bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Quaternary Glaciation of the Eastern Queen Elizabeth Islands, N.W.T., Canada: Alternative Models
Authors: England John
Published: December 2004

It has been suggested that during the last glaciation the Innuitian Ice Sheet existed over the eastern Queen Elizabeth Islands. This is based on the pattern of postglacial emergence over this area and the timing of driftwood penetration into the interisland channels. Alternative interpretations of both sets of data raise questions about the presence of the Innuitian Ice Sheet at this time. Field observations on northeastern Ellesmere Island, plus additional data pertaining to the presence of multiple tills and “old” radiometric dates on lacustrine deposits, shelly tills, and raised marine features suggest that the maximum glaciation over this region, equivalent to the Innuitian Ice Sheet, predates the last glaciation, Palaeoclimatic conditions are also discussed in relation to these data. It is suggested that during the last glaciation of the Queen Elizabeth Islands there was a convergent but not coalescent advance of the existing upland ice-fields. This noncontiguous ice cover over the Queen Elizabeth Islands is termed the Franklin Ice Complex. It is suggested that the term Innuitian Ice Sheet be reserved for contiguous older glaciations over this same area.
Magnetic Stratigraphy of Lake Michigan Sediments Obtained from Cores of Lacustrine Clay
Authors: Vitorello Icaro , Van der Voo Rob
Published: December 2004

Postglacial and lacustrine sediments from Lake Michigan have been paleomagnetically investigated. The primary goal was to test the feasibility of correlation between several cores in terms of their magnetic signatures. After alternating field and thermal demagnetizations, inclination and relative declination values were obtained that show characteristic short-term fluctuations. Major features, including changes in the magnetic intensity of the samples, correlate well in three of the longer cores, in good agreement with independent lithostratigraphic determinations. In addition, we have been able to detect local disconformities that appear as interruptions of the magnetic record. A continuous record of normal polarity has been found, extending from the present day to 13,000 14C vears BP. No reversals were recorded, though at two stratigraphic levels shallow inclinations, together with declination swings and low intensities of magnetization, may indicate rapid geomagnetic excursions. The magnetic record was attained at the time of deposition or shortly thereafter, and can be used for a wide range of applications.
Ice-Marginal Sedimentary, Glacitectonic, and Morphologic Features of Pleistocene Drift: An Example from Newfoundland
Authors: Eyles Nicholas , Slatt Roger M.
Published: December 2004

A Pleistocene drift sequence in hummocky terrain along part of the southern Avalon Peninsula of Newfoundland is interpreted to comprise complexly interrelated lodgement till, melt-out till, flow till, supraglacial and proglacial outwash, and supraglacial rhythmites. The gray and tan melt-out tills are stacked in imbricate fashion, giving rise to exceptionally thick stratigraphic sections. Contacts between melt-out tills are interpreted as remnants of shear planes because they are sharp, they dip in the up-ice direction, and they converge toward valley margins. Overlying flow tills interdigitate with supraglacial outwash. The drift sequence was deposited during a single episode of glaciation, rather than by repeated glacier advance, as previously proposed. It is the product of thrusting of englacial debris along ice-marginal shear planes, subsequent melting-out of englacial debris, and formation of supraglacial flow till and outwash. Preservation of this sequence probably is due to high content of englacial debris within the Wisconsinan ice. The sedimentary, glacitectonic, and morphologic features of this sequence are similar to those found at the margins of certain Arctic glaciers of subpolar thermal regime which have recently been the subject of Pleistocene glacial sedimentation models for west-central Canada and Great Britain. Recognition of these distinct elements indicates wisconsinan glacier lobes were of the cold Arctic type in southeastern Newfoundland. Alternative explanations for this sequence, such as deposition by glaciers of temperate thermal regime or by surging glaciers, are discounted. Because the features described here are complex and difficult to recognize, they may be more widespread in Pleistocene drift than has previously been interpreted.
Comparative 210Pb, 137Cs, and Pollen Geochronologies of Sediments from Lakes Ontario and Erie
Authors: Robbins J.A. , Edgington D.N. , Kemp A.L.W.
Published: December 2004

The distribution of 210Pb, 137Cs, and Ambrosia (ragweed) pollen in two sediment cores from Lake Ontario and in three cores from Lake Erie provides independent estimates of sediment accumulation rates. Geochronology with 210Pb is based on radioactive decay of the isotope following burial in sediments. The method can reveal with precision changes in sedimentation occurring over the past 100 yr or so. Geochronologies with 137Cs and Ambrosia are based on the occurrence of a horizon corresponding, respectively, to the onset of nuclear testing 25 yr ago and to regional forest clearance in the middle 1800s. These methods provide estimates of long-term average sediment accumulation rates. In all but one core, the distributions of 137Cs and 210Pb indicate no physical mixing of near-surface sediments. In two cores, including one from central Lake Erie collected by diver, all three estimates of sedimentation rates are in excellent agreement. In two other cores, rates based on 210Pb are significantly higher than those inferred from Ambrosia pollen profiles. Lower average rates appear to result from occasional massive losses of sediments. Such events, apparent in the distribution of 210Pb but not in pollen records, correlate with the occurrence of major storm surges on the lakes during this century. In one core from western Lake Erie, exponential distributions of both 210Pb and Ambrosia appear to be artifacts which may result from extensive biological or physical reworking of sediments in shallow water (11 m). Previous indications of increased sedimentation in Lake Erie since about 1935 based on Castanea (chestnut) pollen data are not substantiated.
A Possible Varving Mechanism for Meromictic Lakes
Authors: Dickman M. D.
Published: December 2004

