Late Quaternary climatic changes in southern Chile, as recorded in a diatom sequence of Lago Puyehue (40°40′ S)     

Mieke Sterken  Elie Verleyen  Koen Sabbe  Griet Terryn  Francois Charlet  Sébastien Bertrand  Xavier Boës  Nathalie Fagel  Marc De Batist  Wim Vyverman 《Journal of Paleolimnology》2008,39(2):219-235

A late Quaternary diatom stratigraphy of Lago Puyehue (40°40′ S, 72°28′ W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The diatom assemblages were well preserved in a 1,122 cm long, ¹⁴C-dated sediment core spanning the last 17,900 years, and were in support of an early deglaciation of Lago Puyehue. The presence of a short cold spell in South Chile, equivalent to the Younger Dryas event in the Northern Hemisphere, the Antarctic Cold Reversal in Antarctica, or the Huelmo-Mascardi event in southern South America, was not clearly evidenced in the diatom data, although some climate instability may have occurred between 13,400 and 11,700 cal. yr. BP, and a relatively long period (between 16,850 and 12,810 cal. yr. BP) with low absolute abundances and biovolumes could be tentatively interpreted as a period of low rainfall and/or temperatures. An increase in the moisture supply to the lake was tentatively inferred at 12,810 cal. yr. BP. After 9,550 cal. yr. BP, inferred stronger and longer persisting summer stratification, may have been the result of the higher temperatures associated with an early-Holocene thermal optimum. The mid-Holocene appeared to be characterized by a decrease in precipitation, culminating around 5,000 cal. yr. BP, and rising again after 3,000 cal. yr. BP, likely associated with a previously documented lowered frequency and amplitude of El Niño events. An increase in precipitation during the late Holocene (3,000 cal. yr. BP–present) might have marked subsequent increased frequency of El Niño occurrences, leading to drier summers and slightly moister winters in the area.  相似文献   

Climate oscillations evidenced by spectral analysis of Southern Chilean lacustrine sediments: the assessment of ENSO over the last 600 years     

N. Fagel  X. Boës  M. F. Loutre 《Journal of Paleolimnology》2008,39(2):253-266

The Chilean Lake District (38–42°S) is strongly influenced by Southern westerlies-driven precipitations. At 40°S Lago Puyehue provides high resolution sedimentation rates (∼1–2 mm/yr) suitable for annual climate reconstruction. Several short and long sediment cores were collected in this lake. Their analysis aim at a better understanding of climate mechanisms related to ENSO in this part of the world. The recognition of ENSO related periodicities and their stability is studied through the analysis of two short varved cores collected from underflow and interflow key sites. According to varve chronology controlled by ¹³⁷Cs and ²¹⁰Pb profiles and chronostratigraphical markers, the short core from underflow site (PU-I) spans 294 ± 18 years and the core in the interflow site (PU-II) covers 592 ± 9 years. Several methods of spectral analysis were applied on the total varve thickness to identify potential periodicities in the signal. Blackman–Tuckey, Maximum Entropy, Multi-Taper Methods (MTM) and singular spectrum analysis were applied on the whole record. In addition, evolutive MTM and wavelet analyses allow to identify temporal influence of some periodicities. In the PU-I studied interval (AD 1700–2000), a period at ∼3.0 years appears in a large part of the interval, mostly in the recent part. Periods at ∼5.2 and ∼23 years also show up. PU-II record (AD 1400–2000) displays the most robust periodicities at around 15, 9, 4.4, 3.2 and 2.4 years. These periodicities are in good agreement with the sub-decadal periods identified by Dean and Kemp (2004) and linked to the El Nino Southern Oscillation and the Pacific Decadal Oscillation. Differences in the recorded periodicities between PU-I and PU-II sites are consistent with different sedimentation processes in the lake. According to climate instrumental data for the last 20 years, varves in PU-I site are mostly related to fluvial dynamics and regional climate factors, i.e., precipitation, temperature and wind. In PU-II site, varves increment is related to both regional and global climate forcing factors, i.e., El Nino Southern Oscillation. The evolutive MTM analysis and the wavelet analysis suggest a striking break in the periodicities at around AD 1820. Finally relationships between El Nino and longer term climate phase like the Little Ice Age (LIA) are also assessed. This is the seventh in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre and E. Chapron.  相似文献   

Bedload tracing in a high‐sediment‐load mountain stream     

Frédéric Liébault  Hervé Bellot  Margot Chapuis  Sébastien Klotz  Michaël Deschâtres 《地球表面变化过程与地形》2012,37(4):385-399

This paper reports a radiofrequency identification (RFID) tracing experiment implemented in a high‐sediment‐load mountain stream typical of alpine gravel‐bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in southeast France that drains a 38·9‐km² degraded catchment. In spring 2008, we deployed 451 tracers with b‐axis ranging from 23 to 520 mm. Tracers were seeded along eight cross‐sections located in the upstream part of the lowest 2·3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only three months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2·3‐km study reach three years after the onset of the tracing experiment. Travel distances were characterized by right‐skewed and heavy‐tailed distributions, correctly fitted by a power‐law function. This supports the idea that in gravel‐bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low‐flow channel were characterized by a 15‐ to 30‐fold increase of mobility compared to tracers deployed in gravel bars. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Records of large earthquakes in lake sediments along the North Anatolian Fault,Turkey     

