bluuebunny/crossref_metadata_2025 huggingface dataset:
Palynology of Cushion Bogs of the Cordillera Pelada, Province of Valdivia, Chile
Authors: Heusser Calvin J.
Published: December 2004

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

New K–Ar ages for a basalt flow interbedded with Tahoe and Tioga tills in Sawmill Canyon, southeastern Sierra Nevada, slightly refine previously published ages for the flow and provide an estimate of 53,000 ± 44,000 yr for the Tahoe-Tioga interglaciation.
Reinterpretation of the Exposed Record of the Last two Cycles of Lake Bonneville, Western United States
Authors: Scott William E. , McCoy William D. , Shroba Ralph R. , Rubin Meyer
Published: December 2004

A substantially modified history of the last two cycles of Lake Bonneville is proposed. The Bonneville lake cycle began prior to 26,000 yr B.P.; the lake reached the Bonneville shoreline about 16,000 yr B.P. Poor dating control limits our knowledge of the timing of subsequent events. Lake level was maintained at the Bonneville shoreline until about 15,000 yr B.P., or somewhat later, when catastrophic downcutting of the outlet caused a rapid drop of 100 m. The Provo shoreline was formed as rates of isostatic uplift due to this unloading slowed. By 13,000 yr B.P., the lake had fallen below the Provo level and reached one close to that of Great Salt Lake by 11,000 yr B.P. Deposits of the Little Valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods. The maximum level of the Little Valley lake was well below the Bonneville shoreline. Based on degree of soil development and other evidence, the Little Valley lake cycle may be equivalent in age to marine oxygenisotope stage 6. The proposed lake history has climatic implications for the region. First, because the fluctuations of Lake Bonneville and Lake Lahontan during the last cycle of each were apparently out of phase, there may have been significant local differences in the timing and character of late Pleistocene climate changes in the Great Basin. Second, although the Bonneville and Little Valley lake cycles were broadly synchronous with maximum episodes of glaciation, environmental conditions necessary to generate large lakes did not exist during early Wisconsin time.
Correlation of Alaskan varve Thickness with Climatic Parameters, and use in Paleoclimatic Reconstruction
Authors: Perkins James A. , Sims John D.
Published: December 2004

The thickness of varves in the sediments of Skilak Lake, Alaska, are correlated with the mean annual temperature (r = 0.574), inversely correlated with the mean annual cumulative snowfall (r = −0.794), and not correlated with the mean annual precipitation (r = 0.202) of the southern Alaska climatological division for the years 1907–1934 A.D. Varve thickness in Skilak Lake is sensitive to annual temperature and snowfall because Skilak Glacier, the dominant source of sediment for Skilak Lake, is sensitive to these climatic parameters. Trends of varve thickness are well correlated with trends of mean annual cumulative snowfall ( = −0.902) of the southern Alaska climatological division and with trends of mean annual temperature of the southern ( = 0.831) and northern ( = 0.786) Alaska climatological divisions. Trends of varve thickness also correlate with trends of annual temperature in Seattle and North Head, Washington ( = 0.632 and 0.850, respectively). Comparisons of trends of varve thickness with trends of annual temperature in California, Oregon, and Washington suggest no widespread regional correlation. Trends of annual snowfall in the southern Alaska climatological division and trends of annual temperature in the southern and northern Alaska climatological divisions are reconstructed for the years 1700–1906 A.D. Climatic reconstructions on the basis of varve thickness in Skilak Lake utilize equations derived from the regression of series of smoothed climatological data on series of smoothed varve thickness. Reconstruction of trends of mean annual cunulative snowfall in the southern Alaska climatological division suggests that snowfall during the 1700s and 1800s was much greater than that during the early and mid-1900s. The periods 1770–1790 and 1890–1906 show marked decreases in the mean annual snowfall. Reconstructed trends of the annual temperature of the northern and southern Alaska climatological divisions suggest that annual temperatures during the 1700s and 1800s were lower than those of the early and mid-1900s. Two periods of relatively high annual temperatures coincide with the periods of low annual snowfall thus determined.
Identification of Density-Stratified Waters in the Late-Pleistocene North Atlantic: A faunal Derivation
Authors: Morley Joseph J.
Published: December 2004

