bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tectonic Speleogenesis of Devils Hole, Nevada, and Implications for Hydrogeology and the Development of Long, Continuous Paleoenvironmental Records
Authors: Riggs Alan C. , Carr W.J. , Kolesar Peter T. , Hoffman Ray J. 
Published: September 2002

AbstractDevils Hole, in southern Nevada, is a surface collapse into a deep, planar, steeply dipping fault-controlled fissure in Cambrian limestone and dolostone. The collapse intersects the water table about 15 m below land surface and the fissure extends at least 130 m deeper. Below water, most of the fissure is lined with a >30-cm-thick layer of dense maxillary calcite that precipitated continuously from groundwater for >500,000 yr. The thick mammillary calcite coat implies a long history of calcite-supersaturated groundwaters, which, combined with the absence of dissolutional morphologies, suggests that Devils Hole was not formed by karst processes. Devils Hole is located in a region of active extension; its tectonic origin is shown by evidence of spreading of its planar opening along a fault and by the orientation of its opening and others nearby, perpendicular to the northwest-southeast minimum principal stress direction of the region. Most Quaternary tectonic activity in the area, including seismicity and Quaternary faults and fractures, occurs on or parallel to northeast-striking structures. The hydrogeologic implications of this primarily structural origin are that fracture networks and caves opened by extensional tectonism can act as groundwater flowpaths functionally similar to those developed by karst processes and that, during active extension, transmissivity can be maintained despite infilling by mineral precipitation. Such extensional environments can provide conditions favorable for accumulation of deposits preserving long, continuous paleoenvironmental records. The precipitates in Devils Hole store chronologies of flow system water-level fluctuations, hydrochemistry, a half-million-yr proxy paleoclimate record, evidence of Devils Hole's tectonic origin, and probably atmospheric circulation.
Long Pleistocene Pollen Records from the Praclaux Crater, South-Central France
Authors: Reille Maurice , de Beaulieu Jacques-Louis 
Published: September 2002

AbstractA 46-m core of lake sediments, obtained from the center of the explosion crater of Praclaux (Haute-Loire, Velay, France), was studied on the basis of 368 pollen spectra. Five temperate forest episodes alternating with phases indicative of glacial climates are recorded. Two of these episodes show vegetation successions representative of full interglaciations; the oldest is contemporaneous with the Holsteinian interglaciation. A thick trachytic tephra permits correlation to be established with the pollen sequence from Lac du Bouchet. This comparison indicates the presence of two complete interglaciations between the Holsteinian and the Eemian that are the equivalents of marine isotope stages 7 and 9. The Holsteinian therefore corresponds to isotope stage 11.
Simulating Magnetic Susceptibility Profiles in Loess as an Aid in Quantifying Rates of Dust Deposition and Pedogenic Development
Authors: Anderson Robert S. , Hallet Bernard 
Published: September 2002

AbstractMagnetic susceptibility profiles χ(z) in loess sequences reflect a combination of two climatically modulated processes: dust deposition and pedogenic development. Prominent soils with high χ values, for example, likely reflect periods of slow dust deposition, and warm wet conditions favorable for rapid chemical weathering. To refine our understanding of the climate records contained in loess, we develop a numerical model as a tool for exploring quantitatively the integrated record of the temporal variation in rates of loess aggradation and soil development contained in χ profiles. In our model, the aggrading loess is pedogenically altered in a reactive zone near the ground surface. The strength of the χ signal is dictated by both the depth-dependent intensity of pedogenic processes and the rate of dust accumulation, which dictates the total time a loess parcel spends in the near-surface reactive zone. The model can accommodate both pedogenic production of magnetically susceptible minerals and arrival of magnetically susceptible grains as eolian dust. To explore the model performance and develop a sense of time and length scales implicit in χ profiles, we first examine simple synthetic cases with idealized steady and cyclic climatic forcing. Reported χ profiles in three Chinese loess sequences at varying distances from the western China dust source are then modeled in two illustrative ways: (i) by imposing a specific dust deposition rate history that is proportional to the dust accumulation rate history reported from western Pacific deep-sea cores, allowing the time variation of pedogenic rates to be calculated directly from χ profiles; and (ii) by imposing both dust accumulation and pedogenic rate histories that are independently scaled by the deep-sea δ18O history, which reflects global climate cycles to which regional climate forcing is linked. We find that the zone of pedogenic activity is roughly 0.5–1.0 m thick, both deposition rate and pedogenic intensity have varied dramatically over the last 140,000 yr, the age structure of the Luochuan loess sequence is best fit by driving the model with the δ18O record, and environmental conditions must have been anomalously favorable for pedogenesis during isotope stage 3 at all three sites. Finally, we advocate the assembly of a variety of data types at a suite of sites within any loess field that taken together will better constrain the temporal and spatial patterns of climatically modulated deposition and pedogenic processes.
Implications for Deglaciation Chronology from New AMS Age Determinations in Central West Greenland
Authors: van Tatenhove Frank G. M. , van der Meer Jaap J. M. , Koster Eduard A. 
Published: September 2002

