Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska     

Florence R. Weber  Thomas D. Hamilton  David M. Hopkins  Charles A. Repenning  Herbert Haas 《Quaternary Research》1981,16(2):167-180

The Canyon Creek vertebrate-fossil locality is an extensive road cut near Fairbanks that exposes sediments that range in age from early Wisconsin to late Holocene. Tanana River gravel at the base of the section evidently formed during the Delta Glaciation of the north-central Alaska Range. Younger layers and lenses of fluvial sand are interbedded with arkosic gravel from Canyon Creek that contains tephra as well as fossil bones of an interstadial fauna about 40,000 years old. Solifluction deposits containing ventifacts, wedge casts, and rodent burrows formed during a subsequent period of periglacial activity that took place during the maximum phase of Donnelly Glaciation about 25,000–17,000 years ago. Overlying sheets of eolian sand are separated by a 9500-year-old paleosol that may correlate with a phase of early Holocene spruce expansion through central Alaska. The Pleistocene fauna from Canyon Creek consists of rodents (indicated by burrows), Mammuthus primigenius (woolly mammoth), Equus lambei (Yukon wild ass), Camelops hesternus (western camel), Bison sp. cf. B. crassicornis (large-horned bison), Ovis sp. cf.O. dalli (mountain sheep), Canis sp. cf. C. lupus (wolf), Lepus sp. cf. L. othus or L. arcticus (tundra hare), and Rangifer sp. (caribou). This assemblage suggests an open landscape in which trees and tall shrubs were either absent or confined to sheltered and moist sites. Camelops evidently was present in eastern Beringia during the middle Wisconsin interstadial interval but may have disappeared during the following glacial episode. The stratigraphic section at Canyon Creek appears to demonstrate that the Delta Glaciation of the north-central Alaska Range is at least in part of early Wisconsin age and was separated from the succeeding Donnelly Glaciation by an interstadial rather than interglacial episode.  相似文献   

Subsidence and strike-slip tectonism of the upper continental slope off Manzanillo, Mexico     

William L. Bandy  Franois Michaud  Jacques Bourgois  Thierry Calmus  Jrme Dyment  Carlos A. Mortera-Gutirrez  Jose Ortega-Ramírez  Bernard Pontoise  Jean-Yves Royer  Bertrand Sichler  Marc Sosson  Mario Rebolledo-Vieyra  Florence Bigot-Cormier  Oscar Díaz-Molina  Angel D. Hurtado-Artunduaga  Guillermo Pardo-Castro  Corrine Trouillard-Perrot 《Tectonophysics》2005,398(3-4):115-140

The direction of convergence between the Rivera and North American plates becomes progressively more oblique (in a counter-clockwise sense as measured relative to the trench-normal direction) northwestward along the Jalisco subduction zone. By analogy to other subduction zones, the forces resulting from this distribution of convergence directions are expected to produce a NW moving, fore-arc sliver and a NW–SE stretching of the fore-arc area. Also, a series of roughly arc parallel strike-slip faults may form in the fore-arc area, both onshore and offshore, as is observed in the Aleutian arc.In the Jalisco subduction zone, the Jalisco block has been proposed to represent such a fore-arc sliver. However, this proposal has encountered one major problem. Namely, right-lateral strike-slip faulting within the fore-arc sliver, and between the fore-arc sliver and the North American plate, should be observed. However, evidence for the expected right-lateral strike-slip faulting is sparse. Some evidence for right-lateral strike-slip faulting along the Jalisco block–North American plate boundary (the Tepic–Zacoalco rift system) has been reported, although some disagreement exists. Right-lateral strike-slip faulting has also been reported within the interior of the Jalisco block and in the southern Colima rift, which forms the SE boundary of the Jalisco block.Threefold, multi-channel seismic reflection data were collected in the offshore area of the Jalisco subduction zone off Manzanillo in April 2002 during the FAMEX campaign of the N/O L'Atalante. These data provide additional evidence for recent strike-slip motion within the fore-arc region of the Jalisco subduction zone. This faulting offsets right-laterally a prominent horst block within the southern Colima rift, from which we conclude that the sense of motion along the faulting is dextral. These data also provide additional evidence for recent subsidence within the area offshore of Manzanillo, as has been proposed.  相似文献   