An expanded study of the radiolarian Cycladophora davisiana in late-Pleistocene North Atlantic marine sediments shows that over the last several hundred thousand years this species exhibits large variations in relative abundance. The C. davisiana curves in the North Atlantic cores are quite similar, with easily recognizable features common to all records. Minor deviations from the general pattern of this species' abundance apparently reflect the response of C. davisiana to specific oceanographic conditions characteristic of a particular area within the North Atlantic. C. davisiana occurs today in high abundance (>20%) only in the Sea of Okhotsk. Extensive winter and early spring sea-ice cover coupled with low surface-water salinities during summer and fall is responsible for maintaining near-freezing subsurface temperatures in this northwest Pacific marginal sea as well as relatively stable temperatures and salinities at depths below a shallow subsurface temperature minimum. During periods in the late Pleistocene, high C. davisiana abundances (>20%) in the North Atlantic were probably associated with oceanographic properties similar to those that exist in the Sea of Okhotsk today. Because of the relationship between relatively stable subsurface temperatures and salinities and high abundance levels of C. davisiana, analysis of this species' abundance pattern at several locations throughout the high-latitude North Atlantic should assist in identifying source areas of deep-water formation and determining the duration of deep convective processes at these sites.
Multiple Deglaciations of the Hudson Bay Lowlands, Canada, Since Deposition of the Missinaibi (Last-Integlacial?) Formation
Authors: Andrews J. T. , Shilts W. W. , Miller G. H.
Published: December 2004

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

Seven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifersJuniperus occidentalis, Pinuscf.ponderosa, andP. monophylla. The pollen spectra of these Pleistocene middens are dominated byPinussp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), andArtemisiasp. Mesophytic conifers are represented by low macrofossil concentrations.Sequoiadendron giganteumis represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages.

The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest thatS. giganteumgrew at lower elevations along the western side of the range and thatP. monophyllawas more widely distributed in cismontane California during the Pleistocene.
Gradational Thresholds and Landform Singularity: Significance for Quaternary Studies
Authors: Begin Ze'ev B. , Schumm Stanley A.
Published: December 2004

Geomorphic threshold conditions have been identifed at which stream patterns change and gully initiation occurs. For both, the threshold conditions are defined by the parameter of “relative shear stress” which is a measure of the energy state of the system and is based on known values of stream slope and mean annual discharge (for patterns) or drainage area (for gullies). The probability of passing from a stream pattern to another, or from stable to gullied valley floors, is a smooth function of relative shear stress and so the thresholds separating the different states of the geomorphic systems are gradational. The singularity of landforms prevents the identification of a sharp threshold, and as a result landform sensitivity will differ within the same area and under the same conditions. Therefore, geomorphic predictions and postdictions will be uncertain, and Quaternary correlations will lack precision.
Oxygen-Isotope Analyses and Pleistocene Ice Volumes
Authors: Mix Alan C. , Ruddiman William F.
Published: December 2004

The oxygen-isotope record from fossil foraminifera in deep-sea sediments is commonly used as a proxy for global ice volume. The linkage between δ18O and ice volume, however, is probably nonlinear. We have developed a simple numerical model of the isotopic response of the oceans to ice-volume change. The major features it simulates are (1) the changing mean isotopic composition of snow as a function of ice volume (colder snow temperatures forced by climate change and higher-elevation accumulation areas imply more negative mean δ18O); (2) the nonequilibrium isotopic composition of ice sheets (the past history of an ice sheet is integrated into its mean isotopic composition, which introduces a lag of isotopic “ice volume,” i.e., the measured δ18O record, scaled to ice-volume units, behind true ice volume); (3) selective preservation of isotopically more negative (colder, higher-latitude) ice (this geographic effect can selectively amplify or dampen the isotopic response to the ice-volume signal). We illustrate the response of our model to simple hypothetical ice-volume transitions of ice growth and ice decay. Sensitivity tests are illustrated for all model parameters. The results suggest that oxygen-isotope records reproduce the general patterns of ice-volume change fairly accurately. The foraminiferal isotope record, however, may misrepresent the true amplitude of the ice-volume signal and lag true ice volume by 1000 to 3000 yr.
Deglaciation and Postglacial Timberline in the San Juan Mountains, Colorado
Authors: Carrara P.E. , Mode W.N. , Rubin Meyer , Robinson S.W.
Published: December 2004

Lake Emma, which no longer exists because of a mining accident, was a tarn in a south-facing cirque near the headwaters of the Animas River in the San Juan Mountains of southwestern Colorado. During the Pinedale glaciation, this area was covered by a large transection glacier centered over the Lake Emma region. Three radiocarbon dates on basal organic sediment from Lake Emma indicate that by ca. 15,000 yr B.P. this glacier, one of the largest in the southern Rocky Mountains, no longer existed. Twenty-two radiocarbon dates onPiceaandAbieskrummholz fragments in the Lake Emma deposits indicate that from ca. 9600 to 7800 yr B.P., from 6700 to 5600 yr B.P., and at 3100 yr B.P. the krummholz limit was at least 70 m higher than present. These data, in conjunction withPicea:Pinuspollen ratios from both the Lake Emma site and the Hurricane Basin site of J. T. Andrews, P. E. Carrara, F. B. King, and R. Struckenrath (1975,Quaternary Research5, 173–197) suggest than from ca. 9600 to 3000 yr B.P. timberline in the San Juan Mountains was higher than present. Cooling apparently began ca. 3000 yr B.P. as indicated by decreases in both the percentage ofPiceapollen andPicea:Pinuspollen ratios at the Hurricane Basin site (Andrewset al., 1975). Cooling is also suggested by the lack ofPiceaorAbiesfragments younger than 3000 yr B.P. at either the Lake Emma or the Hurricane Basin site.
Atmospheric Circulation Patterns During Glacial Inception: A Possible Candidate
Authors: Crowley Thomas J.
Published: December 2004