A variety of mechanisms have been proposed to explain how light and dark couplets are formed in the profundal sediments of meromictic lakes but none of these explanations acknowledges the significance of the sudden and massive mortality of mixolimnetic anaerobic bacteria. Data collected from sedimentation chambers suspended below the chemocline in a small meromictic lake indicate that a massive mortality of photosynthetic bacteria was induced by a sudden intrusion of partially oxygenated water into the anaerobic lower mixolimnion. The resulting deposition of anaerobic bacteria (0.45 mg dry wt cm−2day−1) contributed 60% of the annual sediment influx during a 14-day period. It is postulated that the sudden sedimentation of the anaerobic bacteria inhabiting the lower mixolimnion of some meromictic lakes contributed to the formation of the dark-colored laminae in the sediments of these lakes.
The Last 30,000 Years of Faunal History within the Grand Canyon, Arizona
Authors: Mead Jim I.
Published: December 2004

The vertebrate fauna of the last 30,000 radiocarbon years in the Grand Canyon is reviewed. Faunas accompanied with 92 14C dates have been analyzed from nine cave sites (four systematically excavated) and 50 packrat middens. Reasonably precise chronological and environmental data of late Pleistocene and Holocene age were obtained through dung studies in Rampart, Muav, and Stanton's Caves; from the numerous packrat middens; and from a ringtail refuse deposit in Vulture Cave. The desert tortoise, 8 species of lizards, 12 species of snakes, 68 species of birds, and 33 species of mammals are identified. Extinct animals include the avian carrion feeder, Teratornis merriami, and the mammalian herbivores, Oreamnos harringtoni, Camelops cf. hesternus, Equus sp., and Nothrotheriops shastense. There is no apparent abrupt end to the late Pleistocene as observed in the Grand Canyon fossil faunal or floral record. Animal and plant taxa of the Grand Canyon responded individually to the changes in climate of the last 30,000 yr. Both animal and plant fossil assemblages indicate that a pre-full glacial, a full glacial, and a late glacial woodland community with many less dominant desert taxa were slowly replaced by a Holocene desert community. All woodland taxa were absent from the lower elevations of the Grand Canyon by 8500 yr B.P.
Geologic Evidence for Age of Deposits at Hueyatlaco Archeological Site, Valsequillo, Mexico
Authors: Steen-McIntyre Virginia , Fryxell Roald , Malde Harold E.
Published: December 2004

Direct tracing of beds during excavation in May 1973, confirmed that the artifact-bearing layers at Hueyatlaco underlie 10 m of fine-grained, water-laid deposits that constitute part of the wide-spread Valsequillo gravels. Dissection of these deposits by the adjacent Río Atoyac has reached a depth of 50 m. The stratigraphic section at Hueyatlaco includes four distinctive tephra units. The oldest one occupies a small channel in a series of cut-and-fill stream deposits that have yielded bifacial tools. It lies more than a meter above flat-lying, fine-grained beds from which edge-retouched tools have been recovered. The three other tephra units occur higher in the section.

Fission-track ages on zircon phenocrysts from two of the younger tephra layers (370,000 ± 200,000 and 600,000 ± 340,000 yr, 2σ) agree with concordant uranium-series dates for a camel pelvis that was found associated with bifacial tools at Hueyatlaco (245,000 ± 40,000 yr by230Th and > 180,000 yr by231Pa). These dates are compatible with the depth of burial and subsequent dissection of the Hueyatlaco deposits, as well as with the degree of hydration of volcanic glass shards and with the extent of etching of heavy-mineral phenocrysts from within the tephra layers.

These findings suggest to us that further search for archaeological remains in deposits as old as those at Hueyatlaco would be warranted.
Quaternary Sea-Level Events on Northern San Clemente Island, California
Authors: Muhs Daniel R.
Published: December 2004

Global sea-level changes are expressed in the coastal landforms and deposits of northern San Clemente Island. Stratigraphic, radiometric, amino acid, and pedologic dating techniques have allowed the development of a chronology of sea-level changes for about the last 500,000 yr. A uranium-series date on coral of about 127,000 yr for the 2nd terrace serves as a calibration point for amino acid age estimates of four other mapped terraces. Two of these terraces have age estimates of about 80,000–105,000 yr, another has an age estimate of about 127,000 yr, and the 5th terrace on the west side of the island is estimated to be about 415,000–575,000 yr old. These dates correlate reasonably well with marine terraces dated elsewhere and with stages of the oxygen-isotope record that are thought to represent high stands of the sea. Weakly cemented calcareous dune sands (eolianites) are moderately extensive on northern San Clemente Island and appear to represent low stands of the sea, since calcareous shelf sands were the most likely source. A radiocarbon date of about 22,000 yr suggests that the youngest eolianite was deposited during the last glacial maximum. An older eolianite is estimated to be about 140,000–195,000 yr old based on stratigraphic relations and degree of soil development. The suggested ages for the eolianites also correlate well with oxygen-isotope estimates of low sea levels.
A Quantitative Comparison of Soil Development in Four Climatic Regimes
Authors: Harden Jennifer W. , Taylor Emily M.
Published: December 2004