A Comparative Analysis of Curbside Recycling Behavior in Urban and Suburban Communities*     

Florence M. Lansana 《The Professional geographer》1993,45(2):169-179

This study explores the variations in household participation rates in recycling projects implemented in urban and suburban communities. A causal model is developed to compare the demographic attributes of residents, their awareness of the recycling programs, their environmental attitudes, and their overall willingness to recycle. The model is assessed by Linear Structural Equations Methodology (LISREL). The results suggest that household recycling behavior is not consistent across communities due primarily to variations in demographic characteristics of residents and their evaluation of program policies.  相似文献   

Ground penetrating radar sounding of a temperate glacier; modelling of a multilayered medium1     

Florence Nicollin  Wlodek Kofman 《Geophysical Prospecting》1994,42(7):715-734

A numerical simulation of electromagnetic propagation through a multilayered medium is performed in order to explain and interpret the signal received from the radar sounding of a temperate glacier. During the winter of 1990, several radar profiles were obtained on the Mont-de-Lans glacier in the French Alps with a ground penetrating radar which uses a phase modulation of the transmitted pulse by coded sequences. The pulse compression is obtained by applying the matched filter to the received signal, which provides a range-resolution of about 8 m in the ice. The profiles recorded on the temperate glacier do not show a single clear reflection from the ice-bedrock interface, but they exhibit widely distributed energy decreasing with depth. This may be due to the inhomogeneous inner structure of the temperate glacier and we use a simple model of a layered medium to compute a simulation of the propagation. Thus, partial reflection at each layer and scattering from a rough basal interface may explain the observed signal. A computer-based technique is used to locate on the data the bottom of the glacier in order to estimate the ice thickness. The results from the different radar profiles are consistent and are a good fit to the thickness which has been determined by other geophysical methods.  相似文献   

TEM and FESEM characterization of asbestiform and non-asbestiform actinolite fibers in hydrothermally altered dolerites (France)     

Didier Lahondère  Florence Cagnard  Guillaume Wille  Jéromine Duron  Maxime Misseri 《Environmental Earth Sciences》2018,77(10):385

This paper provides new mineralogical and morphological characterizations of calcic amphiboles from hydrothermally altered dolerites from France to discuss their potential to contain naturally occurring asbestos (NOA) and to release elongated mineral particles corresponding to asbestos fibers, or asbestos-like fibers, into the air. The calcic amphiboles were characterized using electron microprobe analysis, scanning and transmission electron microscopy. The results underline that fibrous occurrences of actinolite and ferro-actinolite regularly occur in hydrothermally altered dolerites, both in the groundmass and in quartz veins. In the groundmass, actinolitic amphiboles crystallize at the expense of magmatic clinopyroxenes and are rarely fibrous. Conversely, actinolite and ferro-actinolite fibers from quartz veins are potentially asbestiform to clearly asbestiform. The identification of quartz veins in hydrothermally altered dolerites is, therefore, an important parameter which should draw attention to the possible presence of asbestiform actinolite fibers. The mineralogical characterization of such veins as well as the estimation of their thickness and density is an important point to consider during studies involving NOA issues. Moreover, the degree of weathering of the dolerites, which directly affects the ability of non-asbestiform actinolite crystals to dissociate into very thin fibers, regarded as cleavage fragments instead of as asbestos, is also a key parameter to consider. Hydrothermally altered dolerites are common rocks likely to be exploited by the quarrying industry to produce aggregates or to be affected by construction works. Due to the abundance of actinolite fibers that they may contain locally, these rocks become priority targets to be monitored in terms of geological characterization and airborne fiber emission to ensure the protection of populations and workers.  相似文献   