Models of atmospheric circulation in the North Atlantic sector during glacial inception can be expanded to a hemispheric scale with the aid of diagnostic studies of the present climate. The present “Greenland Above” (GA) atmospheric circulation type may be a candidate for the atmospheric circulation type required during glacial inception. The pattern is an amplification, with only minor phase shifts, of the present average winter circulation pattern in the extratropical Northern Hemisphere. Southerly flow in the northwest Atlantic is associated with warm ocean temperatures, low sea ice in the Davis Strait, and increased precipitation over northeast Canada. Evidence from modeling of the present climate indicates that the GA pattern could be maintained by increased snow cover over eastern North America. Enhanced snow cover, due to decreased Northern Hemisphere summer insolation, could cause a similar response on an ice-age time scale.
Eolian Evidence for Spatial Variability of Late Quaternary Climates in Tropical Africa
Authors: Pokras Edward M. , Mix Alan C.
Published: December 2004

Study of the eolian fraction of late Quaternary sediments from the tropical Atlantic reveals that two modes of long-term climate variability have existed in tropical Africa during the last 150,000 yr. Tropical northwest Africa (i.e., the southwestern Sahara and Sahel) was driest during glaciations and stades, but wetter than at present during interglaciations and interstades. This may be a response to ice sheets at higher latitudes, via equatorward displacement of the westerlies and the subtropical high. In contrast, central equatorial Africa (southeast of the Sahara) was most arid during interstades and times of ice growth, and most humid during deglaciation. Wet periods in this area correspond to insolation maxima in northern hemisphere summer. A 23,000-yr precessional rhythm is suggested, supporting a direct link between African Monsoon intensity and orbitally modulated insolation. The late Holocene is the only time observed when both areas are arid during an interglacial episode. This may reflect, in part, anthropogenic disturbance of late Holocene climates.
Late Pleistocene Chronology and Environment of the “Ice-Free Corridor” of Northwestern Alberta
Authors: White James M. , Mathewes Rolf W. , Mathews W. H.
Published: December 2004

Pollen and macrofossil analyses of two radiocarbon-dated lake sediment cores in the upper Peace River district were used to investigate the controversial late-glacial geochronology of the “ice-free corridor.” The basal mineral-rich sediments contain reworked, radiogenically “dead” palynomorphs, as well as intrusive “modern” carbon. Analyses of the basal sediments from Boone Lake show that two 14C ages greater than 12,000 yr B.P. are spuriously old due to contamination by organic matter of Cretaceous age. The data support occlusion or near occlusion of Laurentide and Cordilleran ice in the Peace River area during the late Wisconsinan period. The sediment record began around 12.000 yr B.P. in the ice-dammed and enlarged Boone Lake. An initially open, sedge-dominated cover was invaded by sage, willow, grass, and poplar by 11,700 yr B.P., suggesting that a habitable landscape has existed in the area for at least 12 millennia. The data, however, do not support the ice-free corridor arguments of B. O. K. Reeves (1973, Arctic and Alpine Research 5, 1–16; 1983, In “Quaternary Coastlines and Marine Archaeology: Towards the Prehistory of Land Bridges and Continental Shelves” (P. M. Masters and N. C. Fleming, Eds.), pp. 389–411. Academic Press, New York), who suggests that ice occlusion did not occur in the Peace River Valley during the last 55,000 yr.
Speciation and Age Revision of the Atacaman SnailBostryx variabilisHerm
Authors: Craig Alan K.
Published: December 2004

Field evidence from the Atacama Desert of northern Chile indicates that the stratigraphic position of the land snailBostryx variabilisHerm has been incorrectly assigned to a marine series of the lower Pleistocene. Isotopic dating proves that the snail is a recently extinct Holocene taxon requiring no special paleoenvironmental explanations for its presence. However, the snail appears to offer an example of stress-induced speciation in confirmation of the “punctuated equilibrium” theory of evolution. It was probably transported from a fog oasis mountain habitat to a lower, hyperarid hostile environment by a sudden mudflow.
Tephrochronology of the Western Gulf of Mexico for the Last 185,000 Years
Authors: Rabek Karen , Ledbetter Michael T. , Williams Douglas F.
Published: December 2004