A new quantitative Soil Development Index based on field data has been applied to chronosequences formed under different climatic regimes. The four soil chronosequences, developed primarily on sandy deposits, have some numeric age control and are located in xeric-inland (Merced, Calif.), xeric-coastal (Ventura, Calif.), aridic (Las Cruces, N. Mex.), and udic (Susquehanna Valley, Pa.) soil-moisture regimes. To quantify field properties, points are assigned for developmental increases in soil properties in comparison to the parent material. Currently ten soil-field properties are quantified and normalized for each horizon in a given chronosequence, including two new properties for carbonate-rich soils in addition to the eight properties previously defined. When individual properties or the combined indexes are plotted as a function of numeric age, rates of soil development can be compared in different climates. The results demonstrate that (1) the Soil Development Index can be applied to very different soil types, (2) many field properties develop systematically in different climatic regimes, (3) certain properties appear to have similar rates of development in different climates, and (4) the Profile Index that combines different field properties increases significantly with age and appears to develop at similar rates in different climates. The Soil Development Index can serve as a preliminary guide to soil age where other age control is lacking and can be used to correlate deposits of different geographical and climatic regions.
Soil Development in Till of Various Ages in Northeastern Pennsylvania
Authors: Levine Elissa R. , Ciolkosz Edward J.
Published: December 2004

Eleven well-drained soils formed in till parent materials of varying ages in northeastern Pennsylvania were studied to determine changes in the soils with time. Four profiles (three Lackawanna and one Bath) were formed in Woodfordian till (15,000 yr B.P.), and two (Leck Kill) were formed in Altonian till (>28,000, <75,000 yr B.P.). The remaining five (Allenwood) were formed in pre-Wisconsinan till (>75,000 yr B.P.). In these soils, the extractable iron oxide, extractable aluminum oxide, and kaolinite contents increase with age, as do the total clay and fine/total clay ratio. With increasing age, the maximum accumulation of these constituents is found deeper in the profile. The extractable silicon oxide distribution is constant with depth, but it decreases in overall amount with time. Gibbsite is found only in small amounts in the A horizon of Altonian soils, but occurs throughout the profile of pre-Wisconsinan soils, although only in small amounts. In general, differences were found in these soils which separated them into three groups representing varying degrees of soil development. A regression equation was derived to predict the age of soils formed from the Altonian till based on a “clay accumulation index” value for soils of known Woodfordian and Holocene ages. The equation log Y = 1.80 + 0.992(logX) best fit the data, with an r2 value of 0.913. Using this equation, a mean age of 41,000 yr was calculated for the Altonian soils. This date was used to derive a second equation to predict ages for pre-Wisconsinan soils. The equation with the highest r2 value (0.934) was log Y = 1.81 + 0.998(logX). Dates for soils developed in the White Deer till and the Laurelton till of the pre-Wisconsinan stage were calculated to be 86,000 and 91,000 yr B.P., respectively. These dates fall within ages estimated for the Sangamon Interglaciation and thus would appear to be too young for pre-Sangamonian materials. The probable reason for the “too-young age” is that the C-horizon material of the pre-Wisconsinan soils was weathered and did not provide an accurate estimate of clay accumulation for the prediction equation.
Ice-Age Simulations with a Calving Ice-Sheet Model
Authors: Pollard David
Published: December 2004

Variations of ice-sheet volume during the Quaternary ice ages are simulated using a simple ice-sheet model for the Northern Hemisphere. The basic model predicts ice thickness and bedrock deformation in a north-south cross section, with a prescribed snow-budget distribution shifted uniformly in space to represent the orbital perturbations. An ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level. The model produces a large ∼ 100,000-yr response in fair agreement (correlation coefficient up to 0.8) with the δ18O deep-sea core records. To increase confidence in the results, several of the more uncertain model components are extended or replaced, using an alternative treatment of bedrock deformation, a more realistic ice-shelf model of ice calving, and a generalized parameterization for such features as the North Atlantic deglacial meltwater layer. Much the same ice-age simulations and agreement with the δ18O records, as with the original model, are still obtained. The model is run with different types of forcing to identify which aspect of the orbital forcing controls the phase of the 100,000-yr cycles. First, the model is shown to give a ∼ 100,000-yr response to nearly any kind of higher-frequency forcing. Although over the last 2-million yrs the model phase is mainly controlled by the precessional modulation due to eccentricity, over just the last 500,000 yr the observed phase can also be simulated with eccentricity held constant. A definite conclusion on the phase control of the real 100,000-yr cycles is prevented by uncertainty in the deep-sea core time scales before ∼600,000 yr B.P. The model is adapted to represent West Antarctica, and yields unforced internal oscillations with periods of about 50,000 yr.
Cation-Ratio Dating: A New Rock Varnish Age-Determination Technique
Authors: Dorn Ronald I.
Published: December 2004

Rock varnish coats many surfaces of geomorphic and archaeologic interest in arid lands. All varnish dating techniques are limited by the time lag between the exposure of a surface to subaerial processes and the onset of varnishing. They are valid only where manganese is not remobilized after deposition, for example, in most arid environments. The premise of a new age-determination method, cation-ratio dating, is that the ratio of the more mobile cations (e.g., K and Ca) to titanium in varnish decreases with time. Although there are many inherent assumptions and potential limitations, cation-ratio dating has been verified on relative age-sequences from a Death Valley debris cone, Negev Desert talus flatirons, and prehistoric lake levels at Searles Lake in California. Varnish cation ratios have been calibrated to independently dated surfaces in the Coso volcanic field and vicinity in California. Tentative absolute dates have been assigned to geomorphic surfaces in the Coso area. Cation ratios have been used to distinguish relative ages of archaeologic artifacts in southwestern North America and to demonstrate that varnish at the South Stoddard locality, Mojave Desert, did not form in 25 yr.
Geology and Paleoecology of a Mid-Wisconsin Peat from the Queen Charlotte Islands, British Columbia, Canada
Authors: Warner Barry G. , Clague John J. , Mathewes Rolf W.
Published: December 2004