Aquifer parameter estimation using tide-induced water-table fluctuations in the Biscayne Aquifer,Miami-Dade County,Florida (USA)     

Rogers  Martina  Sukop  Michael C.  Obeysekera  Jayantha  George  Florence 《Hydrogeology Journal》2023,31(4):1031-1049

The Biscayne Aquifer (Florida, USA) is a coastal, shallow, unconfined, and heterogeneous aquifer with high water tables, composed of less-permeable sand to highly permeable karstic limestone. These properties make the Biscayne Aquifer one of the world’s most productive groundwater resources. The aquifer’s high yield and non-Darcian flow cause challenges for estimating aquifer parameters, which are essential for understanding groundwater processes and managing and protecting the groundwater resources. Water-table fluctuations in the Biscayne Aquifer are associated with astronomical tidal forces and gate operations on canal water-control structures. Analysis of observed groundwater level fluctuations can provide an understanding of the connectivity between the aquifer, Biscayne Bay, and the water level in the canals. Further, groundwater level fluctuations can be used for aquifer parameter estimation. In this research, observed ocean water levels measured at tidal stations and groundwater levels are fitted to Jacob’s analytical solution, where the amplitude of the groundwater head fluctuation decreases exponentially, and the time lag increases with distance from the shore. Observed groundwater levels were obtained from monitoring wells along the Miami-Dade shore and the barrier island of Miami Beach. Results indicate that Jacob’s solution is effective for aquifer parameter estimation in Miami Beach, where monitoring wells are closer to the shore. Estimated hydraulic conductivity appears to increase by four orders of magnitude to approximately 1 m s^–1 as the distance from shore increases. Constructing monitoring wells closer to the shore in Miami-Dade County and elsewhere would permit improved aquifer parameter estimation and support enhanced groundwater modeling efforts.

  相似文献   

Influence of chronic exposure to silver and mercury in the field on the bioaccumulation potential of the bivalve Macoma balthica     

Florence Boisson  Mark G.J. Hartl  Scott W. Fowler  Claude Amiard-Triquet   《Marine environmental research》1998,45(4-5)

In order to assess the adaptation to metals previously observed in the bioindicator organism, Macoma balthica, subjected to chronic contamination by silver and mercury in the French Loire estuary, the bioaccumulation potential of individual organisms originating from the contaminated Loire estuary and a relatively uncontaminated control estuary (Somme) was evaluated using both radiotracers and stable isotopes of Ag (80 μg Ag litre⁻¹) and Hg (100 μg Hg litre⁻¹). Clams from the contaminated estuary were more sensitive to Ag (LT₅₀ = 9d) than those originating from the Somme estuary (LT₅₀ > 15d), even though the former bioaccumulated Ag to a significantly lower degree. This is attributed to a consequence of the chronic stress induced by Ag while clams were living in their natural environment. Therefore, past history of trace metal contamination should be considered when evaluating the susceptibility of M. balthica to heavy metal exposure. Lower uptake rates obtained for Hg (during the initial uptake phase only) and for Ag in clams from the polluted estuary suggest the presence of an adaptive trait for survival in contaminated areas. However, the lower degree of bioconcentration observed for Ag was not sufficiently low to reduce the sensitivity of the organisms to Ag and allow them to resist the toxic stress. Clams that survived Ag or Hg exposure at LT₅₀ did not protect themselves against metal toxicity by accumulating a significantly lesser amount of these metals than clams which did not survive metal stress. The results suggest that the bioaccumulation potential of each individual was not a factor which can explain the survival ability of M. balthica exposed to chronic Ag and Hg contamination in estuaries. In this case, cellular, biochemical and genetic levels of adaptation are presumed to be of greater importance.  相似文献   

The suitability of annual tree growth rings as environmental archives: Evidence from Sr,Nd, Pb and Ca isotopes in spruce growth rings from the Strengbach watershed     