Tephra in 31 piston cores from the western Gulf of Mexico and 7 piston cores from the equatorial Pacific were analyzed by electron microprobe. Six ash layers in the western Gulf of Mexico were easily distinguished by TiO2, FeO, and CaO contents and correlated by geochemistry in order to determine the distribution pattern for each ash layer. Correlation by geochemistry is an easier, more accurate method than biostratigraphic correlation; some of the tephras were miscorrelated by biostratigraphy. The six tephras were dated by geochemical identification in a piston core with oxygen-isotope stratigraphy and the ages are Y5 (30,000 yr B.P.), Y6 (65,000 yr B.P.), Y8 (84,000 yr B.P.), X2 (110,000 yr B.P.), W1 (136,000 yr B.P.), and W2 (185,000 yr B.P.). Data from this study corroborated correlations of the Y8 tephra in the western Gulf of Mexico with the D layer in the eastern equatorial Pacific Ocean. None of the other five layers in the Gulf of Mexico, however, were found in the Pacific Ocean. The limited distribution of the Y5, Y6, X2, and W2 ash layers close to Mexico indicates possible sources in Mexico. Tephra from the late Pleistocene La Primavera pumice in Mexico, however, does not correlate with the marine tephra.
Mass Balance and Sliding Velocity of the Puget Lobe of the Cordilleran Ice Sheet During the Last Glaciation
Authors: Booth Derek B.
Published: December 2004

An estimate of the sliding velocity and basal meltwater discharge of the Puget lobe of the Cordilleran ice sheet can be calculated from its reconstructed extent, altitude, and mass balance. Lobe dimensions and surface altitudes are inferred from ice limits and flow-direction indicators. Net annual mass balance and total ablation are calculated from relations empirically derived from modern maritime glaciers. An equilibrium-line altitude between 1200 and 1250 m is calculated for the maximum glacial advance (ca. 15,000 yr B.P.) during the Vashon Stade of the Fraser Glaciation. This estimate is in accord with geologic data and is insensitive to plausible variability in the parameters used in the reconstruction. Resultant sliding velocities are as much as 650 m/a at the equilibrium line, decreasing both up- and downglacier. Such velocities for an ice sheet of this size are consistent with nonsurging behavior. Average meltwater discharge increases monotonically downglacier to 3000 m3/sec at the terminus and is of a comparable magnitude to ice discharge over much of the glacier's ablation area. Paleoclimatic inferences derived from this reconstruction are consistent with previous, independently derived studies of late Pleistocene temperature and precipitation in the Pacific Northwest.
Modern Alluvial History of the Paria Rver Drainage Basin, Southern Utah
Authors: Hereford Richard
Published: December 2004

Stream channels in the Paria River basin were eroded and partially refilled between 1883 and 1980. Basin-wide erosion began in 1883; channels were fully entrenched and widened by 1890. This erosion occurred during the well-documented period of arroyo cutting in the Southwest. Photographs of the Paria River channel taken between 1918 and 1940 show that the channel did not have a floodplain and remained wide and deep until the early 1940s. A thin bar (<50 cm), now reworked and locally preserved, was deposited at that time. Basin-wide aggradation, which began in the early 1940s, developed floodplains by vertical accretion. The floodplain alluvium, 1.3–3 m thick. consists of two units recognizable throughout the studied area. An older unit was deposited during a time of low flow and sediment yield whereas the younger unit was deposited during times of high flow, sediment yield, and precipitation. Tree-ring dating suggests that the older unit was deposited between the early 1940s and 1956, and the younger between 1956 and 1980. The units are not time transgressive, suggesting that deposition by knickpoint recession was not an important process. High peak-flood discharges were associated with crosion and low flood discharges with aggradation. The erosional or aggradational mode of the streams was determined principally by peak-flood discharge, which in turn was controlled by precipitation.
Late Holocene Sea-Level Changes in the Northwest Tuamotu Islands, French Polynesia
Authors: Pirazzoli Paolo Antonio , Montaggioni Lucien François
Published: December 2004

Field surveys of several sea-level indicators (exposed in situ reef framework, conglomerates, coral colonies and Tridacna shells in a growth position, sea-corrosion notches) carried out on six atolls from the NW Tuamotus (Mataiva, Rangiroa, Arutua, Kaukura, Apataki and Takapoto) and data from four subsurface boreholes drilled through Mataiva show that during the late Holocene mean sea level (MSL) reached a maximum elevation at approximately + 0.9 m. It remained above the present MSL from between 6000 and 5500 yr B.P. until at least 1200 yr B.P. Human settlements on the atolls were extremely unlikely and probably impossible throughout this time. The area investigated seems to have been tectonically quite stable during the late Holocene. A local curve of MSL variations may be representative of the regional eustatic pattern.
Magnetic Polarity Stratigraphy of the Pleistocene Section at Portland (Victoria), Australia
Authors: MacFadden Bruce J. , Whitelaw Michael J. , McFadden Phil , Rich Thomas H. V.
Published: December 2004

