bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiocarbon Dates and Late-Quaternary Stratigraphy from Mamontova Gora, Unglaciated Central Yakutia, Siberia, U.S.S.R.
Authors: Péwé Troy L. , Journaux André , Stuckenrath Robert
Published: July 2006

A fine exposure of perennially frozen ice-rich silt and associated flora and vertebrate fauna of late-Quaternary age exists at Mamontova Gora along the Aldan River in central Yakutia, Siberia, U.S.S.R. The silt deposit caps a 50-m-high terrace and consists of three units. An upper layer 1–2 m thick overlies a 10–15-m-thick brownish to black silt layer. The lower silt layer is greenish to gray and about 15 m thick. All the silt is well sorted with 60% of the particles falling between 0.005 and 0.5 mm in diameter and is generally chemically and mineralogically homogeneous. The middle unit contains may extinct vertebrate mammal remains and ice wedges. The lower unit contains little vegetation and no ice wedges. The silt is widespread and exists as a loamy blanket on terraces at various elevations on both sides of the lower Aldan River. The origin of the silt blanket of late-Quaternary age in central Yakutia has long been controversial. Various hypotheses have been suggested, including lacustrine and alluvial, as well as frost-action origins. It is sometimes referred to as loess-like loam. Péwé believes the silt at Mamontova Gora is loess, some of which has been retransported very short distances by water. The silt probably was blown from wide, braided, unvegetated flood plains of rivers draining nearby glaciers. The silt deposits are late Quaternary in age and probably associated with the Maximum glaciation (Samarov) and Sartan and Syryan glaciations of Wisconsinan age. On the basis of biostratigraphy, 10 radiocarbon dates, and their relation to the nearby glacial record, it is felt that the upper unit at Mamontova Gora is Holocene and the middle unit is Wisconsinan. The youngest date available from the middle unit at this particular location is 26,000 years. Dates greater than 56,000 years were obtained in the lower part of the middle unit. The lower unit is definitely beyond the range of radiocarbon dating and probably is older than the last interglacial. The sediment, fauna, ice wedges, stratigraphy, and age of perennially frozen slit deposits in central Alaska are remarkably similar to those of the deposits exposed in central Yakutia. Both areas consist of unglaciated rolling lowlands and river terraces surrounded by high mountains that were extensively glaciated in Pleistocene time. The glaciers extended from the high mountains to the edges of the ranges. In both regions, extensively braided, silt-charged rivers drained the mountains and flowed through the lowlands on their way to the sea. It follows that there should be a similar late-Quaternary history.
Changing Patterns in the Holocene Pollen Record of Northeastern North America: A Mapped Summary
Authors: Bernabo J. Christopher , Webb Thompson
Published: July 2006

By mapping the data from 62 radiocarbon-dated pollen diagrams, this paper illustrates the Holocene history of four major vegetational regions in northeastern North America. Isopoll maps, difference maps, and isochrone maps are used in order to examine the changing patterns within the data set and to study broad-scale and long-term vegetational dynamics. Isopoll maps show the distributions of spruce (Picea), pine (Pinus), oak (Quercus), herb (nonarboreal pollen groups excluding Cyperaceae), and birch + maple + beech + hemlock (Betula, Acer, Fagus, Tsuga) pollen at specified times from 11,000 BP to present. Difference maps were constructed by subtracting successive isopoll maps and illustrate the changing patterns of pollen abundances from one time to the next. The isochrone maps portray the movement of ecotones and range limits by showing their positions at a sequence of times during the Holocene. After 11,000 BP, the broad region over which spruce pollen had dominated progressively shrank as the boreal forest zone was compressed between the retreating ice margin and the rapidly westward and northward expanding region where pine was the predominant pollen type. Simultaneously, the oak-pollen-dominated deciduous forest moved up from the south and the prairie expanded eastward. By 7000 BP, the prairie had attained its maximum eastward extent with the period of its most rapid expansion evident between 10,000 and 9000 BP. Many of the trends of the early Holocene were reversed after 7000 BP with the prairie retreating westward and the boreal and other zones edging southward. In the last 500 years, man's impact on the vegetation is clearly visible, especially in the greatly expanded region dominated by herb pollen. The large scale changes before 7000 BP probably reflect shifts in the macroclimatic patterns that were themselves being modified by the retreat and disintegration of the Laurentide ice sheet. Subsequent changes in the pollen and vegetation were less dramatic than those of the early Holocene.
The Fauna and Overall Interpretation of the “Cutting 10” Acheulean Site at Elandsfontein (Hopefield), Southwestern Cape Province, South Africa
Authors: Klein Richard G.
Published: July 2006

The Cutting 10 site at Elandsfontein (Hopefield), southwestern Cape Province, South Africa, is one of only three sites in southern Africa where bones and Acheulean artifacts have been documented together in primary or near primary context and the only such site where the association is in the open air. The Cutting 10 bones belong to a minimum of 15 mammalian species, which together suggest both a mid-Pleistocene age for the site and a vegetational setting in which grasses played a much more important role than they did historically. The absence of evidence for hearths, windbreaks, and other features, the composition of the artifact assemblage, the relatively sparse scatter of bones and artifacts, the relatively high bone to artifact ratio, the species composition of the fauna, and the numbers of different kinds of skeletal elements represented all indicate that the Cutting 10 occurrence was more a butchering site than a campsite. Although people are probably responsible for most of the bones, some of them probably come from animals that were killed by large carnivores or that died naturally.
Impact of Climatic Change on an Arid Watershed: Nahal Yael, Southern Israel
Authors: Bull William B. , Schick Asher P.
Published: July 2006