A peat bed on east-central Graham Island of the Queen Charlotte Islands occurs within a nonglacial fluvial succession that is both overlain and underlain by glacial deposits. Radiocarbon dates of 27,500 ± 400 and 45,700 ± 970 yr B.P. at the top and base of the peat, respectively, indicate that it was deposited during the mid-Wisconsin nonglacial interval. The peat is the first documented mid-Wisconsin organic deposit in northern coastal areas of British Columbia. Three local pollen zones are represented. The lowest zone (PM-1) is restricted to sandy silt directly underlying the dated peat. Very high Cyperaceae and moderate Poaceae pollen percentages characterize zone PM-1, and a variety of other herbs are common, suggesting an open landscape rather than a forested one. The middle zone (PM-2) is characterized by abundant pollen ofPicea, Tsuga mertensiana, and Cyperaceae, and also contains pollen ofAbies, a genus now absent from the Queen Charlotte Islands. Graham Island probably had extensive forests at this time, but abundant pollen and macrofossils of Cyperaceae and emergent aquatics such asHippuris vulgaris, Veronica scutellata, Potentilla palustris, andMenyanthes trifoliataindicate that there also were open wetland areas. Zone PM-3 also contains abundant arboreal pollen. Large amounts ofSphagnumspores andSelaginella selaginoidesmegaspores indicate succession of the wetland area at the sample site to a peat bog. Paleoecological analysis of the data suggests that subalpine vegetation elements were depressed by at least 400 m, probably due to a cooler climate. Probable modern analogs in southeastern Alaska and the presence ofAbies(probablyA. amabilis) indicate that precipitation was higher on eastern Graham Island during the mid-Wisconsin than at present.
Paleoenvironmental Implications of the Quaternary Distribution of the Eastern Chipmunk (Tamias Striatus) in Central Texas
Authors: Graham Russell W.
Published: December 2004

Four Quaternary cave sites in central Texas demonstrate that the eastern chipmunk (Tamias striatus) ranged more than 600 km southwest of its modern distribution. Climatographs suggest that the late Pleistocene/early Holocene summer climates were either 7.5°C cooler and 120 mm moister than today or 300 mm moister, if temperature remained unchanged. The distribution of T. striatus also implies that mixed deciduous forest existed on the eastern Edwards Plateau at this time.
Radiocarbon Dates from the East China Sea and Their Geological Implications
Authors: Yijian Chen , Gui Peng , Wengiang Jiao
Published: December 2004

Radiocarbon analysis plays an important role in studying the Quaternary geologic history of the East China Sea. More than 20014C dates have been published in various Chinese publications. The continental shelf of the East China Sea is one of the few large continental shelves in the world. Many low-lying flats and deltaic plains lie along the coast making it a favorable site for sea-level studies. Radiocarbon data from Neolithic sites, chenier ramparts, peaty deposits, and submarine sediments converge to suggest that oscillations of sea level have occurred: they also suggest that the lowest glacial sea levels probably occurred between 22,000 and 19,000 yr B.P. Calculation of the volume of the Yangtze River Delta, together with14C dates, indicates that more than 89% of the solid particles carried by the river were deposited in the delta. Due to the sedimentary load, the crust beneath the delta has subsided isostatically and tilted seaward. Marine shells provide many acceptable14C dates, but because they are easily transported, most samples from the continental shelf cannot be directly related to the history of sea-level changes.
Late Holocene Vegetation Changes in Greenwater Valley, Mojave Desert, California
Authors: Cole Kenneth L. , Webb Robert H.
Published: December 2004

Small-scale late Holocene vegetation changes were determined from a series of 13 modern and fossil packrat middens collected from a site in the Greenwater Valley, northern Mojave Desert, California. Although the site is above the modern lower limit ofColeogyne ramosissima(black-brush), macrofossils of this shrub are only present in samples younger than 270 yr B.P. In order to measure changes more subtle than presence vs absence, macrofossil concentrations were quantified, and principal components and factor analyses were used to distinguish midden plant assemblages. Both the presence/absence data and the statistical analyses suggest a downward shift of 50 to 100 m forColeogyne(blackbrush) communities between 1435 and 1795 A.D.
Responses of Floods to Holocene Climatic Change in the Upper Mississippi Valley
Authors: Knox James C.
Published: December 2004