AbstractNew evidence has been obtained for the age of the Umı̂vı̂t/Keglen and Ørkendalen moraine systems close to the present ice sheet margin in central West Greenland. The Umı̂vı̂t/Keglen moraine system is dated at 7500 to 650014C yr B.P., which is older than the previously assumed date of 7300 to 600014C yr B.P. The Ørkendalen system is now dated at 6200 to 560014C yr B.P. against earlier estimates of 300 to 70014C yr B.P. The new age is based on AMS radiocarbon-dated organic material within depressions between morainic ridges belonging to the Ørkendalen system. A major implication of the new age is that ice margin positions prevailed for about 6000 years behind the present ice sheet margin. The retreat behind the present margin could be substantial, and in the light of deglaciation rates prior to the Ørkendalen phase, may be ca. 10's of kilometers rather than kilometers. Circumstantial evidence is found for the retreat of the ice sheet margin behind its present position during the Holocene climatic optimum. The results, placed into a time frame of deglaciation since the last glacial maximum, enable comparison with Greenland ice sheet models and ice core records.
Point-Counting Technique for Fission-Track Dating of Tephra Glass Shards, and Its Relative Standard Error
Authors: Bigazzi Giulio , Galbraith Rex F. 
Published: September 2002

AbstractFission-track dating of glass is potentially an efficient technique for tephrochronological studies. However, most glasses from Quaternary tephra have very low spontaneous track densities and track counting is laborious. The point-counting technique is a simplified procedure for evaluating fission-track areal densities in a glass shard population that allows the analyst to count larger numbers of tracks in significantly shorter times. A field of view is coded as 1 if its center is on glass and is 0 otherwise, and the total area of glass is estimated by counting the number of 1's. Under simple assumptions, the binomial distribution appears to provide a reasonable evaluation of the additional experimental error in a fission-track density determination by this technique. Glass shard populations have been simulated, assuming that glass areas are random samples from distributions analogous to real ones. The effect of variation in glass area on the relative standard error of the estimated track density is found to be small. The point-counting technique significantly enhances the potential of fission-track dating, especially for very low track densities typical of most Quaternary tephra, as the additional error associated with its use is largely counterbalanced by the greater number of tracks that can be counted.
Timing of the Last-Interglacial High Sea Level on the Seychelles Islands, Indian Ocean
Authors: Israelson Carsten , Wohlfarth Barbara 
Published: September 2002

AbstractCorals from the Seychelles Islands, Indian Ocean, occur mainly as small coralline algae–vermetid remnants found in cavities adhering to the rock surface, and they rarely attain more than 2 m2 in area. Samples of Goniastrea and Porites from elevations between 1.7 and 6 m above present mean sea level were dated by TIMS 238U–234U–230Th techniques. The ages from well-preserved corals lie between 131,000 and 122,000 yr B.P., in agreement with most other observations of the last-interglacial sea level. Field evidence and dating from high marine limestones from two sections at La Digue Island indicate a period of coral buildup until 131,000 yr B.P., followed by a drop in sea level between 131,000 and 122,000 yr B.P.
A Holocene Record of Atmospheric Dust Deposition on the Penny Ice Cap, Baffin Island, Canada
Authors: Zdanowicz Christian M. , Zielinski Gregory A. , Wake Cameron P. , Fisher David A. , Koerner Roy M. 
Published: September 2002

AbstractAn >11,550-yr-long record of atmospheric dust deposition was developed from an ice core (P95) drilled through the Penny ice cap, Baffin Island. The P95 record documents environmental changes that affected the production and transport of dust in the eastern Canadian Arctic during the late Pleistocene and Holocene. Dust deposition on the Penny ice cap was greatest in late-glacial time when the climate was dry and windy and comparatively low in the Holocene. Microparticles deposited during late-glacial time are finer than in Greenland cores, suggesting distinct dust sources and transport trajectories to each region. Dust deposition at the P95 site increased after ca. 7800 yr ago as the Penny ice cap receded and distance from local dust sources was reduced. Deflation of newly exposed marine sediments on southwestern Baffin Island may have contributed to this dust increase. The P95 and GISP2 (Greenland) dust records show diverging trends in the middle to late Holocene, reflecting the growing influence of regional environmental conditions (e.g., dust source area, snow cover extent) on atmospheric dust deposition. This study further demonstrates how valuable records of regional-scale paleoenvironmental changes can be developed from small circum-Arctic ice caps, even those affected by considerable melt.
Holocene Earthquakes Inferred from a Fan-Delta Sequence in the Dead Sea Graben
Authors: Enzel Yehouda , Kadan Galit , Eyal Yehuda 
Published: September 2002