The Nahal Yael basin is underlain chiefly by schist, amphibolite, and granite. Thin (generally <1 m thick), grussy colluvium which covered the lower portions of granitic hillslopes in the late Pleistocene has now been stripped completely, causing marked contrasts in outcrop morphologies, even where there is no contrast of fracture density or petrologic characteristics. Formerly mantled slopes are now smooth and crumbly, and lack desert varnish. Previously unmantled slopes are rough and craggy, and varnished but little weathered. Such stripping suggests a change from a semiarid to a drier and/or warmer climate. Slopes underlain by amphibolite responded similarly to the climatic change, but the amphibolite was more deeply weathered, and the colluvium was only partially stripped. The least stripping of colluvium occurred on schist hillslopes, partly because schist outcrops require more rain to generate runoff, and partly because angular blocks of schist require larger flows for transport, compared to other slope lithologies. The stream subsystem responded to the climatically induced changes in the discharge of water and sediment from the hillslopes. Increase in sediment yield caused valley alluviation in the early Holocene, and a decrease in sediment yield later in the Holocene caused entrenchment of the valley fill. More granite and amphibolite gravel-size particles are transported now than when the hillslopes were extensively mantled. Dense networks of trails are not common on Holocene geomorphic surfaces, but are present on remnants of Pleistocene surfaces.
Etching of Hornblende Grains in Arctic Soils: An Indicator of Relative Age and Paleoclimate
Authors: Locke William W.
Published: July 2006

The degree of etching of hornblende grains in soils is defined as the mean depth of maximum etching on 100 grains per sample and is a function of: (1) the depth in the profile; (2) the age of the deposit on which the soil is formed; and (3) the climate since deposition. In soils formed on moraines in the eastern Canadian Arctic, etching decreases logarithmically with increasing depth in the profile, and the rate of etching at a given depth decreases logarithmically with increasing age. The most important climatic parameter with respect to etching appears to be the effective precipitation. Equally important in terms of soil moisture regimen is the presence of unfrozen water. Both affect the rate of etching as a function of depth and age. The inferred climate of northern Cumberland Peninsula, Baffin Island, N.W.T., Canada, preceding, during, and following the last (Foxe) glaciation, is indicated by the degree of etching of hornblende grains in soil profiles of various ages as follows: pre-Foxe—warm/wet; early to middle Foxe—mild/moist; middle to late Foxe—cold/arid; Hypsithermal—mild/moist; Neoglacial—cool/dry.
A Pollen Record from Birket Qarun and the Recent History of the Fayum, Egypt
Authors: Mehringer Peter J. , Petersen Kenneth L. , Hassan Fekri A.
Published: July 2006

Sediments and fossil pollen of two short cores from Birket Qarun, Egypt, reflect Nile floods, lake levels, and agricultural developments of the last 325 yr, and demonstrate the potential of a long and detailed record from the Fayum Depression. The chronology of these cores is inferred by correlation of historic events with changes in the fossil and sedimentary records.

Subangular clay clasts and blocky structure resulting from occasional exposure, drying, and reworking of lake sediments reflect low Nile floods of the mid-1600s. Abundant pollen of shallowwater, rooted aquatic plants provides evidence for continued low lake levels through the 1700s. A high lake level, resulting from the extreme Nile flood of 1817–1818, is recorded by hystrichospheres, reworked by wave action, from Eocene marine sediments exposed on the north shore of Birket Qarun.

Political administration, as reflected in agricultural policy, is also recorded in lake history. Changing lake levels are, in part, correlated with canal neglect during Mamluk and Ottoman control, and renewed canal maintenance under the agricultural policy of Mohammed Ali. Increased cattail (Typha) pollen dates from perenial irrigation after 1873. Olive and date pollen, and pollen of newly introduced exotic trees, are abundant after 1930 as a result of accelerated introduction and cultivation of fruit, lumber, fuel, and windbreak trees following World War I. The sequence of introduction of exotic plants is reflected in the pollen ofZea mays, from the New World, followed byCasuarinafrom Southeast Asia and Australia, andEucalyptusfrom Australia.
Late Wisconsin Vegetational and Climatic History at Kylen Lake, Northeastern Minnesota
Authors: Birks H. J. B.
Published: July 2006

