that appears geochemically correlative with Mt. St. Helens tephra set S occurs in a sequence of Pleistocene lake sediments in the Ohop Valley of the southern Puget Lowland, below Vashon till deposited during the maximum late Pleistocene advance (Fraser Glaciation) of the Puget Lobe of the Cordilleran Ice Sheet. The Puget Lobe reached its maximum southern extent ca. 14,000–14,500 yr B.P., and at least part of set S is evidently somewhat older. Previous radiocarbon and thermoluminescence dates for set S have ranged from 13,000 to 16,000 yr B.P.Geochemically correlative deposits of set S tephra occur in slackwater sediments coeval with the Missoula Floods in eastern Washington, produced by jökulhlaups through the Purcell Trench Lobe of the Cordilleran Ice Sheet. These relationships suggest that advances of glacier lobes on the southern margin of the Cordilleran Ice Sheet were nonsynchronous, as the Pucell Trench lobe east of the Cascade Range advanced to its maximum southern extent prior to the time of the eruption of set S, before the Puget Lobe west of the Cascades reached its maximum southern extent.
Late-Glacial to Early Holocene Climate Changes from a Central Appalachian Pollen and Macrofossil Record
Authors: Kneller Margaret , Peteet Dorothy 
Published: September 2002

AbstractA late-glacial to early Holocene record of pollen, plant macrofossils, and charcoal has been obtained from two cores from Browns Pond in the central Appalachians of Virginia. An AMS radiocarbon chronology defines the timing of moist and cold excursions, superimposed on the overall warming trend from 14,200 to 750014C yr B.P. This site had cold, moist conditions from ca. 14,200 to 12,70014C yr B.P., with warming at 12,730, 11,280, and 10,05014C yr B.P. A decrease in deciduous broad-leaved tree taxa andPinus strobus(haploxylon) pollen, simultaneous with a reexpansion ofAbies,denotes a brief, cold reversal from 12,260 to 12,20014C yr B.P. A second cold reversal, inferred from increases in montane conifers, is centered at 750014C yr B.P. The cold reversals at Browns Pond may be synchronous with climate change in Greenland and northwestern Europe. Warming at 11,28014C yr B.P. shows the complexity of regional climate responses during the Younger Dryas chronozone.
Cyclic Aggradation and Downcutting, Fluvial Response to Volcanic Activity, and Calibration of Soil-Carbonate Stages in the Western Grand Canyon, Arizona
Authors: Lucchitta Ivo , Curtis Garniss H. , Davis Marie E. , Davis Sidney W. , Turrin Brent 
Published: September 2002

AbstractIn the western Grand Canyon, fluvial terraces and pediment surfaces, both associated with a Pleistocene basalt flow, document Quaternary aggradation and downcutting by the Colorado River, illuminate the river's response to overload and the end of overload, and allow calibration of soil-carbonate stages and determination of downcutting rates. Four downcutting–aggradation cycles are present. Each begins with erosion of older deposits to form a new river channel in which a characteristic suite of deposits is laid down. The current cycle (I) started ∼700 yr B.P. The oldest (IV) includes the 603,000 ± 8000 to 524,000 ± 7000 yr Black Ledge basalt flow, emplaced when the river channel was ∼30 m higher than it is now. The flow is overlain by basalt–cobble gravel and basalt sand. Soils reach the stage V level of carbonate development. Calibrated ages for soil stages are Stage V, ∼525,000 yr; stage IV, <525,000 yr, ≥250,000 yr; stage III, <250,000 yr, ≥100,000 yr. The monolithologic basalt sand beds represent overloading by volcanic ash produced by an eruption 30–50 km upstream. The basalt–cobble beds signal breaching and rapid destruction of lava dams and erosion of flows. These deposits show that the Colorado River responds to overload by aggrading vigorously during the overload and then downcutting equally vigorously when the overload ends. The overall downcutting rate for the interval studied is 1.6 cm/1000 yr, much lower than rates upstream. The current downcutting rate, 11–14 m/1000 yr, likely is a response both to the end of late Pleistocene and early Holocene overload and to the reduction of sediment supply caused by Glen Canyon Dam.
African Monsoonal Precipitation Modulated by Interhemispheric Temperature Gradients
Authors: Mulitza Stefan , Rühlemann Carsten 
Published: September 2002