AbstractThe Holocene sequence of the fan-delta of Nahal Darga, in Israel, records deformation associated with earthquakes related to the Dead Sea Transform in general and to the Jericho Fault in particular. The fan-delta sequence is well exposed, and 20 radiocarbon ages help to date the earthquakes that are inferred from (a) displacement along faults, (b) liquefaction features associated with 11 separate sandy and silty layers, and (c) slumped allocthonous bodies of sediments located directly above one of the main splays of the Jericho Fault. On average, an earthquake larger thanM5.5 has occurred approximately every 600 years. This estimate is based on the earthquake record of the complete stratigraphic sequence, with erosional hiatuses omitted from the calculations. The most recently deformed layer is related to the 1927 Jericho (ML6.2) earthquake. This layer provides a modern analog for the style of soft-sediment deformation associated with earthquakes in the late Pleistocene and Holocene silty sand beds of the fan-delta complexes of the Dead Sea and its predecessor, Lake Lisan.
North Atlantic Climate–Ocean Variations and Sea Level in Long Island Sound, Connecticut, Since 500 cal yr A.D.
Authors: van de Plassche Orson 
Published: September 2002

AbstractA record of detrended mean high water (MHW) variations from Hammock River marsh, Connecticut, is extended from ca. 850 to ca. 500 cal yr A.D. and correlated with summer-temperature reconstructions from northern Fennoscandia and northern Eurasia, Greenland Ice Sheet Project 2 δ18O, and Greenland Ice Core Project borehole-temperature variations from central Greenland, a Sargasso Sea sea-surface temperature (SST) record, and a proxy record for deep-ocean flow south of Iceland. The records from northern Fennoscandia/Eurasia and central Greenland document century-scale intervals of warming (four) and cooling (three) since ca A.D. 850. The MHW fluctuations lag behind these climate intervals by 0–100 yr, with the two larger MHW rises corresponding to the two larger temperature increases. This positive correlation suggests that surface air temperature (SAT) is a dominant variable controlling sea level in the northwestern North Atlantic since ca. A.D. 850. The SST variations parallel the MHW fluctuations back to ca. 950 cal yr A.D. A positive correlation is found also for (sub)century-scale SAT and MHW variations during the period A.D. 500–850, but this result is less firm. MHW–SST correlation over this time interval is not consistent.
Speleothem Evidence for Changes in Indian Summer Monsoon Precipitation over the Last ∼2300 Years
Authors: Denniston Rhawn F. , González Luis A. , Asmerom Yemane , Sharma Ram H. , Reagan Mark K. 
Published: September 2002

AbstractSpeleothems from a well-ventilated dolomitic cave in the Pokhara Valley, central Nepal, preserve a mineralogic record of Indian summer monsoon variability over the past 2300 yr. Annually deposited aragonite layers formed between 2300 and 1500 yr B.P., indicating reduced monsoon precipitation and increased cave aridity, whereas alternating calcite/aragonite laminae deposited after 1500 yr B.P. record elevated summer monsoon precipitation and increased cave humidity. Dense, optically clear calcite layers deposited from 450 ± 5 to 360 ± 20 yr B.P. (1550 to 1640 A.D.) indicate a less-evaporative cave environment and suggest moister and/or cooler conditions, possibly related to climatic change associated with the onset of the Little Ice Age.
Holocene Foraminifera as Indicators of Relative Estuarine-Lagoonal and Oceanic Influences in Estuarine Sediments of the River Murray, South Australia
Authors: Cann John H. , Bourman Robert P. , Barnett Elizabeth J. 
Published: September 2002