Dimensions of Holocene relict channels and sedimentological characteristics of point bars associated with these relict channels were used to reconstruct a Holocene history of long-term changes in magnitudes of 1.58-yr floods in Upper Mississippi Valley watersheds of southwestern Wisconsin. The reconstructed record of floods shows relatively large and persistent (nonrandom) departures from contemporary long-term average flood magnitudes. The flood history indicates climatic changes that are broadly similar to climatic changes indicated from fossil pollen in the same region. The Holocene floods ranged from about 10–15% larger to 20–30% smaller than contemporary floods of the same recurrence frequency. Large floods were characteristic between about 6000 – 4500 and 3000 – 2000 yr B.P., and during a brief interval after 1200 yr B.P. Small floods were common between about 8000 – 6500, 4500 – 3000, and 2000 – 1200 yr B.P. These fluvial responses were found to be closely associated with a long-term episodic mobility and storage of sediments in the Wisconsin watersheds. During periods of relatively large floods, relatively rapid lateral channel migration either reworked or removed extensive tracts of valley bottom alluvium. In contrast, during periods of relatively small floods, relatively slow lateral channel migration is apparent and the channel and floodplain system appear to have been relatively stable.
Charcoal Analysis for Paleoenvironmental Interpretation: A Chemical Assay
Authors: Winkler Marjorie Green
Published: December 2004

A nitric acid digestion and ignition technique developed to measure relative frequencies of charcoal in lake and bog sediments measures the weight of charcoal relative to the dry weight of the sample (percentage charcoal) and gives results comparable to counting of microscopic charcoal. Differences in the two techniques caused by changes in sediment type were found especially in postsettlement and late-glacial parts of cores. Charcoal values from sediments less than 100-yr old cannot be compared to older charcoal values unless wood charcoal and charcoal from fossil fuel burning are separated microscopically. Tests of this chemical assay on mixtures of known weights of charcoal, leaves, and sand give correlations between observed and expected values of 0.99 to 1.00.
Lake Tapps Tephra: An Early Pleistocene Stratigraphic Marker in the Puget Lowland, Washington
Authors: Westgate J. A. , Easterbrook D. J. , Naeser N. D. , Carson R. J.
Published: December 2004

The rhyolitic Lake Tapps tephra was deposited about 1.0 myr ago, shortly after culmination of the early phase of the Salmon Springs Glaciation in the Puget Lowland. It is contained within sediments that were deposited in ponds or lakes in front of the reteating glacier. An herb-dominated tundra existed in the southern Puget Lowland at that time. Lake Tapps tephra is most likely the product of an eruption that in part was phreatomagmatic. It forms an early Pleistocene stratigraphic marker across the southern sector of the Puget Lowland and provides a link between Puget lobe sediments of the Cordilleran Ice Sheet and sediments deposited by Olympic alpine glaciers.
Late Quaternary Vertical Displacement Rate Across the Fish Springs Fault, Owens Valley Fault Zone, California
Authors: Martel Stephen J. , Harrison T. Mark , Gillespie Alan R.
Published: December 2004

A cinder cone located 11 km south of Big Pine, California, is vertically displaced 78 ± 6 m by the Fish Springs fault of the Owens Valley fault zone. The surfaces of Tahoe-age and Tioga-age alluvial fans that overlie the cone are vertically displaced 31 ± 3 and 3.3 ± 0.3 m, respectively. Neither the cinder cone nor the Tioga-age fan appears to have been laterally offset. The cone is dated by the39Ar/40Ar method at 314,000 ± 36,000 yr B.P. (2σ), indicating an average late Quaternary vertical displacement rate of 0.25 ± 0.03 mm/yr (2σ). The age of the Tahoe glaciation is uncertain, but probably corresponds to the age of marine oxygen isotope stage 4 and/or 6 (65,000–75,000 and 128,000–195,000 yr, respectively). If the older fan were deposited during stage 4, then the average post-Tahoe vertical displacement rate probably was at least twice the pre-Tahoe late Quaternary rate. If the displacement rate has been constant during the last 314,000 yr, then the surface of the Tahoe-age fan is dated at 124,000 ± 19,000 yr B.P., and the bulk of the fan most likely would have been deposited during stage 6. Based on the displacement of the surface of the Tioga-age (10,600 – 26,000 yr) fan, the average Holocene displacement rate appears to have been slightly less than the average late Quaternary rate.
A Simple Model for the Interpretation of Magnetic Records in Lacustrine and Ocean Sediments
Authors: Hilton John
Published: December 2004

Many sources of magnetic minerals have been implicated as potential influences on the magnetic record of lake and ocean sediments. The “state-of-the-art” of our knowledge of these sources and their properties has been used to define a model which indicates those sedimentary environments where specific magnetic mineral sources may influence the magnetic record. Authigenically formed magnetic minerals are only likely to be found in estuaries and eutrophic lakes. Cosmic deposition, eolian deposition, and magnetic bacteria may be important in low-accumulation-rate deep-ocean sediments. Whereas catchment-derived material is only likely to be the sole source of the magnetic record in high-accumulation-rate, low-productivity lakes, fly ash is only likely to be a dominant source in very-low-accumulation-rate lake and ocean sediments.
Evidence for a Shallow Early or Middle Wisconsin-Age Lake in the Bonneville Basin, Utah
Authors: Oviatt Charles G. , McCoy William D. , Reider Richard G.
Published: December 2004