Kylen Lake, located within the Toimi drumlin field, is critically positioned in relation to Late Wisconsin glacial advances, for it lies between the areas covered by the Superior and St. Louis glacial lobes between 12,000 and 16,000 yr B.P. The pollen and plant-macrofossil record suggests the presence of open species-rich “tundra barrens” from 13,600 to 15,850 yr B.P. Small changes in percentages ofArtemisiapollen between 14,300 and 13,600 yr B.P. appear to be artifacts of pollen-percentage data. Shrub-tundra with dwarf birch, willow, andRhododendron lapponicumdeveloped between 13,600 and 12,000 yr B.P. Black and white spruce and tamarack then expanded to form a vegetation not dissimilar to that of the modern forest-tundra ecotone of northern Canada. At 10,700 B.P. spruce and jack pine increased to form a mosaic dominated by jack pine and white spruce on dry sites and black spruce, tamarack, and deciduous trees such as elm and ash on moist fertile sites. At 9250 yr B.P. red pine and paper birch became dominant to form a vegetation that may have resembled the dry northern forests of Wisconsin today. The diagram terminates at 8410 ± 85 yr B.P. Climatic interpretation of this vegetational succession suggests a progressive increase in temperature since 14,300 yr B.P. This unidirectional trend in climate contrasts with the glacial history of the area. Hypotheses are presented to explain this lack of correspondence between pollen stratigraphy and glacial history. The preferred hypothesis is that the ice-margin fluctuations were controlled primarily by changes in winter snow accumulation in the source area of the glacier, whereas the vegetation and hence the pollen stratigraphy were controlled by climatic changes in front of the ice margin.
Recent Sediment Flux and Erosional Processes in a Welsh Upland Lake-Catchment Based on Magnetic Susceptibility Measurements
Authors: Dearing John A. , Elner Janet K. , Happey-Wood Christine M.
Published: July 2006

Single sample magnetic susceptibility measurements are used to correlate synchronous levels in 16 cores of dated (210Pb, 137Cs) recent sediment taken from the deep and oligotrophic Llyn Peris, N. Wales, in order to provide a basis for calculating total sediment and chemical influx through time. Results show that sediment influx has steadily increased since c. 1750 A.D. to reach peak levels in the period 1966–1976 A.D., equivalent to a rise in erosion in the catchment from c. 5 t km−2 yr−1 to c. 42 t km−2 yr−1. Comparison of down-core susceptibility fluctuations with sediment pollen and organic pigment data indicates that maximum susceptibility values relate to periods of channel erosion and minimum susceptibility values relate to periods of slate debris inwash from spoil tips in the catchment. A study of historical records reveals that pre-twentieth-century peak levels of erosion were due to the effects of extractive industries, while twentieth-century erosion has been caused by overgrazing, increased trampling pressure, and heavy construction works in the catchment.
Vegetation East of the Rocky Mountains 18,000 Years Ago
Authors: Wright H.E.
Published: July 2006

The various lobes and segments of the southern periphery of the Laurentide ice sheet reached their maximum extension at different times between 21,000 and 14,000 yr ago, but the CLIMAP date of 18,000 yr ago is taken as a reference level to review the distribution of major vegetational formations in central and eastern United States. Tundra was apparently confined to a narrow belt peripheral to the ice margin only in the Minnesota area and from northern Pennsylvania to New England, with extensions down the crest of the Appalachian Highlands at least as far as Maryland. Some areas south of the Great Lakes may later have been marked by treeless vegetation briefly as the ice retreated. The boreal forest to the south in the central United States was dominated by spruce; the jack pine that had prevailed during previous times was apparently eliminated by the time the ice reached its maximum. In the Appalachian Highlands and the Atlantic Coastal Plain, however, jack pine occurred along with spruce, which decreased in importance southward. The southern limit of the boreal forest in the Southeast was perhaps somewhere in southern Georgia and Alabama. Oak and other temperate deciduous trees were minor components of the boreal coniferous forests especially in the southern Appalacchians, but there is no evidence yet in the southeastern states for a relic mixed mesophytic forest 18,000 yr ago similar to the rich modern deciduous forests of the region, except possibly in the Lower Mississippi Valley. The climate in much of the Southeast was apparently dry as well as cool at that time; in Florida oak/pine scrub and prairie-like openings prevailed, and all but the deepest lakes dried up.
Pollen and Oxygen Isotope Analyses on Late- and Post-Glacial Sediments of the Tourbière de Chirens (Dauphiné, France)
Authors: Eicher U. , Siegenthaler U. , Wegmüller S.
Published: July 2006

The sequence of vegetation phases in the late Glacial was studied in a sediment section from the bog Tourbière de Chirens by means of pollen analysis.18O/16O ratios of samples of lacustrine marl, obtained from the same profile, reflect variations of18O/16O in precipitation and thus provide an additional, independent paleoclimatic record. The observed18O/16O variations agree well with the climatic history as deduced from pollen analysis. The climatic transition from the Oldest Dryas to the Bølling periodsensu lato, as well as the beginning and end of the Younger Dryas cold phase, is marked by abrupt changes in the18O/16O ratio which were observed also in other regions of the Alps. These drastic climatic changes probably took place simultaneously over large areas of Central Europe and occurred within short time spans.
The Sedimentary Framework of the Southern Basin of Lake George, New York
Authors: Hutchinson D.R. , Ferrebee W.M. , Knebel H.J. , Wold R.J. , Isachsen Y.W.
Published: July 2006

