Characterisation of a Pleistocene debris-avalanche deposit in the Tenteniguada Basin,Gran Canaria Island,Spain     

Alejandro Lomoschitz  Javier Hervás  Jorge Yepes  Joaquín Meco 《Landslides》2008,5(2):227-234

We studied a large debris-avalanche deposit of Pleistocene age in the Tenteniguada Basin, Gran Canaria Island, Spain. This deposit, which is well preserved because it is mostly covered by basanite lava flows, has distinctive matrix and block facies, hummocky topography and internal structures typical of debris avalanches. However, neither syneruptive lavas nor some characteristic features of volcanic debris-avalanche deposits, such as a stratovolcano edifice or a horseshoe-shaped crater, are present. The occurrence of internal features characteristic of volcanic avalanche deposits could be attributed to the volcanic materials involved in the movement rather than to the triggering of the avalanche during a volcanic eruption. The conditioning factors are shown to be associated with specific structural and hydrological conditions, such as the presence of old volcanic domes, strength reduction of the rocks, effective stress decrease, active gully erosion and water table rise during Pleistocene humid episodes. We finally suggest that the possible triggering factor of the avalanche was a neighbouring volcanic or tectonic earthquake.  相似文献   

Diatom species variation between lake habitats: implications for interpretation of paleolimnological records     

Sergi Pla-Rabés  Jordi Catalan 《Journal of Paleolimnology》2018,60(2):169-187

A sample of a sediment record contains diatom species that have grown in disparate habitats and eventually accumulated in a deep part of the lake. The original habitats may differ in substrate, depth location, and availability of resources. Identifying the species characteristic of each habitat should improve our ecological and environmental interpretation of the sediment record by distinguishing habitat specific responses. With this aim, we studied the benthic diatom communities of a deep oligotrophic lake across several habitats. The main source of variation in the diatom composition was the substrate type; particularly, sediment biofilms. Depth was the second factor. The thermocline defined a shift in diatom communities that also included changes in the dominant lifeforms. A third factor was the mesoscale heterogeneity (i.e., rock sides). Although most species were present in many habitats, characteristic species were identified for all the main habitats and used for an improved interpretation of the deep sediment record. Appropriate standardization showed increasing species richness and diversity from epilimnetic epilithic samples to hypolimnetic sediment samples. We estimate that more than 5000 valve counts are required for appropriate comparisons. Consequently, in sediment records with lower counts per sample, one has to amalgamate samples—losing temporal resolution—to achieve reliable analyses of diversity changes over time. Deep sediment samples are representative of the gamma-diversity of the lake diatom metacommunity, which result from the local alpha diversity of the habitats and the beta-diversity of the variability in composition among them. This double source of diversity has to be taken into account when using the sediment record for estimating lake biodiversity changes. On the other hand, we show that an estimation of the spatial (habitat) heterogeneity of a reconstructed environmental variable can be achieved using subsets of species characteristic of each habitat. We demonstrate the procedure by reconstructing the pH fluctuations during the last 200 years in several habitats from a single sediment record. The results are coherent with the expected differences between predominantly trophogenic or tropholithic habitats.  相似文献   

Hyperspectral core logging for fire reconstruction studies     

Antonin Van Exem  Maxime Debret  Yoann Copard  Boris Vannière  Pierre Sabatier  Stephane Marcotte  Benoit Laignel  Jean-Louis Reyss  Marc Desmet 《Journal of Paleolimnology》2018,59(3):297-308

Lacustrine sediments contain a wide range of proxies that enable paleoenvironmental reconstructions. For instance, charcoal can be used to document past fire regime changes. In order to analyse high-temporal- and spatial-resolution records, however, it is necessary to develop fast, low-cost and high-stratigraphic-resolution methods. We developed a new paleo-fire proxy by studying a lacustrine core from the Esterel Massif, SE France, an area affected by two recent fire events, in AD 1987 and 2003. For this purpose, we searched for charcoal deposited and preserved in the lake sediments by combining a number of complementary methods, including: classic macrocharcoal tallying, scanning spectrophotometry, scanning hyperspectral imaging and high pressure liquid chromatography analyses. Macrocharcoal quantification is efficient, but time-consuming, and only provides intermediate-resolution data (cm scale). Spectrophotometry, used classically to quantify colour, is very fast, provides high-resolution data (4 mm) and is non-destructive (core preservation). Hyperspectral data have the same advantages as spectrophotometry, but offer higher spatial resolution (64-µm pixel size) and higher spectral resolution (6 nm) for core logging applications. The main result of this research is based on hyperspectral analysis at very high stratigraphic resolution using the I-band index. This index usually measures reflectance values at [660, 670 nm] corresponding to the trough in red reflectance produced by Chlorophyll a and its diagenetic products. This [660, 670 nm] reflectance trough, however, is also affected by the presence of altered organic matter and decreases with altered organic matter such as charcoal particles. Charcoal effect on the reflectance of Chlorophyll a and its diagenetic products is identified on first derivative spectra by a characteristic pattern around 675 nm, which is also in agreement with the Chlorophyll a concentrations measured by high-pressure liquid chromatography and charcoal particles. The I-band index is hence suitable for detecting burned organic matter, by quantifying the dilution of the chlorophyll signal by the charcoal signal. Thus, this adaptation of the I-band index can be applied in fire reconstruction studies.  相似文献   