Relatively complete stratigraphic records of the Bonneville cycle and of at least one and probably two earlier lacustrine are exposed along the Bear River below Cutler Dam in northern Utah between altitudes of 1290 and 1365 m. In most exposures the unconformity between the Bonneville Alloformation and the underlying unit, herein named the Cutler Dam Alloformation, is marked by slight erosional relief and by a weakly to moderately developed buried soil, herein named the Fielding Geosol. In truncated profiles, the Fielding Geosol reaches a maximum of stage II carbonate morphology. Wood from near the base of the Cutler Dam Alloformation yielded a 14C date of >36,000 yr B.P. (Beta-9845). Alloisoleucine/isoleucine (aIle/Ile) ratios of Sphaerium shells from the Cutler Dam beds average 0.15 ± 0.01 in the total hydrolysate, which is significantly greater than the average for Sphaerium shells of Bonneville age elsewhere in the basin. Therefore, the Cutler Dam Alloformation is older than 36,000 yr B.P., but much younger than deposits of the Little Valley lake cycle (140,000 yr B.P.?) which bear shells having significantly higher aIle/Ile ratios. The Cutler Dam Alloformation along the Bear River may be broadly correlative with marine oxygen-isotope stages 4 or 3. Fine-grained, fossiliferous, marginal-lacustrine facies of the Cutler Dam Alloformation are exposed at altitudes near 1340 m, and are probably the highest exposures of sediments deposited in the early or middle Wisconsin lake in the Bonneville basin.
Late Quaternary Pollen Records from the Kobuk and Noatak River Drainages, Northwestern Alaska
Authors: Anderson Patricia M.
Published: December 2004

Pollen diagrams from Joe and Niliq Lakes date to ca. 28,000 and 14,000 yr B.P., respectively. Mesic shurb tundra grew near Joe Lake ca. 28,000 to 26,000 yr B.P. with localPopuluspopulations prior to ca. 27,000 yr B.P. Shrub communities decreased as climate changed with the onset of Itkillik II glaciation (25,000 to 11,500 yr B.P.), and graminoid-dominated tundra characterized vegetation ca. 18,500 to 13,500 yr B.P. Herb tundra was replaced by shrubBetulatundra near both sites ca. 13,500 yr B.P. with local expansion ofPopulusca. 11,000 to 10,000 yr B.P. andAlnusca. 9000 yr B.P. MixedPicea glauca/P. marianawoodland was established near Joe Lake ca. 6000 yr B.P. These pollen records when combined with others from northern Alaska and northwestern Canada indicate (1) mesic tundra was more common in northwestern Alaska than in northeastern Alaska or northwestern Canada during the Duvanny Yar glacial interval (25,000 to 14,000 yr B.P.); (2) with deglaciation, shrubBetulaexpanded rapidly in northwestern Alaska but slowly in areas farther east; (3) an early postglacial thermal maximum occurred in northwestern Alaska but had only limited effect on vegetation; and (4) pollen patterns in northern Alaska and northwestern Canada suggest regional differences in late Quaternary climates.
Late Quaternary Vegetation of Southern Isla Grande De Chiloé, Chile
Authors: Villagran Carolina
Published: December 2004

Late-glacial-Holocene forest history of southern Isla Chiloé (latitude 43°10′ S) was reconstructed on the basis of pollen analysis in three profiles (Laguna Soledad, Laguna Chaiguata, Puerto Carmen). Prior to 12,500 yr B.P. pollen records are dominated by plant taxa characteristic of open habitats (Zone I). From 12,500 yr B.P. to the present, tree species predominate in the pollen records (Zones II–V). Between 12,500 and 9500 yr B.P. ombrophyllous taxa (Nothofagus, Podocarpus nubigena. Myrtaceae,Fitzroya/Pilgerodendron, andDrimys) are frequent in all pollen diagrams, suggesting a wetter and colder climate than the present. Between 9000 and 5500 yr B.P. Valdivian forest elements, such asNothofagus dombeyitype,Weinmannia, andEucryphia/Caldcluvia, dominate, indicating a period of drier and warmer climate. From 5500 yr B.P. onward, the expansion of mixed North Patagonian-Subantarctic forest elements and the increased frequence ofTepualiasuggest increased rainfall and temperatures oscillating around the modern values.

The change from open to forest vegetation (ca. 12,500 yr B.P.) probably represents the most pronounced climatic change in the record and can be interpreted as the glacial-postglacial transition in the study area.
Statistical Analysis of Grain Size Distribution in Pleistocene Sediments from Lake Biwa, Japan
Authors: Kashiwaya Kenji , Yamamoto Atsuyuki , Fukuyama Kaoru
Published: December 2004

Time series of grain-size distributions from Pleistocene sediments deposited in Lake Biwa during the past 550 millennia show dominant periods of 40,000 and 20,000 yr that are very close to those predicted by the Milankovitch theory, as well as a period of about 70,000 yr not directly predicted by this theory. The 70,000-yr period is strongest, followed by the 20,000-yr period. The sequences also show that coarser particles were deposited, in general, during strong solar insolation, whereas finer particles were deposited during weak insolation.
Dissolution and Preservation of Antarctic Diatoms and the Effect on Sediment Thanatocoenoses
Authors: Shemesh A. , Burckle L. H. , Froelich P. N.
Published: December 2004

Comparison of Southern Ocean diatom populations from (i) surface ocean production, (ii) underlying Antarctic sediments, and (iii) laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in Southern Ocean sediments. Increasing dissolution causes relative depletions in N. kerguelensis (K), enrichments in T. lentiginosa (L), and slight enrichments in E. antarctica (A). This reflects the relative susceptibility to dissolution of the three species that dominate Antarctic sediments. We have devised a preservation index for the Southern Ocean based on the ratio K/(K + L) to estimate relative extents of dissolution and applied it to natural assemblages. Holocene Southern Ocean sediments display increasing opal preservation toward higher latitudes, but south of the Antarctic Polar Front preservation decreases in the order: well preserved = SE Indian > S. Atlantic ∼ SW Indian > SE Pacific = poorly preserved. Dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum (LGM) sediments of the Indian and Pacific sectors, but in the Atlantic, increased E. antarctica abundances at LGM must have resulted from an increase in surface ocean production of this species. Holocene and LGM diatoms in Atlantic and Pacific sector sediments are equally well preserved, but in the Indian sectors, Holocene sediments are better preserved than those of LGM age. Paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution.
A Review of Age Determinations on Pleistocene Corals in Eastern Australia
Authors: Pickett J.W. , Ku T.L. , Thompson C.H. , Roman D. , Kelley R.A. , Huang Y.P.
Published: December 2004