Information from 240 km of high-resolution seismic reflection profiles has been analyzed to show the bathymetric and subsurface configuration of southern Lake George in the southeastern corner of the Adirondack Mountains, New York. Three units have been identified and sampled in 13 piston cores as long as 7 m and 4 grab samples; they are glacial drift, glaciolacustrine nonorganic clay, and Holocene lake mud rich in organic material. Three deep bedrock basins controlled glacial, glaciolacustrine, and postglacial deposition within the lake. Glaciolacustrine clay is more than 30 m thick in these basins but is generally absent in water depths less than 20 m. An unconformity separates glaciolacustrine clay from overlying Holocene mud in water depths less than 30 m, but the contact is conformable and transitional in deeper water. The unconformity may have originated from subaqueous or subaerial erosion during a low stage of lake level which probably occurred between 10,000 and 700 yr B.P. Holocene lake mud is thin to absent in the shallower waters separating the three basins, but reaches 15-m thickness near the entrance to The Narrows. A new radiocarbon date of 6950 ± 60 yr B.P. was obtained from a wood fragment which was found in the Holocene lake mud. We found no clear evidence of postglacial tectonic disturbances of the lake sediments although recent releveling profiles suggest that the Adirondack Mountains are undergoing contemporary uplift.
Paleoclimatic Estimates from Water and Energy Budgets of East African Lakes
Authors: Hastenrath Stefan , Kutzbach John E.
Published: July 2006

The Turkana, Nakuru-Elmenteita, and Naivasha basins in the Rift Valley of East Africa experienced high water levels during the period of 10,000–7000 yr B.P. Analyses of the modern hydrologic and energy budgets for these basins, along with that of Lake Victoria, were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early Holocene. Precipitation must have been at least 150–300 mm/yr (15 to 35%) above the modern average. The precipitation estimates were fairly consistent among the various basins, but no quantitative estimate was made for the additional precipitation required to account for overflow from the Rift Valley lake basins. Discharge from the Lake Victoria basin around 1880 A.D. was considerably above the more recent average, and the increased discharge into the White Nile for that period might have been similar to that of the early Holocene. A sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic-energy budget; changes of albedo, Bowen ratio, and cloudiness were likely to have been of greater importance.
Age, Palaeoenvironments, and Climatic Significance of Late Pleistocene Konya Lake, Turkey
Authors: Roberts Neil
Published: July 2006

The Konya Basin, a closed depression at the southern margin of the Anatolian Plateau, contained a shallow but extensive lake during the late Quaternary. Nearshore sands and gravels containingDreissenashells form prominent depositional terraces around the basin edges at elevations between 1005 and 1020 m, and the highest has been dated at more than 30,000 yr B.P. The last major phase of limnic sedimentation occurred between 23,000 and 17,000 yr B.P., after which the lake fragmented into a number of subbasins or secondary depressions which evolved to become either marshes or playas. A final expansion of these residual lakes has been dated to ca. 11,000 yr B.P. in one secondary depression. Archaeological and other evidence indicate that only minor lake-level fluctuations occurred during the Holocene. The dominant sedimentary process over the last 10,000 years has been alluviation at the basin margin. The Konya sequence confirms that the most recent period of high-lake levels in the northern Near East was of the last glacial age. The palaeolakes of Anatolia and Iran were, however, more a product of reduced evaporation brought about by temperature depression than of changes in precipitation, and thus belie their often-used description as an indicator of “pluvial” climatic conditions.
Toward a Comprehensive Upper Quaternary Tephra and Ignimbrite Stratigraphy in New Zealand using Electron Microprobe Analysis of Glass Shards
Authors: Froggatt P. C.
Published: July 2006

New Zealand Quaternary marine and terrestrial sequences contain numerous tephras, or volcanic-ash horizons, that are the distal correlatives of voluminous welded ignimbrite sheets, erupted from central North Island. Electron microprobe analyses of glass shards from the distal tephras demonstrate their homogeneity and are shown to identify each tephra examined. By matching tephras from stratigraphically controlled sequences, the first comprehensive tephra stratigraphy spanning from 50,000 to 700,000 yr ago and covering the New Zealand region is advanced.

Analyses on glass shards from the unwelded base of ignimbrite sheets are comparable to the distal tephra analyses and allow correlation between ignimbrites and to the distal tephras. The better exposed tephra record constrains the number of separate eruptive events and the stratigraphy of the ignimbrites, both of which were previously confused by lack of outcrop.

Samples from pumiceous marine sediments were found to contain two or more chemically distinct populations of glass. The pumice is in cross-bedded sands or sand lenses within conglomerate, attesting to a shallow high-energy environment where reworking could occur. However, each glass population could be matched to older, known tephras.
Late Wisconsin Macrofossil Records of Desert Vegetation in the American Southwest
Authors: Spaulding W. Geoffrey
Published: July 2006

Until recently, the oldest-known packrat (Neotoma spp.) midden records of desert scrub vegetation were less than 10,500 yr old and were restricted to altitudes below 300 m in the northern Sonoran Desert. Recent discovery of macrofossil assemblages in the Mojave Desert extends the record of desert vegetation back to 14,800 yr ago and to altitudes as high as 910 m. Although xerophytic conifer woodland was widespread in current desert habitats during the Late Wisconsin and early Holocene, the development of extensive desert vegetation was not delayed until the beginning of the middle Holocene. A regional vegetation mosaic of desert scrub and woodland existed at altitudes below 1000 m in the Mojave Desert during the last part of the Late Wisconsin.
Late-Quaternary Vegetational Dynamics and Community Stability Reconsidered
Authors: Delcourt Paul A. , Delcourt Hazel R.
Published: July 2006