AbstractThe deglacial pattern of a high-resolution alkenone-derived temperature record from the southeastern tropical Atlantic was compared with one from the northeastern subtropical Atlantic. During Termination 1b, surface waters in the eastern tropical Atlantic (6°S) reached modern temperatures, whereas those in the subtropical northeastern Atlantic (21°N) were still considerably colder than today. This asymmetrical warming may reflect meltwater-induced reductions in the northward heat transport and helps to explain rapid changes in monsoonal precipitation over Africa during the early Holocene.
14,000 Years of Sediment, Vegetation, and Water-Level Changes at the Makepeace Cedar Swamp, Southeastern Massachusetts
Authors: Newby Paige E. , Killoran Peter , Waldorf Mahlon R. , Shuman Bryan N. , Webb Robert S. , Webb Thompson 
Published: September 2002

AbstractData from a transect of four cores collected in the Makepeace Cedar Swamp, near Carver, Massachusetts, record past changes in deposition, vegetation, and water level. Time series of palynological data provide a 14,000-yr record of regional and local vegetation development, a means for biostratigraphic correlation and dating, and information about changes in water level. Differences in records among cores in the basin show that water level decreased at least 1.5 m between ∼10,800 and 9700 cal yr B.P., after which sediment accumulation was slow and intermittent across the basin for about 1700 yr. Between 8000 and 5600 cal yr B.P., water level rose ∼2.0 m, after which slow peat accumulation indicates a low stand about the time of the hemlock decline at 5300 ± 200 cal yr B.P. Dry conditions may have continued after this time, but by 3200 cal yr B.P., the onset of peat accumulation in shallow cores indicates that water level had risen to close to its highest postglacial level, where it is today. Peat has accumulated across the whole basin since 3200 cal yr B.P. Data from Makepeace and the Pequot Cedar Swamp, near Ledyard, Connecticut, indicate an early Holocene dry interval in southern New England that began 11,500 yr ago near the end of the Younger Dryas interval. The dry conditions prevailed between 10,800 and 8000 cal yr B.P. and coincide with the arrival and later rise to dominance of white pine trees (Pinus strobus) both regionally and near the basins. Our results indicate a climatic cause for the “pine period” in New England.
Late-Glacial Cooling in Amazonia Inferred from Pollen at Lagoa do Caçó, Northern Brazil
Authors: Ledru Marie-Pierre , Cordeiro Renato Campello , Dominguez José Maria Landim , Martin Louis , Mourguiart Philippe , Sifeddine Abdelfetah , Turcq Bruno 
Published: September 2002

AbstractNew pollen data from a core at Lagoa do Caçó, Maranhão state, Brazil (2°58′S 43°25′W; 120 m elevation), show higher frequencies of Podocarpus at the end of the Pleistocene than today. The increase in Podocarpus, which follows the successive increase of various pioneer species such as Didymopanax, Melastomataceae/Combretaceae, and Cecropia, implies a progressive late-glacial increase of moist and cool climatic conditions. A comparable increase in Podocarpus is found in other lowland records in Amazonia. A review of published pollen data from Amazonia suggests that the moisture source was from the southeast. By contrast, present-day moisture comes from the tropical Atlantic and from the Amazon basin, with its convective precipitation. The likely cause for the southeastern moisture source between ca. 15,000 and 14,500 cal yr B.P. was enhanced polar (Antarctic) advection that reached low latitudes and maintained year-round the meteorological equator in its austral-winter position at northern latitudes or reduced drastically its southward summer displacement. This hypothesis is consistent with marine and ice core records.
Carbon-Isotope, Diatom, and Pollen Evidence for Late Holocene Salinity Change in a Brackish Marsh in the San Francisco Estuary
Authors: Byrne Roger , Ingram B. Lynn , Starratt Scott , Malamud-Roam Frances , Collins Joshua N. , Conrad Mark E. 
Published: September 2002

AbstractAnalysis of diatoms, pollen, and the carbon-isotopic composition of a sediment core from a brackish marsh in the northern part of the San Francisco Estuary has provided a paleosalinity record that covers the past 3000 yr. Changes in marsh composition and diatom frequencies are assumed to represent variations in freshwater inflow to the estuary. Three periods of relatively high salinity (low freshwater inflow) are indicated, 3000 to 2500 cal yr B.P., 1700 to 730 cal yr B.P., and ca. A.D. 1930 to the present. The most recent period of high salinity is primarily due to upstream storage and water diversion within the Sacramento–San Joaquin watershed, although drought may also have been a factor. The two earlier high-salinity periods are likely the result of reduced precipitation. Low salinity (high freshwater flow) is indicated for the period 750 cal yr B.P. to A.D. 1930.
Biogenic Silica Record of the Lake Baikal Response to Climatic Forcing during the Brunhes
Authors: Prokopenko Alexander A. , Karabanov Eugene B. , Williams Douglas F. , Kuzmin Mikhail I. , Shackleton Nicholas J. , Crowhurst Simon J. , Peck John A. , Gvozdkov Alexander N. , King John W. 
Published: September 2002