Samples of corals from all three previously reported Pleistocene localities in eastern Australia have been dated anew using the 230Th/234U technique. Results for two sites are confirmed, but the new results for the third site are older than previously reported and do not support a high sea level for isotope substage 5c. All sites are now referred to substage 5e.
Late Quaternary Vegetation and Climate of Southern Tierra del Fuego
Authors: Heusser Calvin J.
Published: December 2004

Vegetation and climate over approximately the past 13,000 yr are reconstructed from fossil pollen in a 9.4-m mire section at Caleta Róbalo on Beagle Channel, Isla Navarino (54°56′S, 67°38′W), southern Tierra del Fuego. Fifty surface samples reflecting modern pollen dispersal serve to interpret the record. Chronologically controlled by nine radiocarbon dates, fossil pollen assemblages are: Empetrum-Gramineae-Gunnera-Tubuliflorae (zone 3b, 13,000–11,850 yr B.P.), Gramineae-Empetrum-assorted minor taxa (zone 3a, 11,850-10,000 yr B.P.), Nothofagus-Gramineae-Tubuliflorae-Polypodiaceae (zone 2, 10,000–5000 yr B.P.), Nothofagus-Empetrum (zone 1b, 5000-3000 yr B.P.), and Empetrum-Nothofagus (zone 1a, 3000-0 yr B.P.). Assemblages show tundra under a cold, dry climate (zone 3), followed by open woodland (zone 2), as conditions became warmer and less dry, and later, with greater humidity and lower temperatures, by closed forest and the spread of mires (zone 1). Comparisons drawn with records from Antarctica, New Zealand, Tasmania, and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar Southern Hemisphere. The influences of continental and maritime antarctic air masses were apparently considerable in Tierra del Fuego during cold late-glacial time, whereas Holocene climate was largely regulated by interplay between maritime polar and maritime tropical air.
Seasonal Migration of Bison Antiquus from Rancho La Brea, California
Authors: Jefferson George T. , Goldin Judith L.
Published: December 2004

Evidence for annual seasonal migration of extinct Bison antiquus in the late Pleistocene fossil assemblage from Rancho La Brea, California, is demonstrated for the first time. The maturation of individuals from the B. antiquus sample was analyzed using the cheek tooth eruption sequence and occlusal wear patterns in juvenile and young adult inferior dentitions. Individual age of the specimens was established by comparison with wear stages observed in modern B. bison dentitions of known age. Assuming that reproductive behavior was restricted to a specific annual cycle similar to modern B. bison, B. antiquus was seasonally present at Rancho La Brea during the late spring. An annual migratory pattern is indicated by the presence in the assemblage of yearly groups of young individuals of the same age.
Radiocarbon Analyses from Cincinnati, Ohio, and Their Implications for Glacial Stratigraphic Interpretations
Authors: Lowell Thomas V. , Savage Kevin M. , Scott Brockman C. , Stuckenrath Robert
Published: December 2004

Detailed analysis of a site near Cincinnati, Ohio, shows that 14C ages of samples in a single geologic unit can have a range of several thousand years and ages from different stratigraphic units can overlap. At the Sharonville site, four 14C samples from organic silt below glaciogenic deposits have an inverted chronologic sequence, suggesting contamination, but nevertheless they indicate the silt was deposited before 27,000 yr B.P. A stump cluster in growth position, wood fragments, and moss from the upper surface of the silt may differ by as much as 2300 14C yr. Five ages from the stump cluster constrain the timing of a glacier advance of the Laurentide ice sheet to its southern limit in the Cincinnati area at 19,670 ± 68 yr B.P. Overlying glaciogenic sediments contain transported wood that may be as much as 3200 yr older than the advance. This range of ages points out that, for a given site, several age measurements are required to determine when a glacier advance occurred. Because the measured ages in this study span the entire interval suggested for a twofold sequence of advance, retreat, and readvance of the margin of the Miami sublobe, we suggest a single advance to its terminal position in the Cincinnati area as an alternate hypothesis for testing.
Volume and Routing of Late-Glacial Runoff from the Southern Laurentide Ice Sheet
Authors: Teller James T.
Published: December 2004