Defining the spatial and temporal limits of vegetational processes such as migration and invasion of established communities is a prerequisite to evaluating the degree of stability in plant communities through the late Quaternary. The interpretation of changes in boundaries of major vegetation types over the past 20,000 yr offers a complementary view to that provided by migration maps for particular plant taxa. North of approximately 43°N in eastern North America, continual vegetational disequilibrium has resulted from climatic change, soil development, and species migrations during postglacial times. Between 33° and 39°N, stable full-glacial vegetation was replaced by a relatively unstable vegetation during late-glacial climatic amelioration; stable interglacial vegetation developed there after about 9000 yr B.P. Late-Quaternary vegetation has been in dynamic equilibrium, with a relatively constant flora, south of 33°N on upland interfluves along the northern Gulf Coastal Plain, peninsular Florida, and west-central Mexico.
Age and Paleoclimatic Implications of the Bet Shean Travertines
Authors: Kronfeld J. , Vogel J. C. , Rosenthal E. , Weinstein-Evron M.
Published: July 2006

From 41,000 to over 22,000 yr B.P., a massive and areally extensive spring travertine was deposited in the Bet Shean Valley, Israel. This travertine is coeval with the Ami'az Member of the Lisan Formation which represents a high lake stand. The travertine deposition is contemporaneous with a more active hydrologic regime associated with wetter conditions in the arid zones of the southern Levant adjacent to southern Israel. These wetter conditions facilitated formation of a widespread spring tufa and also enhanced the water levels of Lake Lisan.
Expansion of Magellanic Moorland during the Late Pleistocene: Palynological Evidence from Northern Isla de Chiloé, Chile
Authors: Villagrán Carolina
Published: July 2006

The late Quaternary vegetation of northern Isla de Chiloé is inferred from palynological analysis of a section in the Río Negro drainage (42°03′S, 73°50′W). At ca. 30,500 yr B.P., maxima ofAsteliaandDonatiaoccurred, suggesting wetland development. From that time until ca. 27,000 yr B.P., steppe indicators such as Compositae/Gramineae dominated, suggesting drier conditions. After 27,000 yr B.P., the moorland shrubDacrydiumgradually increased, reaching a maximum by 18,000 yr B.P. At this timeAsteliaincreased again, suggesting development of cushion bog during cold and wet conditions. The glacial-postglacial transition is characterized by a marked change from peaty sediments to clays, a decrease in the cushion bog flora, and the prevalence of Gramineae/ Compositae and swamp taxa. This vegetation prevailed until ca.7000 yr B.P. when forest taxa became dominant. The floristic pattern inferred from the pollen spectra of the Rio Negro section suggests that the late Pleistocene vegetation of Chiloé resembled modern Magellanic Moorland vegetation (52°–56°lat S). Based on climatic conditions presently associated with Magellanic Moorland, its occurrence in Chiloé at low elevations during the late Pleistocene implies a decrease in average temperature of at least 4°C and an increase in annual precipitation of at least 1500 mm.
Steppe Expansion in Patagonia?
Authors: Veblen Thomas T. , Markgraf Vera
Published: July 2006

Westward expansion of the Patagonian steppe and retrocession of Andean forests due to increasing aridity over the past one or two millennia has been a persistent theme in the ecological and paleoecological literature for at least half a century. New evidence from pollen profiles, tree-ring analysis, vegetation structure, and photographic and documentary historical sources does not show the expansion of the steppe. Instead, over the past century trees have invaded the steppe as a consequence mainly of human-induced changes in the fire regime, and trees have regenerated in forest areas that were heavily burnt at the onset of European colonization.
Palynologic and Geomorphic Evidence for Environmental Change During the Pleistocene-Holocene Transition at Point Reyes Peninsula, Central Coastal California
Authors: Rypins Steven , Reneau Steven L. , Byrne Roger , Montgomery David R.
Published: July 2006

Three sites on the Point Reyes Peninsula, California, provide evidence of major environmental change during the Pleistocene-Holocene transition. A 12,300-yr-long pollen record from Coast Trail Pond reveals a change from closed canopyPseudotsuga-Abiesforest to coastal scrub and grassland about 10,000 yr B.P. The same change is also evident in pollen records from two sea cliff exposures that contain a series of buried soils interstratified with fluvial and debris-flow deposits. Eight radiocarbon dates from these exposures indicate that aggradation at both sites began ca. 12,000 yr B.P. and that the change from forest to scrub and grassland occurred between 10,300 and 9400 yr B.P. High percentages of alder pollen and bracken fern spores reflect repeated geomorphic disturbance at ca. 10,400 yr B.P. The occurrence of major aggradation accompanied by recurrent debris flows between ca. 12,000 and 10,000 yr B.P. suggests that this was a period of more frequent high-intensity storms.
A Multivariate Mixing Model for Identifying Sediment Source from Magnetic Measurements
Authors: Yu Lizhong , Oldfield Frank
Published: July 2006

A sequential method for quantitative identification of sediment source components, based on magnetic measurements, has been developed and tested for sediments from the Rhode River, Maryland. Simulated mixing tests and multiple regression were employed to establish numerical relationships between source component proportions and the magnetic measurements of mixtures. On the basis of these multivariate mixing models, source components of three estuarine sediment cores were estimated by linear programming. The results strongly support the previous studies on this catchment which indicated a dramatic change in sediment source some 150 to 200 yr ago. Quantitative calculations are more useful and informative than purely qualitative descriptions.
500,000-Year Paleomagnetic Record from New Zealand Loess
Authors: Pillans Brad , Wright Ian
Published: July 2006