Three to seven oriented paleomagnetic samples were collected from 16 sites in the Nelson Bay and Bridgewater formations at Portland, Victoria, which contains the recently discovered Nelson Bay local fauna (L.F.). The entire section has reversed polarity. These results, along withGloborotalia truncatulinoideswithin the section, and the presence of underlying middle Pliocene-dated basalts, indicate that the Portland section, and the included Nelson Bay L.F., was deposited within the late Matuyama Chron between 1.66 and 0.73 myr ago. This represents the first well-documented pre-14C Pleistocene mammalian fauna in Australia calibrated in direct stratigraphic context with absolute dating methods. In addition, the reversed polarity for the Bridgewater Formation confirms the previous hypothesis that the depositional history of this beach-sand deposit is time-transgressive across the Brunhes-Matuyama boundary.
Chronostratigraphic Studies of Sediments in the Negev Desert, Using Amino Acid Epimerization Analysis of Land Snail Shells
Authors: Goodfriend Glenn A.
Published: December 2004

The chronostratigraphy of mostly Holocene sediments in the Northern Negev desert of Israel was studied through amino acid epimerization analysis (alloisoleucine/isoleucine ratio, A/I) of individual land snail shells and14C analysis of bulk samples of land snail shells contained within the sediments. Analysis of 31 deposits shows a very strong correlation between A/I and14C age. A/I analyses indicate that age mixtures occur within all colluvial and in some fluvial deposits. Consequently, radiocarbon dates of bulk samples, which give an average age, overestimate the time of deposition. Sedimentation rates were generally rapid in both fluvial and colluvial deposits. Colluviation shows a maximum in the early Holocene and decreases progressively thereafter, in accordance with the change in average rainfall. Accumulation of fluvial sediments shows a distinct mid-Holocene maximum and apparently relates to the interaction between variation in rainfall, extent of bedrock exposure, and vegetation density. Late Holocene fluvial deposition may relate to agricultural activity. The understanding of the chronology of sedimentation is dependent on an integrated approach employing amino acid epimerization analysis to study age variation within a layer and14C analyses for establishment of an absolute chronology.
Magnetic Stratigraphy and a Test for Block Rotation of Sedimentary Rocks within the San Andreas Fault Zone, Mecca Hills, Southeastern California
Authors: Chang Shih-Bin R. , Allen Clarence R. , Kirschvink Joseph L.
Published: December 2004

A 500-m section of the Palm Spring Formation in the southern Mecca Hills, located within the San Andreas fault zone in southeastern California, has been paleomagnetically sampled to determine possible tectonic rotation in this area and to establish time-stratigraphic control. This work was partly stimulated by the fact that 80 km farther south, previous studies demonstrated 35° of postdepositional rotation in the Palm Spring Formation of the Vallecito-Fish Creek basin east of the Elsinore fault. Several lines of evidence suggest that hematite is the main magnetic carrier of the Mecca Hills samples. Large anhedral hematite grains observed in magnetic extracts and a positive fold test imply a detrital origin of the remanence. The polarity reversal patterns, together with earlier vertebrate paleontologic studies, restrict the time span for deposition of this unit to the middle-late Matuyama chron (2.0–0.75 myr ago), thus of uppermost Pliocene and early Pleistocene age. Characteristic directions of best least-squares fit for 73 samples suggest little or no overall rotation, despite the severe late Quaternary tectonic activity demonstrated by the intense deformation of these strata.
Late Holocene Sea-Level Record in a Core from the Puget Lowland, Washington
Authors: Eronen Matti , Kankainen Tuovi , Tsukada Matsuo
Published: December 2004

Diatoms and lithological facies of an 8.45-m core collected from Shine swamp (47°52′20″N lat, 122°41′45″W long; about 2 m above the mean tide level) in the northern Puget Lowland reveal a rise in relative sea level during the past 6000 yr. A layer of fresh-water peat at a depth of 6.6-6.3 m (ca. 7000-5000 yr B.P.) indicates a low stand of the sea in early and middle Holocene time. About 5000 yr ago the rise in relative sea level resulted in accumulation of subtidal or lower intertidal clayey gyttja and gyttja which contain mainly marine and brackish-water diatoms (80–95%). By about 3500 yr B.P., the basin had shoaled to upper intertidal levels, and peat began to accumulate again while the sea continued its relative rise. During the period of this continuous peat growth, several alterations in fresh-water and marine/brackish-water diatom assemblages took place, indicating slight differences in the contemporaneous sea-level rise and vertical peat growth.
A 20th-Century Record of Climatologically Modulated Sediment Accumulation Rates in a Canadian Fjord
Authors: Smith John N. , Schafer Charles T.
Published: December 2004