X. Boës  S. B. Moran  J. King  M. N. Cağatay  A. Hubert-Ferrari 《Journal of Paleolimnology》2010,43(4):901-920

In 1999, the large surface-rupturing earthquakes of Izmit and Duzce completed a 60-year cycle that included a westward migration of nine consecutive large earthquake failures (>50 km surface rupture), which started with the 1939 Erzincan earthquake in eastern Turkey. In this study, we focused on seismic cycles and seismic risk predictability along the North Anatolian Fault (NAF). Toward the west end of the NAF (26°E–32°E, i.e. Bolu), large earthquake frequency is measured from either historic earthquake catalogs, or geologic records from isolated outcrops and marine sediment cores from the Marmara Sea. In comparison, the eastern part of the NAF zone (32°E–42°E) is less well documented by palaeo-seismologic archives. Thus, the sediment records of lake basins located on the eastern NAF zone constitute a unique opportunity for testing a new palaeo-seismologic approach. To this end, we used a diverse array of complementary methods involving: (1) a 600-km transect of fault-related lakes, (2) sedimentologic observations on cores from six lakes, and (3) a comparison between records of catastrophic sediment transfers in lakes (i.e. radionuclide chronomarkers and erosion tracers) and historic earthquake reports. Our study indicates that lakes along the NAF are sensitive geologic recorders of large surface-rupturing earthquakes (surface-wave magnitude (M _s) ≥ 6.9); smaller intensities are not recorded. The most responsive lake systems exhibit increases in sediment accumulation by a factor of >40 for a >3-m strike-slip displacement (M _s ≥ 7). However, based on results from the 1939 Erzincan earthquake (M _s = 7.8) chronostratigraphic marker, large surface-rupturing earthquakes are detected only by certain lake records and not by others. Matching multiple lake records along the NAF provides information both on the location of a surface rupture of a paleo-earthquake as well as its magnitude. Finally, the shallow lake basins along the NAF could potentially document cycles of large seismic events for at least the late Holocene.  相似文献   

Characterising the origin,nature and fate of sediment exported from catchments perturbed by active tectonics   总被引：1，自引：1，他引：0  

Alexander C. Whittaker  Mikaël Attal  Philip A. Allen 《Basin Research》2010,22(6):809-828

Changes to the tectonic boundary conditions governing erosional dynamics in upland catchments have a significant effect on the nature and magnitude of sediment supply to neighbouring basins. While these links have been explored in detail by numerical models of landscape evolution, there has been relatively little work to quantify the timing, characteristics and locus of sediment release from upland catchments in response to changing tectonic boundary conditions that are well‐constrained independently. We address this challenge by quantifying the volume and granulometric characteristics of sediment exported from modern rivers draining across active normal faults in the Central Apennines in Italy. We demonstrate that catchments undergoing a transient response to tectonics are associated with significant volumetric export of material derived primarily from the zone upstream of the fault, producing bi‐modal grain‐size distributions with elevated D₈₄ values within the transient reach. This is in direct contrast to the headwaters, where the fluvial capacity to transport sediment is low and the grain‐size distribution of material in transit is fine and uni‐modal. The grain‐size response is driven by landslides feeding coarse material directly into the channel, and we show the amplitude of the signal is modulated by the degree of tectonic perturbation, once the threshold for bedrock landsliding is exceeded. Additionally, we evaluate the length‐scale over which this transient grain‐size signal propagates downstream into the basin. We show that the coarse‐fraction sediment released is retained in the proximal hanging‐wall if rates of tectonic subsidence are high and if the axial river system is small or far from the fault‐bounded mountain front. Our results therefore provide some of the first quantitative data to evaluate how transient landscape responses affect the locus, magnitude and calibre of sediment supply to basins.  相似文献   

Topographic reflection of the Socompa debris avalanche,Chile     

Karim Kelfoun  Tim Druitt  Benjamin van Wyk de Vries  Marie-Noëlle Guilbaud 《Bulletin of Volcanology》2008,70(10):1169-1187