AbstractThis work presents a detailed, orbitally tuned biogenic silica record of continental paleoclimate change during the Brunhes chron. The Brunhes/Matuyama boundary lies within the warm isotopic stage 19 in Baikal, and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record. The high amplitude and resolution of climatically driven changes in BioSi content in Lake Baikal sediments permits tuning of almost every precessional cycle during the Brunhes and reveals the structure of interglacial stages. For example, the last three interglacial stages (MIS 5, 7, and 9) clearly consist of five substages (a, b, c, d, e) corresponding to precessional insolation peaks. Abrupt and intense regional glaciations in Siberia during substages 5d and 7d were driven by extreme insolation minima. During substage 9d cooling was more gradual in response to more moderate forcing. The impact of strong glaciation is also observed in the middle of stage 15, where full glacial conditions appear to have lasted for over 30,000 yr during substages 15d, 15c, and 15b. Marine oxygen isotopic stage 11 appears to be the warmest period during the Brunhes in the Lake Baikal record, with at least three substages.A new hypothesis is presented regarding the response of the Lake Baikal BioSi record to insolation forcing. Based on the mechanism controlling modern diatom blooms, biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column. This mechanism is also sensitive to short-term sub-Milankovich cooling events, such as the mid-Eemian cooling, the Montaigu event during substage 5c, and a cooling which appears to be analogous to the Montaigu event during substage 9c. The continuity of the Lake Baikal paleoclimate record, its sensitivity to orbital forcing, and its high resolution make it an excellent candidate for a new “paleoclimatic stratotype” section for continental Asia.
Late Quaternary Inland Dunes of Southern Louisiana and Arid Climate Phases in the Gulf Coast Region
Authors: Otvos Ervin G. , Price David M. 
Published: September 2002

AbstractThirty-five sand hills that form six scattered groups rise abruptly from the flat late Pleistocene coastal plain in southeastern Louisiana. New studies confirm their eolian origin. For the first time, several late Wisconsin to early Holocene episodes of arid climate conditions have been recognized and dated in this currently humid warm-temperate subtropical region. Periods of dune formation and reactivation (28,800 to 7900 yr B.P.) were determined by the thermoluminescence method. The onset of the current climate in this Gulf coastal region postdates early Holocene time. The textural and structural homogeneity of the ridge lithosomes, good sorting of their sand fraction, and the dominantly orange hues of the dune sediments contrast with the underlying yellowish–brown to light-brown sandy silts and the well-stratified, occasionally gravelly sands of the underlying alluvial Prairie Formation. Sharply defined, unconformable ridge bases; symmetrical, oval, occasionally parabolic mound shapes; and steep slopes confirm the dune origins. The dominant orientations of ridges and ridge chains clearly reflect paleowind directions. Age comparison with dunes of the lower Mississippi Valley, the northeastern–eastern Gulf of Mexico coast, and south Atlantic coastal areas confirms the existence of at least seasonally dry climate conditions from early Wisconsin to middle Holocene times. The onset of the modern humid-subtropical climate phase in this region thus dates back only to the middle Holocene.
Terminal Pleistocene/Early Holocene Environmental Change at the Sunshine Locality, North-Central Nevada, U.S.A.
Authors: Huckleberry Gary , Beck Charlotte , Jones George T. , Holmes Amy , Cannon Michael , Livingston Stephanie , Broughton Jack M. 
Published: September 2002

AbstractSedimentological, faunal, and archaeological investigations at the Sunshine Locality, Long Valley, Nevada reveal a history of human adaptation and environmental change at the last glacial–interglacial transition in North America's north-central Great Basin. The locality contains a suite of lacustrine, alluvial, and eolian deposits associated with fluvially reworked faunal remains and Paleoindian artifacts. Radiocarbon-dated stratigraphy indicates a history of receding pluvial lake levels followed by alluvial downcutting and subsequent valley filling with marsh-like conditions at the end of the Pleistocene. A period of alluvial deposition and shallow water tables (9,800 to 11,00014C yr B.P.) correlates to the Younger Dryas. Subsequent drier conditions and reduced surface runoff mark the early Holocene; sand dunes replace wetlands by 8,00014C yr B.P. The stratigraphy at Sunshine is similar to sites located 400 km south and supports regional climatic synchroneity in the central and southern Great Basin during the terminal Pleistocene/early Holocene. Given regional climate change and recurrent geomorphic settings comparable to Sunshine, we believe that there is a high potential for buried Paleoindian features in primary association with extinct fauna elsewhere in the region yet to be discovered due to limited stratigraphic exposure and consequent low visibility.