The geochronology of a gravity core collected from an anoxic, high sedimentation rate (>2.5 cm/yr) setting near the head of the Saguenay Fjord in Quebec has been established for the period 1900–1979 to a resolution of better than 1 yr using a constant flux 210Pb model. Interannual variations of the sedimentation rate of between 28 and 50% are caused by rapid inputs of coarse silt and fine sand during spring freshet events. A significant correlation between sand percentage and sediment accumulation rate reflects the increase in stream competence during the spring freshet; the sand percentage parameter can be used in conjunction with sediment size parameters to estimate temporal variations in river discharge intensity. Between 1914 and 1979 sediment accumulation rates were about 60% higher during the spring and summer compared to fall and winter seasons. Both the magnitude of the Saguenay River spring discharge and the quantity of precipitation stored as snow decrease through the 20th century suggesting that the freshet intensity was governed largely by natural rather than anthropogenic (e.g., dam construction) factors. A direct correlation between sand flux, peak river discharge, and a snow storage parameter provides a link between sediment texture and climate. Detailed analyses of the grain-size distributions for dated core intervals offer a method for the reconstruction of a proxy record of paleodischarge for the Saguenay River spring freshets.
Age and Significance of Fossil White Spruce (Picea glauca), Tunica Hills, Louisiana-Mississippi
Authors: Givens Charles R. , Givens Florence Montgomery
Published: December 2004

Radiocarbon dates indicate a Farmdalian through Woodfordian age for fossil white spruce (Picea glauca) in the Tunica Hills, a greater time span than previously documented. These dates, furthermore, require revision of the ages of fluvial terrace deposits in the region. Spruce-bearing Terrace 1 sediments, previously regarded as late Woodfordian to Holocene age, are of Farmdalian to late Holocene age. Terrace 2 sediments, previously assigned a Sangamonian or Farmdalian age, are of probable Altonian age. Plant fossils in Terrace 1 sediments represent two climatically and temporally distinct assemblages: a cool-temperate, Farmdalian-Woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak-hickory association; and a warm-temperate Holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the Tunica Hills. Locally, fossils of white spruce have been reworked into younger Terrace 1 sediments containing the warm-temperate plant assemblage. The transition from the cool-temperate flora to the modern warm-temperate flora in the Tunica Hills probably occurred around 12,000 yr B.P.
Changing Holocene Snail Faunas and Environments Along the Eastern Caprock Escarpment of Texas
Authors: Neck Raymond W.
Published: December 2004

Detailed study of gastropods recovered from the Lake Theo Site, Briscoe County, Texas, has revealed a progressive decline in species diversity from early Holocene to the present. Knowledge of the microhabitats preferred by the recovered species allows a partial reconstruction of environments required to produce such communities. Since the early Holocene, the Lake Theo area has experienced a progressive loss of deciduous riparian gallery woodland habitat. Alteration in plant communities was caused by a dramatic decrease in effective precipitation. Analysis of the sequence of local extirpation of the various snail species indicates that the decrease in precipitation and increase in temperature probably were not concurrent.
Holocene Relative Sea-Level Fluctuations in the St. Lawrence Estuary, Québec, Canada
Authors: Dionne J.C.
Published: December 2004

Between 7000 and 6000 yr B.P., relative sea level was as much as 5 m lower than today in the St. Lawrence estuary, Québec. A small transgression (Laurentian transgression) occurred between 5800 and 4400 yr B.P., which resulted in the construction of an 8- to 10-m terrace. About 3000 yr B.P., relative sea level was similar to present, and then a stillstand or a slight rise occurred during which a cliff (Micmac cliff) was cut into the emerged terrace. During a subsequent lowering of relative sea level (coastal emergence), a low aggradational terrace (Mitis terrace) was built between 2300 and 1500 yr B.P. at the base of the Micmac cliff. A new emergence curve for the south shore of the St. Lawrence estuary showing a mid-Holocene high stand of relative sea level is therefore proposed.
Interstadial Conifer Wood from Northern Maine
Authors: Anderson R. Scott , Davis Ronald B. , Stuckenrath Robert , Borns Harold W.
Published: December 2004

Conifer wood, probably spruce (Piceasp.), of middle Wisconsinan age (29,200 ± 500 yr B.P.) was recovered from late-glacial lake sediments from Upper South Branch Pond, Maine. If the wood was derived from a local source, deglaciation of part of northern New England is suggested for this time. The occurrence also has implications for understanding the problem associated with radiocarbon dating of bulk lake sediment containing small amounts of organic matter.
Late Quaternary Ice-Surface Fluctuations of Beardmore Glacier, Transantarctic Mountains
Authors: Denton George H. , Bockheim James G. , Wilson Scott C. , Leide James E. , Andersen Björn G.
Published: December 2004