Peter Stille  Anne-Désirée Schmitt  François Labolle  Marie-Claire Pierret  Sophie Gangloff  Florian Cobert  Eric Lucot  Florence Guéguen  Laure Brioschi  Marc Steinmann  François Chabaux 《Comptes Rendus Geoscience》2012,344(5):297-311

The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces’ root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution.  相似文献   

Global,regional and local scale factors determining glaciation extent in Eastern Siberia over the last 140,000 years     

Gerhard Krinner  Bernhard Diekmann  Florence Colleoni  Georg Stauch 《Quaternary Science Reviews》2011,30(7-8):821-831

The aim of this work is to evaluate the effect of variations of greenhouse gas concentrations, orbital parameters, sea-surface conditions, vegetation and dust deposition on the extent of East Siberian mountain glaciations during the late Quaternary. An atmosphere-only general circulation model is used in a series of 16 sensitivity tests at high spatial resolution over the region of interest to systematically evaluate the relative importance of these different forcing parameters. No attempt was made to reproduce in detail the history of late Quaternary mountain glaciations in East Siberia, because, given (a) the temporal and spatial scarcity of available evidence of mountain glaciations in this region and (b) the large uncertainties concerning the boundary conditions to be prescribed in this model, such an exercise must necessarily remain incomplete and partially inconclusive. The results of this study suggest that moisture delivery from the Atlantic is an important factor determining mountain glacier mass balance in Eastern Siberia and is very sensitive to the geometry of the West Eurasian ice sheet. This means that variable moisture blocking by the West Eurasian ice sheet during the Weichselian is the most important single factor explaining the opposite history of glacier and ice sheet extent in West and East Eurasia during the Weichselian. This work confirms earlier results showing that the large 140 kyr BP West Eurasian ice sheet caused regional-scale cooling extending towards Eastern Eurasia. Nevertheless, the simulated response of the regional summer temperature (and thus glacier extent because of the strong dependency of glacier mass balance of summer melt rates) is to a very large extent directly determined by insolation. For the Early Weichselian, this leads to a clear maximum of local glacier extent at 70 kyr BP, which is in line with the variations of top-of-the-atmosphere insolation on orbital time scales, but to some degree at odds with geological evidence which suggests larger glacier extent at 115 and 90 kyr BP than at 70 kyr BP. Through snow feedbacks, the effects of changes in the prescribed vegetation distribution and dust deposition rate are also substantial. In summary, it appears that the broad features of late Quaternary glaciation history in Eastern Eurasia can be understood in terms of known forcings.  相似文献   

The sensitivity of the Late Saalian (140?ka) and LGM (21?ka) Eurasian ice sheets to sea surface conditions   总被引：1，自引：1，他引：0  

Florence Colleoni  Johan Liakka  Gerhard Krinner  Martin Jakobsson  Simona Masina  Vincent Peyaud 《Climate Dynamics》2011,37(3-4):531-553

This work focuses on the Late Saalian (140?ka) Eurasian ice sheets?? surface mass balance (SMB) sensitivity to changes in sea surface temperatures (SST). An Atmospheric General Circulation Model (AGCM), forced with two preexisting Last Glacial Maximum (LGM, 21?ka) SST reconstructions, is used to compute climate at 140 and 21?ka (reference glaciation). Contrary to the LGM, the ablation almost stopped at 140?ka due to the climatic cooling effect from the large ice sheet topography. Late Saalian SST are simulated using an AGCM coupled with a mixed layer ocean. Compared to the LGM, these 140?ka SST show an inter-hemispheric asymmetry caused by the larger ice-albedo feedback, cooling climate. The resulting Late Saalian ice sheet SMB is smaller due to the extensive simulated sea ice reducing the precipitation. In conclusion, SST are important for the stability and growth of the Late Saalian Eurasian ice sheet.  相似文献