AbstractIn southeastern South Australia, the River Murray debouches through a coastal barrier separating euryhaline estuarine-lagoonal waters from the Southern Ocean. Depending upon the relative freshwater outflow of the river and ingress of the ocean, water salinity varies greatly within the lower estuary.Ammonia beccariiandElphidium articulatumare euryhaline species of foraminifera that characterize the estuary and back-barrier Coorong Lagoon. The inner-shelf marine environment hosts an assemblage in whichDiscorbis dimidiatus, E. crispum, E. macelliforme,and various cibicidid species predominate. In cored sediments recovered from the shallow lower estuary, the relative abundance ofA. beccarii + E. articulatumwas compared with that ofD. dimidiatus + E. crispum + E. macelliforme+ other species. These data, and AMS radiocarbon ages determined for foraminifera and ostracods, provide evidence of a change from maximum oceanic influence (5255 ± 60 yr B.P.) to maximum estuarine influence (3605 ± 70 yr B.P.). Over this same time interval, sea level fell relatively by about 2 m. However, the event was also contemporaneous with falling water levels in several Victorian lakes, and it is thus attributed to onset of climatic aridity. Reduced precipitation in the River Murray catchment and reduced freshwater outflow enhanced development of the flood-tide delta and constriction of the mouth.
Holocene Climate Inferred from Oxygen Isotope Ratios in Lake Sediments, Central Brooks Range, Alaska
Authors: Anderson Lesleigh , Abbott Mark B. , Finney Bruce P. 
Published: September 2002

AbstractAnalyses of sediment cores from two lakes in the central Brooks Range provide temperature and moisture balance information for the past ∼8500 cal yr at century-scale resolution. Two methods of oxygen isotope analysis are used to reconstruct past changes in the effective moisture (precipitation minus evaporation) and temperature. Effective moisture is inferred from oxygen isotope ratios in sediment cellulose from Meli Lake (area ∼0.13 km2, depth 19.4 m). The lake has a low watershed-to-lake-area ratio (7) and significant evaporation relative to input. Summer temperature shifts are based on oxygen isotope analyses of endogenic calcite from Tangled Up Lake (area ∼0.25 km2, depth 3.5 m). This basin has a larger watershed-to-lake-area ratio (91) and less evaporation relative to input. Sediment oxygen isotope analyses from the two sites indicate generally more arid conditions than present prior to ∼6000 cal yr B.P. Subsequently, the region became increasingly wet. Temperature variability is recorded minimally at centennial scale resolution with values that are generally cool for the past ∼6700 cal yr. The timing and direction of climate variability indicated by the oxygen isotope time series from Meli and Tangled Up lakes are consistent with previously established late Holocene glacier advances at ∼5000 cal yr B.P. in the central Brooks Range, and high lake-levels at Birch Lake since ∼5500 cal yr B.P. This unique use of oxygen isotopes reveals both moisture balance and temperature histories at previously undetected high-resolution temporal scales for northern Alaska during the middle to late Holocene.
Fossil Rotifers and the Early Colonization of an Antarctic Lake
Authors: Swadling Kerrie M. , Dartnall Herbert J. G. , Gibson John A. E. , Saulnier-Talbot Émilie , Vincent Warwick F. 
Published: September 2002

AbstractEarly Holocene sediments from a continental Antarctic lake (Ace Lake, Vestfold Hills, East Antarctica) contained abundant fossil rotifers of the genus Notholca. The fossil is similar to specimens of Notholca sp. present in modern-day Ace Lake and other fresh and brackish lakes of the Vestfold Hills. Cyanobacteria and protists (chrysophyte cysts, dinoflagellate cysts, and rhizopod tests) were also recovered from the core samples. These sediments were deposited early in the freshwater phase of Ace Lake, soon after deglaciation of the area. The occurrence of this trophically diverse assemblage of organisms at an early stage in the evolution of the lake suggests either that they were part of an endemic Antarctic flora and fauna which pre-dated the last glacial maximum and survived in glacial refugia or that efficient intercontinental dispersal had occurred.
Diatom, Pollen, and Chemical Evidence of Postglacial Climatic Change at Big Lake, South-Central British Columbia, Canada
Authors: Bennett Joseph R. , Cumming Brian F. , Leavitt Peter R. , Chiu Marian , Smol John P. , Szeicz Julian 
Published: September 2002

AbstractPostglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until ∼8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from ∼8500 to ∼7500 cal yr B.P. Slightly less arid conditions are inferred from ∼7500 until ∼6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At ∼6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until ∼3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until ∼6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P.
Radiocarbon Dating, Chronologic Framework, and Changes in Accumulation Rates of Holocene Estuarine Sediments from Chesapeake Bay
Authors: Colman Steven M. , Baucom Pattie C. , Bratton John F. , Cronin Thomas M. , McGeehin John P. , Willard Debra , Zimmerman Andrew R. , Vogt Peter R. 
Published: September 2002

AbstractRapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with 210Pb and 137Cs data and pollen stratigraphy from the same sites.Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.