Former longitudinal profiles of Beardmore Glacier, an outlet through the Transantarctic Mountains, constrain polar plateau elevations near the center of Antarctica and ice-shelf grouding in the southern Ross Embayment. Three gravel drift sheets of late Quaternary age occur alongside Beardmore Glacier. Plunket drift, the youngest, is parallel to and 7–30 m above the present ice surface. The upper limit of Beardmore drift, intermediate in age, is within 35–40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth. The upper limit of Meyer drift, the oldest, is parallel to and 30–50 m above Beardmore drift. From correlation with numerically dated drifts farther north, we assign an early Holocene age to Plunket drift, a late Wisconsin age to Beardmore drift, and an age of marine isotope Stage 6 to Meyer drift. By our age model, Beardmore Glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by Beardmore and Meyer drifts. Most likely, grounded ice in the southern Ross Embayment caused such thickening of Beardmore Glacier almost to the polar plateau. A concomitant decline in precipitation is implied by ice-cap retreat on the nearby Dominion Range and is consistent with little change of upper Beardmore Glacier. Ice-shelf grounding most likely resulted from lowered sea level and/or basal melting. Lower than present precipitation was probably caused by colder air temperatures and more-distant open water. The Plunket profile records Holocene ice-surface lowering from increased surface ablation, decreased ice flow, or grounding-line recession.
Application of Tandem Accelerator Mass-Spectrometer Dating to Late Pleistocene-Holocene Sediments of the East Antarctic Continental Shelf
Authors: Domack E. W. , Jull A. J. T. , Anderson J. B. , Linick T. W. , Williams C. R.
Published: December 2004

Glacial recession from the Antarctic continental shelf is recorded by glacial-marine diamictons, sands, and overlying siliceous oozes. In order to clarify the chronology for this sequence, use was made of the University of Arizona tandem accelerator mass-spectrometer (TAMS) for 14C dating. Small samples of benthic and planktonic foraminifera were selectively removed from diamictons, graded sands, and surface sediments which were recovered from the Wilkes Land continental shelf and slope, East Antarctica. Organic carbon was also utilized as a source for TAMS dating of the siliceous oozes and muds. Uncorrected ages varied from 14,260 ± 140 to 3230 ± 200 yr B.P. Carbon fixed by phytoplankton and foraminifera is strongly influenced by old, glacial-derived CO2. Thus, reservoir corrections of up to 5500 yr are needed for the 14C dates. Iceberg turbation reworks foraminifera so that dates from resulting deposits (diamictons) are interpreted as maximum ages. The consistency of corrected ages from the shelf, along with the sedimentologic interpretation, suggests a rather recent recession, perhaps mid-Holocene for this portion of the East Antarctic ice sheet. Further application of the TAMS method should help clarify other problems concerning the late Quaternary glacial history of Antarctica.
Geoarchaeological Evidence for Prairie-Mound Formation in the Mississippi Alluvial Valley, Southeastern Missouri
Authors: O'Brien Michael J. , Lyman R. Lee , Holland Thomas D.
Published: December 2004

Archaeological materials in several prairie mounds in the northern Western Lowlands of southeastern Missouri indicate that mounds began forming prior to ca. 5000-3000 yr B.P. The mounds subsequently were inundated and built up to their modern configuration by aggradational and reworking processes. Human use of the mounds may have been tied to exploitation of aquatic animals residing in backwater habitats during periods of prolonged flooding. Principal features of the sampled portion of the mound field include preoccupation topographic highs, early occupation (ca. 5000-3000 yr B.P.) layers that drape the topographic highs, and later occupation (ca. 3000-950 yr B.P.) layers that drape earlier occupation layers and extend onto intermound areas.
Trends in Chesapeake Bay Sedimentation Rates during the Late Holocene
Authors: Donoghue Joseph F.
Published: December 2004

Trends are discernible in the estimates of late Holocene rates of sedimentation and sea-level rise for the Chesapeake Bay. During most of the Holocene Epoch sedimentation rates and relative sea-level rise were equal, within the limits of measurement, at approximately 1 mm yr−1. Sedimentation rates measured over the past century, however, are nearly an order of magnitude higher, while the rate of relative sea-level rise for the Chesapeake Bay now averages 3.3 mm yr−1, as measured on long-term tide gauge records. When the acceleration in these rates occurred is uncertain, but it appears to have been confined to the past millennium, and probably to the past few centuries. The rapid sedimentation rates recorded during historic time may be a temporary disequilibrium that has resulted from a recent acceleration in the rate of relative sea-level rise.
Electron Spin Resonance (ESR) Dating of Hominid-Bearing Deposits in the Caverna delle Fate, Ligure, Italy
Authors: Falgueres Christophe , Yokoyama Yuji , Bibron Roland
Published: December 2004