A paleomagnetic record of secular variation has been obtained from a 17.4-m-long core drilled from loess in North Island, New Zealand. Three dated rhyolitic tephra occur in the loess core at depths of 1.5, 3.4,and 13.0 m, with ages of 22,500, ≧42,000, and 370,000 years, respectively. The base of the core is estimated to be 500,000 years old, which makes this the longest continuous loess sequence yet described from the Southern Hemisphere. Two periods of anomalously low inclination in the core are correlated with the Mungo Event (ca. 35,000 years ago) and the Emperor Event (ca. 490,000 years ago); the Blake Event (ca. 115,000 years ago) is not recorded.
Discriminating Texturally Similar Tills in Central Minnesota by Graphical and Multivariate Techniques
Authors: Mooers Howard D.
Published: July 2006

The sequence of glaciation in the midwestern United States has been defined mainly by till stratigraphy. Correlation of tills over long distances, however, is complicated by spatial variation of sediment characteristics. In east-central Minnesota three till units were previously defined. Two were considered to be lithologically identical and were correlated with the late Wisconsin advance of the Rainy lobe, whereas a third till was assigned to the contemporaneous advance of the Superior lobe. This interpretation was inconsistent with subsequent glaciological reconstructions of the Rainy and Superior lobes. In an effort to define the parent lobe of the deposits in central Minnesota, the tills were sampled, analyzed, and compared by graphical and multivariate techniques. Graphical comparisons of sedimentological parameters were inadequate to distinguish important differences among the groups. However, principal component analysis of the analytical data indicates that the original interpretation is untenable and that one of the tills formerly assigned to the Rainlylobe should now be attributed to the Superior lobe. Problems encountered with correlation of tills exposed at the surface illustrate the complexity and problems associated with subsurface stratigraphic correlation.
Rainfall in the Negev Desert during the Middle Holocene, Based on13C of Organic Matter in Land Snail Shells
Authors: Goodfriend Glenn A.
Published: July 2006

Analysis of stable carbon isotope ratios (13C/12C) of organic matter in land snail shells is used to infer middle Holocene rainfall amounts in the Negev Desert by reconstructing the distribution of C4plants in the family Chenopodiaceae. The organics are derived from the diet of the snails, which consists of plant material, and are enriched in13C where C4plants are present. A survey of modern plant communities indicates that in areas receiving ≥300 mm mean annual rainfall, nearly all plant communities consist of C3species only (no C4chenopodes), whereas in areas under ≤230 mm rainfall, most plant communities contain one or more C4chenopode species. In between is a transition zone consisting of a mosaic of both pure C3and mixed C3+ C4plant communities. Isotopic results for fossil land snails indicate a consistent geographic pattern throughout the middle Holocene, from ca. 6500 to 3000 yr B.P., with the transition zone located ca. 20 km south of its present position. This implies a near doubling of rainfall within this region as compared to present.
Late Deglaciation of the Central Labrador Coast and Its Implications for the Age of Glacial Lakes Naskaupi and McLean and for Prehistory
Authors: Clark Peter U. , Fitzhugh William W.
Published: July 2006

The age of the marine limit and associated deglaciation has been estimated from relative sea-level curves for the Hopedale and Nain areas of the central Labrador coast as approximately 7600 ± 200 and 8500 ± 200 yr ago, respectively. These ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated. Because the central coast is due east of glacial lakes Naskaupi and McLean, the earliest the lakes could have formed was <8500 ± 200 yr ago, with their largest phases being fully established only after 7600 ± 200 yr ago. This suggests that the age of the lakes, and associated deglaciation of the central Labrador-Ungava region, is younger by at least 1500 yr than previously estimated. A late-glacial marine-based ice mass in Ungava Bay that dammed the lakes collapsed ca. 7000 yr ago. Within this time frame, therefore, the glacial lakes only existed for <500 yr. The persistence of the Laurentide Ice Sheet margin on the central Labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern Labrador.
Paleoclimatic implications of late quaternary lacustrine sediments in Western Nubia, Sudan
Authors: Pachur Hans-Joachim , Hoelzmann Philipp
Published: July 2006

Owing to the hypercontinental location of Western Nubia, secular fluctuations of climate have been filtered and wet phases can be considered as representative of conditions throughout the southeastern Sahara. The study area is crossed by the 20-mm isohyet; between 9300 and about 4000 yr B.P., however, there were widespread lake and swamp environments with freshwater molluscs, ostracods, and diatoms, and a species-rich savanna mammal fauna. The center of the West Nubian Basin (approx. 18°N), an area of about 20,000 km2, was occupied by a semiaquatic landscape which was situated at the same latitude as Paleolake Chad. From extensive lake carbonates up to about 4 m thick, a long-term rise of the groudwater table is inferred. Environments developed that now exist at about latitude 13°N. Radiocarbon dates from lake sediment sequences cluster between 30,000 and 21,000 yr B.P., indicating a Pleistocene wet phase. A gap in radiocarbon dates between 21,000 and 11,000 yr B.P. signals a phase of hyperaridity, similar to the present hyperarid phase, with eolian deflation and deposits of sand being the dominant forms of erosion and accumulation.
Comparative Uranium-Thorium and Thermoluminescence Dating of Weathered Quaternary Alluvium in the Tropics of Northern Australia
Authors: Nanson Gerald C. , Price David M. , Short Stephen A. , Young Robert W. , Jones Brian G.
Published: July 2006