One of the most remarkable features of the exceptionally well preserved 26 km³ Socompa debris avalanche deposit is the evidence for topographically driven secondary flow. The avalanche formed by sector collapse of Socompa stratovolcano and spread 40 km across a pre-existing basin, forming a sheet of ∼50 m average thickness. As the avalanche impinged on the western and northern margins of the basin, it was reflected back, forming a secondary flow that continued to travel 15 km down a gentle slope at an oblique angle to the primary flow, the front of the return wave being preserved frozen on the surface of the deposit as a prominent escarpment. Satellite images, aerial photos, digital elevation models and field observations were used to reconstruct the sequence of events during avalanche emplacement, and in particular during secondary flow. The avalanche sheet was divided into distinct terrane groups, each believed to have experienced a particular strain history during emplacement. Evidence for avalanche reflection includes clearly recognizable secondary slide masses, sub-parallel sets of curvilinear shear zones, headwall scarps separating the (primary) levée from the secondary terranes, extensional jigsaw breakup of surface lithologies during return flow, and cross cutting, or deflection, of primary flow fabrics by secondary terranes. Reflection off the basin margin took place in an essentially continuous manner, most major return motions being simultaneous with, or shortly following, primary flow. The secondary flow occurred as a wave that swept obliquely across the primary avalanche direction, remobilizing the primary material, which was first compressed, then stretched, as it passed over and rearward of the wave front. As return flow occurred, surface lithologies were rifted in a brittle manner, and the slabs were sheared pervasively as they glided and rotated back into the basin; some sank into the more fluidal interior of the avalanche, which drained out into a prominent distal lobe. Extension by factors of up to 1.8 took place during return flow. Secondary flow took place on slopes of only a few degrees, and the distal lobe flowed 8 km on a slope of ∼1°. Overall the avalanche is inferred to have slid into place as a fast-moving sheet of fragmental rock debris, with a leading edge and crust with near-normal friction and an almost frictionless, fluidal interior and base. The avalanche emplacement history deduced from field evidence is consistent with the results of a previously published numerical model of the Socompa avalanche.  相似文献   

The ∼AD 1250 effusive eruption of El Metate shield volcano (Michoacán,Mexico): magma source,crustal storage,eruptive dynamics,and lava rheology     

Magdalena Oryaëlle Chevrel  Marie-Noëlle Guilbaud  Claus Siebe 《Bulletin of Volcanology》2016,78(4):32

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Experimental investigation on the grain-scale compression behavior of loose wet granular material     

Than  Vinh-Du  Aimedieu  Patrick  Pereira  Jean-Michel  Roux  Jean-Noël  Tang  Anh Minh 《Acta Geotechnica》2020,15(5):1039-1055

The behavior of model granular materials (glass beads) wetted by a small quantity of liquid forming capillary bridges is studied by one-dimensional compression test combined with X-ray computed tomography (XRCT) observation. Special attention is paid to obtain very loose initial states (initial void ratio of about 2.30) stabilized by capillary cohesion. XRCT-based analyses involve spherical particle detection adapted to relatively low-resolution images, which enable heterogeneities to be visualized and microstructural information to be collected. This study on an ideal material provides an insight into the macroscopic compression behavior of wet granular materials based on the microstructural change, such as pore distance distribution, coordination number of contacts, coordination number of neighbors and number of contacts per grain.

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Multi-objective fitting of concentration-discharge relationships     

José Manuel Tunqui Neira  Vazken Andréassian  Gaëlle Tallec  Jean-Marie Mouchel 《水文研究》2021,35(11):e14428

Concentration–discharge ($C–Q$) relationships are widely used to assess the link between hydrological and biogeochemical processes at the catchment scale. $C–Q$ relationships are mainly calibrated using mono-objective methods to represent, either concentrations or discharge-weighted concentrations (i.e., load). Based on its wide use in hydrological modelling, we test a multi-objective calibration for the $C–Q$ relationship parameters, using both concentration and load, and compare it to a mono-objective calibration applied on either concentrations or load. This work is carried out on a high-frequency dataset (ORACLE-Orgeval Observatory, France). Our findings show that the multi-objective calibration yield a better representation of $C–Q$ relationships parameters during the high and low-flow events. The multi-objective calibration can be used for all forms of $C–Q$ relationships and avoids issues of under-representation of dilution processes characterized by high-discharge, low-concentration periods.  相似文献   

Effect of hot desert weathering on the bulk‐rock iron isotope composition of
L6 and H5 ordinary chondrites     

Gaëlle SAUNIER  Franck POITRASSON  Bertrand MOINE  Michel GREGOIRE  Abdelmadjid SEDDIKI 《Meteoritics & planetary science》2010,45(2):195-209

Abstract– Although iron isotopes are increasingly used for meteorites studies, no attempt has been made to evaluate the effect of terrestrial weathering on this isotopic tracer. We have thus conducted a petrographic, chemical, and iron isotopic study of equilibrated ordinary chondrites (OC) recovered from hot Moroccan and Algerian Saharan deserts environment. As previously noticed, we observe that terrestrial desertic weathering is characterized by the oxidation of Fe‐Ni metal (Fe⁰), sulfide and Fe²⁺ occurring in olivine and pyroxene. It produces Fe‐oxides and oxyhydroxides that partially replace metal, sulfide grains and also fill fractures. The bulk chemical compositions of the ordinary chondrites studied show a strong Sr and Ba enrichment and a S depletion during weathering. Bulk meteoritic iron isotope compositions are well correlated with the degree of weathering and S, Sr, and Ba contents. Most weathered chondrites display the heaviest isotopic composition, by up to 0.1‰, which is of similar magnitude to the isotopic variations resulting from meteorite parent bodies’ formation and evolution. This is probably due to the release of isotopically light Fe²⁺ to waters on the Earth’s surface. Hence, when subtle Fe isotopic effects have to be studied in chondrites, meteorites with weathering grade above W2 should be avoided.  相似文献