Stalagmitic floors interstratified with Mousterian deposits from the Caverna delle Fate (Italy) have been dated by the electron spin resonance (ESR) method. Three samples dated fall between 60,000 and 74,000 yr and indicate the age of the Mousterian deposits. They are in good agreement with ages determined by nondestructive γ-ray spectrometry of the human remains from 231Pa/235U and 230Th/234U ratios, which are, respectively, yr. These dates are consistent with the morphological characteristics of the bones as Neanderthal remains.
Paleomagnetic Evidence for Repeated Glacial Lake Missoula Floods from Sediments of the Sanpoil River Valley, Northeastern Washington
Authors: Steele William K.
Published: December 2004

Recent explanations of widespread rhythmically layered sediments in eastern Washington as the result of repeated great floods from glacial Lake Missoula implicitly suggest a paleomagnetic test for validity. If each conjectural flood layer is separated by years or decades, as hypothesized, a sequence of several such flood beds should record measurable secular variation in geomagnetic field direction. In the Sanpoil River valley where the rhythmite sequences are thought to have been deposited in glacial Lake Columbia, the paleomagnetic test consists of measuring remanent magnetization (RM) directions for thick, upwardly fining beds inferred to be sediments deposited by the influx of flood waters from glacial Lake Missoula into glacial Lake Columbia. Laboratory measurements of samples from three widely spaced sections along the Sanpoil River yield RM vectors with erratic inclinations, apparently affected by varying contributions of inclination error and (or) compaction shallowing, but with declinations that generally differ statistically from one flood to the next and that show the same west-to-east trend at all three locations. The rates of declination change inferred from these data are consistent with modern rates, thus providing the first geophysical evidence supporting the timing in the tens-of-floods theory.
Marine Episodes in Hudson Strait and Hudson Bay, Canada, during the Wisconsin Glaciation
Authors: Laymon Charles A.
Published: December 2004

Twelve reworked shell fragments were recovered from five till samples collected on Nottingham Island in western Hudson Strait, Canada. Total hydrolysate amino acid ratios (D-alloisoleucine/L-isoleucine) for each fragment range from 0.043 to 0.154 and are significantly higher than ratios for radiocarbon-dated Holocene shells, which average 0.022. One shell fragment with an aIle/Ile ratio of 0.065 yielded an AMS radiocarbon age of 44,200 ± 2300 yr B.P. (AA-3254). Absolute age estimates based on the amino acid ratios are constrained by reasonable limits on the estimated effective diagenetic temperature of the fossils. On this basis, the shell fragments are correlated with oxygen isotope substages 5e and 5a and stage 3 in the preferred hypothesis. Theses results independently support hypotheses calling for at least partial deglaciation and marine incursion in Hudson Strait and Hudson Bay at these times.
Coastal Aminostratigraphy of the Last Interglaciation in Southern Australia
Authors: Murray-Wallace Colin V. , Belperio Antonio P. , Picker Kelvin , Kimber Ronald W.L.
Published: December 2004

Amino acid racemization data for marine molluscs of the last interglaciation from southern Australia provide the basis for a predictive model for relative dating of late Quaternary sequences. Genera analyzed includeAnadarasp.,Katelysiasp.,Glycymerissp., andFulviasp. that exhibit moderate racemization rates. A genus effect on racemization is not evident in these taxa. Coefficients of variation for intershellD/Lratio variation for each deposit are generally less than 12%. The extent of racemization in molluscan fossils of the last interglaciation from temperate coastal settings in southern Australia represents an exponential function of temperature and is in general accord with data from Northern Hemisphere sites with similar contemporary mean annual temperature values. These data highlight the potential of amino acid racemization for global correlation programs. The amino acid data from southern Australia suggest, however, that a larger margin of variation may have to be accounted for in stratigraphic correlation, as indicated by the greater scatter of data around the oxygen isotope substage 5eisochron. These data have implications regarding the age-resolving power of amino acid racemization.
Chronological Separation of Interglacial Raised Beaches from Northwestern Europe Using Thermoluminescence
Authors: Balescu Sanda , Packman Susan C. , Wintle Ann G.
Published: December 2004

Thermoluminescence (TL) age estimates have been obtained on coarse-grained detrital feldspar from Eemian beach sand (substage 5e), early Weichselian dune sands (substages 5d and 5b), and pre-Eemian beach sand. The past radiation dose is obtained using the additive dose method. Even for the oldest samples, which date to 300,000 yr B.P. by other methods, the TL signal is not in saturation and can be doubled by the addition of laboratory radiation doses without saturation being achieved. This is contrasted with the behavior of polymineral, silt-sized grains from loess in the adjacent area. The TL age estimates are systematically underestimated by about 40% when compared with the expected geological ages. However, they are in correct stratigraphic order and demonstrate that stage 5 beach deposits can be distinguished from those resulting from earlier high sea levels using TL signals from potassium feldspars.