Thermoluminescence (TL) age determinations of alluvial sediments in the tropics are evaluated by comparison with U/Th age determinations of pedogenic accumulations in the alluvium of the lower Gilbert River, a large fan delta in the wet-dry tropics of northern Queensland, Australia. This study extends U/Th dating by applying it not only to calcretes, but also to Fe/Mn oxyhydroxide/oxide accumulations. While a direct correlation cannot be made between U/Th dates from secondary minerals and TL dates from the host sediments, both sets of data show broad consistency. In addition to providing a minima for acceptable TL ages, U/Th dates are useful for determining the chronology of pedogenesis/diagenesis. They show that calcretes and ferricretes have formed under similar climatic conditions in the wet-dry tropics of northern Australia during the late pleistocene. Beneath about 5–12 m the Gilbert fan delta consists of an extensive sand body older than 85,000 yr and probably about 120,000 yr in age, representative of a period of major fluvial activity not repeated since this time. Above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that TL dates at 40,000–50,000 yr B.P. A system of sandy distributary channels over the fan surface represents an early Holocene fluvial phase probably more active than at present.
Holocene Trends in 18O in Land Snail Shells from the Negev Desert and Their Implications for Changes in Rainfall Source Areas
Authors: Goodfriend Glenn A.
Published: July 2006

The δ18O value of the carbonate of land snail shells is related to the 18O content of precipitation, which in turn relates to the source region and trajectory of the rain-bearing air masses. Analyses of 18O of the shell carbonate of 76 radiocarbon-dated Holocene samples of the land snail Trochoidea seetzeni from the northern Negev Desert in southern Israel were carried out and the results were compared to modern snails from the same region. Early Holocene δ18O values are similar to modern but during the period centered around 6500-6000 yr B.P., a depletion of some 2%. below modern is observed. A change in the atmospheric circulation pattern for this period is thus indicated, most likely an increase in the frequency of storm systems reaching the region from north-eastern Africa. By 3500 yr B.P., δ18O values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time.
A Middle Holocene Vegetation Record from the Mojave Desert of North America and its Paleoclimatic Significance
Authors: Spaulding W. Geoffrey
Published: July 2006

Packrat middens from the McCullough Range, in the southeastern Mojave Desert of Nevada, record vegetation conditions during the periods 6800 to 5060 yr B.P. and 1250 yr B.P. to present. Their age and location are ideal to test for middle Holocene aridity; the period between 6800 and 5060 yr B.P. does appear to have been more arid than during the late Holocene period of record. This agrees with other evidence for middle Holocene aridity from the Southwest. Arguments for strengthened middle Holocene monsoons in the region are based chiefly on packrat midden samples older than 7500 yr B.P., or on samples that are younger than 5500 yr B.P. Simulations of 6000 yr B.P. climate that fail to show strong subtropical flow into the Southwest are therefore supported by evidence for enhanced aridity in that region.
Response of the Columbia River Fluvial System to Holocene Climatic Change
Authors: Chatters James C. , Hoover Karin A.
Published: July 2006

An understanding of the response of a fluvial system to past climatic changes is useful for predicting its response to future shifts in temperature and precipitation. To determine the response of the Columbia River system to previous climatic conditions and transitions, a well-dated sequence of floodplain development in the Wells Reservoir region was compared with the paleoenvironmental history of the Columbia River Basin. Results of this comparison indicate that aggradation episodes, occurring approximately 9000-8000, 7000-6500, 4400-3900, and 2400-1800 yr B.P., coincided with climatic transitions that share certain characteristics. The inferred climates associated with aggradation had at least moderate rates of precipitation that occurred mainly in winter coupled with moderate winter temperatures. Such conditions would have resulted in the buildup of snowpacks and a high frequency of rain-on-snow events. The warming and precipitation increases predicted for the Pacific Northwest under most CO2-doubling scenarios are likely to repeat these conditions, which could increase the frequency of severe, sediment-laden floods in the Columbia River Basin.
New Discoveries at the Middle Pleistocene Acheulian Site of Gesher Benot Ya'aqov, Israel
Authors: Goren-Inbar N. , Belitzky S. , Verosub K. , Werker E. , Kislev M. , Heimann A. , Carmi I. , Rosenfield A.
Published: July 2006

The Gesher Benot Ya'aqov archaeological site in the northern Dead Sea Rift of Israel contains Acheulian artifacts and middle Pleistocene fossils. Initial results of a new interdisciplinary study have shown that fluviolacustrine sediments of the Benot Ya'aqov Formation, which contains several archaeological occupations, were deposited in an embayment of the Hula Basin. They were subsequently deformed by tectonic activity associated with the Dead Sea Rift. Biostratigraphy, magnetostratigraphy, and K-Ar dating serve to constrain the age of the Benot Ya'aqov Formation to between 240,000 and 730,000 yr B.P. Archaeological excavation of three areas and two trenches at the new study area have produced abundant basalt, flint, and limestone artifacts, mammalian and avian fossils, and considerable plant material. The lithic materials provide an excellent opportunity to study large assemblages of in situ Acheulian artifacts, a rare phenomenon in the middle Pleistocene Levantine record. In addition, the organic materials will facilitate paleoenvironmental reconstructions from an ecological-floral perspective.
Convergence and Divergence in ‘New Governance’ Arrangements: Evidence from European Integrated Natural Resource Strategies
Authors: HOWLETT MICHAEL , RAYNER JEREMY
Published: July 2006