From platform to basin to swell: orbital control on sedimentary sequences in the Oxfordian, Spain     

André Strasser  Marc Aurell  Beatriz Bádenas  Guillermo Meléndez  Sara Tomás 《地学学报》2005,17(5):407-413

Climatic, oceanographic and ecological changes that control the formation and deposition of sediment in shallow and deep depositional environments commonly occur with periodicities of a few 10 000 years. Consequently, in order to interpret sedimentary sequences in the geological past, high time resolution is required. This is best obtained by cyclostratigraphy. Three sections have been studied in the Oxfordian of north-eastern Spain: one represents a shallow, siliciclastic-carbonate platform with repetitive subaerial exposures, one an intraplatform basin with sponge bioherms, and one a swell where iron ooids and glauconite formed. The platform section displays a well-defined stacking pattern of depositional sequences; the deeper-water sections are well dated by ammonites. The correlation between the three sections is a best-fit solution integrating biostratigraphy, sequence stratigraphy and cyclostratigraphy. It is concluded that the small-scale depositional sequences formed in tune with the 100-ka orbital eccentricity cycle. An additional factor was differential subsidence that ruled basin morphology.  相似文献   

Dynamics of perfect fluid unified dark energy models     

Luís M. G. Beça  Pedro P. Avelino 《Monthly notices of the Royal Astronomical Society》2007,376(3):1169-1172

  相似文献   

The HIPPARCOS input catalogue: A progress report from an astrometric point of view     

Y. Réquième  C. Turon 《Astrophysics and Space Science》1991,177(1-2):115-119

  相似文献   

An application of the combined conglomerate-fold test to the study of foreland basins. Palaeomagnetic results from the southeastern Ebro Basin     

J. M. Parés 《Geophysical Journal International》1989,99(1):223-228

  相似文献   

A very cool brown dwarf in UKIDSS DR1     

S. J. Warren  D. J. Mortlock  S. K. Leggett  D. J. Pinfield  D. Homeier  S. Dye  R. F. Jameson  N. Lodieu  P. W. Lucas  A. J. Adamson  F. Allard  D. Barrado y Navascués  M. Casali  K. Chiu  N. C. Hambly  P. C. Hewett  P. Hirst  M. J. Irwin  A. Lawrence  M. C. Liu †  E. L. Martín  R. L. Smart  L. Valdivielso  B. P. Venemans 《Monthly notices of the Royal Astronomical Society》2007,381(4):1400-1412

  相似文献   

The role of syn-eruptive vesiculation on explosive basaltic activity at Mt. Etna,Italy     

Margherita Polacci  Michael R. Burton  Alessandro La Spina  Filippo Murè  Stefano Favretto  Franco Zanini 《Journal of Volcanology and Geothermal Research》2009,179(3-4):265-269

We investigated the dynamics of explosive activity at Mt. Etna between 31 August and 15 December 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active, summit crater. The analysed scoria clasts present large, connected vesicles with complex shapes and smaller, isolated, spherical vesicles, the content of which increases in scoriae from the most explosive events. Gas geochemistry reports CO₂/SO₂ and SO₂/HCl ratios supporting a deep-derived gas phase for fire-fountain activity. By integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of Mt. Etna activity in 2006 were driven by a previously accumulated CO₂-rich gas phase but we highlight the lesser role of syn-eruptive vesicle nucleation driven by water exsolution during ascent. We conclude that syn-eruptive vesiculation is a common process in Etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation.  相似文献   

A rapid method to map the crustal and lithospheric thickness using elevation, geoid anomaly and thermal analysis. Application to the Gibraltar Arc System, Atlas Mountains and adjacent zones   总被引：1，自引：0，他引：1  

J. Fullea  M. Fernndez  H. Zeyen  J. Vergs 《Tectonophysics》2007,430(1-4):97-117

We present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness. The main assumptions are local isostasy and a four-layered model composed of crust, lithospheric mantle, sea water and the asthenosphere. We consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle. We perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of RMS error of elevation and geoid anomaly databases. The application of this method to the Gibraltar Arc System, Atlas Mountains and adjacent zones reveals the presence of a lithospheric thinning zone, SW–NE oriented. This zone affects the High and Middle Atlas and extends from the Canary Islands to the eastern Alboran Basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz. A number of different, even mutually opposite, geodynamic models have been proposed to explain the origin and evolution of the study area. Our results suggest that a plausible slab-retreating model should incorporate tear and asymmetric roll-back of the subducting slab to fit the present-day observed lithosphere geometry. In this context, the lithospheric thinning would be caused by lateral asthenospheric flow. An alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe.  相似文献