Melting of the Laurentide Ice Sheet during the last deglaciation added large volumes of water to many rivers and lakes of North America and to the world's oceans. The volume and routing of this meltwater not only helped shape the land's surface but also played a role in the evolution of late-glacial climate. A computerized model was prepared to quantify meltwater generation from seven drainage areas along the southern side of the Laurentide Ice Sheet at 500-yr time slices between 14,000 and 8000 yr B.P. Nearly all waters reaching the oceans flowed through the St. Lawrence, Hudson, or Mississippi River valleys. Discharge through the Mississippi River to the Gulf of Mexico during late-glacial time varied by more than a factor of 5, ranging between 17,400 m3 sec−1 (550 km3 yr−1) and 98,200 m3 sec−1 (3200 km3 yr−1). Discharge entering the North Atlantic Ocean through the St. Lawrence and Hudson valleys ranged between 20,300 m3 sec−1 (640 km3 yr−1) and 65,300 m3 sec−1 (2060 km3 yr−1), with very abrupt, twofold changes at about 11,000, 10,000, and 9500 yr B.P. as a result of the rerouting of water from the Lake Agassiz basin. As the areal extent and mass of the Laurentide Ice Sheet diminished, the total volume of meltwater plus runoff due to precipitation from its southern side declined from 3800 km3 yr−1 at about 14,000 yr B.P. to 2100 to 2600 km3 yr−1 between 11,500 and 8000 yr B.P. No meltwater entered the Gulf of Mexico after 9500 yr B.P. After the demise of the ice sheet over Hudson Bay about 8000 yr B.P., the modern continental drainage network was established and flows through the St. Lawrence declined to modern values of about 320 km3 yr−1.
Filtering of Milankovitch Cycles by Earth's Geography
Authors: Short David A. , Mengel John G. , Crowley Thomas J. , Hyde William T. , North Gerald R.
Published: December 2004

Earth's land-sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation. We examine this modification in the frequency domain by generating 800,000-yr time series of maximum summer temperature in selected regions with a linear, two-dimensional, seasonal energy balance climate model. Previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land. Although the observed response in the geologic record is sometimes significantly different than modeled here (differences attributable to model limitations and feedbacks involving the ocean-atmosphere-cryosphere system), there are several results of significance: (1) in mid-latitude land areas the orbital signal is translated linearly into a large (>10°C) seasonal temperature response; (2) although the modeled seasonal response to orbital forcing on Antarctica is 6°C, the annual mean temperature effect (<2°C) is only about one-fifth that inferred from the Vostok ice core, and primarily restricted to periods near 41,000 yr; (3) equatorial regions have the richest spectrum of temperature response, with a 3000-yr phase shift in the precession response, plus some power near periods of 10,000–12,000 yr, 41,000 yr, 100,000 yr, and 400,000 yr. Peaks at 10,000–12,000 yr and 100,000 and 400,000 yr result from the twice-yearly passage of the sun across the equator. The complex model response in equatorial regions has some resemblance to geologic time series from this region. The amplification of model response over equatorial land masses at the 100,000-yr period may explain some of the observed large variance in this band in geologic records, especially in pre-Pleistocene records from times of little or no global ice volume.
Stable Isotope Ratios of Carbon in Phytoliths as a Quantitative Method of Monitoring Vegetation and Climate Change
Authors: Kelly Eugene F. , Amundson Ronald G. , Marino Bruno D. , Deniro Michael J.
Published: December 2004

The13C/12C ratios of occluded carbon within opal phytoliths from the northern Great Plains show potential as a basis for paleoclimatic reconstruction. A significant correlation exists between the carbon isotopic composition of a host plant and that of the organic matter in its phytoliths. The13C/12C ratios for phytoliths from surface layers of soils along climatic gradients reflect the current proportions of C3and C4plants. Variations in the δ13C values of phytoliths with soil depth are caused by a variety of processes: burial of soil surface by dust, bioturbation, and possible illuviation by percolating water. Also, contributions of phytoliths by dust and roots have unknown isotopic effects. The δ13C values of phytoliths from soils increase with decreasing14C age, suggesting that the proportion of C4plants in this region has increased during the Holocene. Phytoliths of apparent mid-Holocene age suggest exclusive dominance by C4plants which agrees with paleoclimatic interpretations of an arid middle Holocene climate.
Stratigraphy and Chronology of Late Pleistocene Reefs in the Southern Cook Islands, South Pacific
Authors: Woodroffe Colin D. , Short Stephen A. , Stoddart David R. , Spencer Tom , Harmon Russell S.
Published: December 2004

The Makatea Islands in the southern Cook Islands consist of a degraded volcanic core surrounded by emergent “makatea” limestones. While much of this reefal limestone is of Tertiary age, the seawardmost reefs are late Pleistocene. Last-interglacial reefs (oxygen isotope substage 5e) identified by U-series dating reach 12.2 m on Atiu (mean age of three samples 126,000 ± 5000 yr B.P.), 9.8 m on Mitiaro (mean age of five samples 119,000 ± 3000 yr B.P.), 10.0–12.7 m on Mauke (mean age of four samples 128,000 + 5000, −4,000 yr B.P.), and 14.5–20.0 m on Mangaia (mean age of four samples 115,000 ± 7000 yr B.P.). On Atiu, Mauke, and Mitiaro a lower reef unit has been identified, and is separated from the overlying substage 5e reef by a sharp discontinuity, often with a crust of coralline algae. U-series dating from Atiu and Mauke indicates that this is a stage 7 reef formed in the penultimate interglaciation. The Makatea Islands have emerged as a result of flexure of the lithosphere in response to loading by the Pleistocene volcanic island of Rarotonga. Isolated outcrops of makatea limestone on Rarotonga reach 3.5 m and are probably of substage 5e age. Elastic and viscoelastic models of lithospheric flexure predict that much of the compensatory movement should occur shortly after the emplacement of the load. However, the age and elevation of late Quaternary reefs on the southern Cook Islands, where a Pleistocene volcanic island has loaded relatively old ocean floor (>80 myr), indicate that differential uplift has been continuing over the last 250,000 yr.