To analyse convergence and divergence in Natural Resource New Governance Arrangements (NRNGAs) two regimes in the environmentally-related areas of forest and fisheries management are examined. The findings reveal limited convergence across sectors and countries in the general aims and ideas behind NGAs and evidence of significant policy divergence in the tools and mechanisms created for their implementation. The reasons for the differences lie primarily in the policy formulation process. While the impetus for the adoption of both NRNGAs is in the international and regional realms, without the force of either international law or competitive advantage, pressure for convergence is weak. Aspects of the policy formulation process, especially the manner in which the changing capacities of domestic public and private actors active in the affected resource policy arena interact to influence policy design, are critical for explaining policy convergence and divergence. Specifically, the interplay between the effect of the internationalization of resource policy issues, tending to increase private capacities at the expense of the public one, and the declining importance of primary industries, which has the reverse effect, is shown to have played an important role in NRNGA policy dynamics.
Werbung im Fernsehen
Authors: Nieding Gerhild , Ohler Peter , Bodeck Sabine , Werchan Anne
Published: July 2006

Zusammenfassung. In zwei Experimenten wurde der Frage nachgegangen, wie Kinder die Fähigkeit entwickeln, zwischen Werbung und anderen Programmformaten zu unterscheiden. In der Forschungsliteratur sind bislang im Besonderen zwei Fragen ungeklärt: (1) Ab welchem Alter können Kinder Werbung von Kinderfilmgenres diskriminieren, wenn keine singulären salienten Merkmale für Werbung vorliegen? (2) Ab wann wird das Konzept ‘Werbung‘ spontan zur Klassifikation von Programmformaten benutzt? Zur Beantwortung von Frage 1 wurden in einem Experiment mit 5- und 8-jährigen Kindern kurze Ausschnitte von Werbeclips und Kinderfilmen dargeboten. Die Kinder sollten schnellstmöglich mittels Tastendruck zwischen den beiden Programmformaten unterscheiden. Bereits die 5-Jährigen wiesen unter dieser Bedingung überzufällig hohe Trefferquoten auf. Zur Klärung von Frage 2 wurden in einem weiteren Experiment 4-, 6- und 9-Jährige mit einem Oddity-Problem konfrontiert, das eine Konzeptüberprüfung ohne Induktion der zugrundeliegenden konzeptuellen Kategorien zulässt. Dargeboten wurde ein Werbeclip zusammen mit zwei Kinderfilmen oder ein Kinderfilm zusammen mit zwei Werbeclips. Die Kinder erhielten eine explizite Oddity-Instruktion (“Eines davon ist anders“). Bereits die 4-jährigen Kinder waren dazu in der Lage, das Konzept ‘Werbung‘ über dem Zufallsniveau anzuwenden.
Influence of coarse lag formation on the mechanics of sediment pulse dispersion in a mountain stream, Squire Creek, North Cascades, Washington, United States
Authors: Brummer Chris J. , Montgomery David R.
Published: July 2006

Mountain channels closely coupled to landslide‐prone hillslopes often exhibit bed surface grain sizes coarser than transportable by annual high flows. Coarse particles within poorly sorted sediment delivered to channels by mass‐wasting processes may not be readily transported as bed load and can consequently form lag deposits that influence the morphology, hydraulic roughness, and sediment storage within mountain channel networks. A tracer study and comparison of supply and bed grain size distributions from a valley‐spanning landslide in the North Cascades of Washington state were used to derive relations between shear stress and the probability of particle entrainment and erosion from the sediment pulse. Rapid bed surface armoring formed a relatively immobile lag deposit within 2 years. Covering of 20% of the bed by lag boulders with <5% probability of entrainment was sufficient to retard vertical incision and force considerable channel widening during a flood with an 8‐ to 152‐year recurrence discharge on locally gauged streams. Our results imply that numerical models of sediment pulse evolution that do not explicitly incorporate the influence of lag formation may substantially overestimate long‐term dispersion rates. The grain size distribution and lithology of a sediment input relative to the flow competence of the receiving channel are important factors influencing the rates and mechanisms of sediment pulse dispersion and the sediment capacitance provided by coarse‐grained sediment pulses in mountain drainage basins.
Effect of interplanetary shock strengths and orientations on storm sudden commencement rise times
Authors: Wang C. , Li C. X. , Huang Z. H. , Richardson J. D.
Published: July 2006

We make a statistical survey of interplanetary (IP) shocks and storm sudden commencements (SSCs) observed between 1995 and 2004. We find that 75% of SSCs are associated with shocks, consistent with previous work. We use this survey to investigate the effect of the interplanetary shock strength and orientation on the SSC rise time. We find that the higher the speed of an IP shock, the less time it takes to sweep by the magnetosphere, and thus the shorter the rise time of the corresponding SSC. The orientation of an IP shock also effects the SSC rise time. Generally speaking, a highly oblique shock causes asymmetric compression of the magnetosphere with respect to the noon‐midnight meridian, takes more time to sweep by magnetosphere, and thus results in a longer rise time of the SSC.