Palaeomagnetism and magnetostratigraphy of uppermost Permian strata, southeast New Mexico, USA: correlation of the Permian–Triassic boundary in non-marine environments     

Roberto S. Molina Garza  John W. Geissman  & Spencer G. Lucas 《Geophysical Journal International》2000,141(3):778-786

Continental red sandstone and siltstone rocks of the Dewey Lake (Quartermaster) Formation at Maroon Cliffs, near Carlsbad, New Mexico, are characterized by two components of magnetization with partially overlapping laboratory unblocking temperature spectra. Both magnetizations display high coercivities (>100 mT), probably residing in haematite. A north-directed magnetization with steep positive inclination unblocks between 100 and 650 °C, isolating a predominantly northwest-directed magnetization, with shallow inclination, of near uniform normal polarity and maximum unblocking temperatures of 680 °C.
We collected samples from 24 palaeomagnetic sites (i.e. individual beds) from a ~60 m thick section of flat-lying strata disconformably overlying carbonate and evaporite rocks of the Rustler Formation. The upper member of the Rustler Formation contains a Late Permian (early Changxingian) marine invertebrate and conodont fauna. Of the sampled sites, four yield only steep magnetizations, interpreted to be recent overprints. Eight sites did not yield well-grouped site means and were excluded from the final calculations. The formation mean (dec = 337.7°, inc = 9.2°; k = 31.6, α ₉₅ = 7.8°, N = 12 sites) defines a palaeomagnetic pole located at 55.2°N, 117.5°E, in good agreement with other Late Permian North American cratonic poles.
Correlation of the short polarity sequence of this section of Dewey Lake strata is unambiguous. Compared with the polarity stratigraphy of marine sections in Asia, and supported by isotopic age determinations on a widespread bentonite bed in Dewey Lake strata in west Texas (approximately 251 Ma) and fossil data for the underlying Rustler Formation, the magnetostratigraphy is consistent with deposition of the Dewey Lake Formation during the latest Changxingian (Late Permian) stage.  相似文献   

Subglacial drumlins and englacial fractures at the surge-type glacier,Múlajökull,Iceland     

Andrew Finlayson  Emrys Phillips  Ívar Örn Benediktsson  Lucas K. Zoet  Neal R. Iverson  Jez Everest 《地球表面变化过程与地形》2019,44(1):367-380

The interaction between drumlins and overriding glacier ice is not well studied, largely due to the difficulty of identifying and accessing suitable active subglacial environments. The surge-type glacier Múlajökull, in central Iceland, overlies a known field of actively forming drumlins and therefore provides a rare opportunity to investigate the englacial structures that have developed in association with ice flow over the subglacial drumlins. In this study detailed ground-penetrating radar surveys are combined with field observations to identify clear sets of up-glacier and down-glacier dipping fractures at Múlajökull's margin. These are interpreted as conjugate shear planes or P- and R-type Reidel shears that developed and filled with saturated sediment derived from the glacier bed, during a previous surge. The fracture sets exhibit focused spatial distributions that are influenced by the subglacial topography. In particular, down-glacier dipping fractures are strongly focused over drumlin stoss slopes. These fractures, although well developed at depth, were mostly unable to transmit basal water and sediment up to the glacier surface during the surge cycle. In contrast, up-glacier dipping fractures formed over drumlin lee sides and in more gently sloping swales, and more frequently connected to the glacier surface, providing a pathway for the evacuation of basal water and water-saturated sediment. The study suggests that the subglacial drumlins under Múlajökull's margin have influenced the nature and distribution of englacial fractures, which could potentially contribute to spatial variations in basal water pressure during a surge. BGS © UKRI 2018  相似文献   

Protracted river response to medieval earthquakes     

Amelie Stolle  Wolfgang Schwanghart  Christoff Andermann  Anne Bernhardt  Monique Fort  John D. Jansen  Hella Wittmann  Silke Merchel  Georg Rugel  Basanta Raj Adhikari  Oliver Korup 《地球表面变化过程与地形》2019,44(1):331-341

Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from seismic disturbances, depending on how recovery is defined. We examine three principal proxies of river recovery after earthquake-induced sediment pulses around Pokhara, Nepal's second largest city. Freshly exhumed cohorts of floodplain trees in growth position indicate rapid and pulsed sedimentation that formed a fan covering 150 km² in a Lesser Himalayan basin with tens of metres of debris between the 11th and 15th centuries AD. Radiocarbon dates of buried trees are consistent with those of nearby valley deposits linked to major medieval earthquakes, such that we can estimate average rates of re-incision since. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos, and dated tree trunks to reconstruct geomorphic marker surfaces. The volumes of sediment relative to these surfaces require average net sediment yields of up to 4200 t km^–2 yr^–1 for the 650 years since the last inferred earthquake-triggered sediment pulse. The lithological composition of channel bedload differs from that of local bedrock, confirming that rivers are still mostly evacuating medieval valley fills, locally incising at rates of up to 0.2 m yr^–1. Pronounced knickpoints and epigenetic gorges at tributary junctions further illustrate the protracted fluvial response; only the distal portions of the earthquake-derived sediment wedges have been cut to near their base. Our results challenge the notion that mountain rivers recover speedily from earthquakes within years to decades. The valley fills around Pokhara show that even highly erosive Himalayan rivers may need more than several centuries to adjust to catastrophic perturbations. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in active mountain regions. © 2018 John Wiley & Sons, Ltd.  相似文献   

Comparative reproductive biology of two southwestern Atlantic populations of the hermit crab Pagurus exilis (Crustacea: Anomura: Paguridae)     

Mariana Terossi  Lucas S. Torati  Ivana Miranda  Marcelo A. Scelzo  Fernando L. Mantelatto 《Marine Ecology》2010,31(4):584-591

Pagurus exilis (Benedict, 1892) is an endemic South Atlantic hermit crab with a distribution ranging from Rio de Janeiro State, Brazil, to Buenos Aires Province, Argentina. The present study analyzed the reproduction of two populations at the extremes of this geographical distribution, and compared their reproductive period, fecundity, and changes in egg size and egg volume during the incubation period in order to assess the variability over this latitudinal range. Hermit crabs were collected monthly over a 2‐year period. In total, 108 females were analyzed for Brazil (44 non‐ovigerous and 64 ovigerous), and 141 for Argentina (87 non‐ovigerous and 54 ovigerous). Reproduction in Brazil occurs year‐round, with peaks in the fall and winter seasons; in Argentina reproduction occurs only in spring and summer. The Brazilian ovigerous females were significantly larger than the Argentina ones (Brazil: SL = 5.33 ± 1.45 mm; Argentina: SL = 4.15 ± 0.52 mm; P < 0.001). The fecundity was 1447 ± 831 eggs (317 to 2885) in Brazil and 987 ± 711 eggs (114 to 2665) in Argentina, with a trend towards higher fecundity in Brazil. Eggs in the Argentina population were larger than those in Brazil for all the three stages investigated, and no changes in egg volume were found during egg development for both populations. The reproductive traits of the two populations showed some important differences, which may reflect adaptations to local environmental conditions, demonstrating a high plasticity of reproductive features of the species in Brazilian and Argentine waters. The strategy adopted by the Argentina population involves a lower production of larger eggs compared to the population in Brazil; this lower production is associated with reproduction in cold‐water regions.  相似文献   

A multidisciplinary study of the Cape Peloro brackish area (Messina, Italy): characterisation of trophic conditions, microbial abundances and activities     

Marcella Leonardi  Filippo Azzaro  Maurizio Azzaro  Gabriella Caruso  Monique Mancuso  Luis Salvador Monticelli  Giovana Maimone  Rosabruna La Ferla  Francesco Raffa  & Renata Zaccone 《Marine Ecology》2009,30(S1):33-42

In the framework of the VECTOR DIVCOST Project, a 2-year investigation was started in 2006, with the aim of testing the sensibility of microbial parameters to environmental changes and of assessing whether they can provide information about functional changes in the carbon cycle. The investigation was performed in the surface waters of two small brackish ponds (Ganzirri and Faro), located in the Cape Peloro transitional area (Sicily, Italy). The seasonal changes in both the microbial compartment [bacterioplankton, vibrios, exoenzymatic hydrolysis of proteins and polysaccharides, bacterial secondary production (HBP) and community respiration] and the trophic state of suspended matter [total suspended matter (TSM), particulate organic carbon (POC), particulate organic nitrogen (PON), C/N] were analysed in relation to the hydrological characteristics [temperature, salinity, oxygen, fluorescence, NH₄, NO₂, NO₃, PO₄]. Despite marked differences in the nutritional input and the diversification in both carbon budget and trophic level, the two ponds show similar trends in many of the investigated factors, hardly influenced by seasonal variations. Temporally coupled trends were observed for some parameters (enzyme activities, vibrios abundances, respiratory activity), whereas others (POC, PON, heterotrophic bacterial production, bacterioplankton) showed a seasonal shift between the two lakes. The different behaviour found for the some biotic parameters suggests that their response to environmental conditions may be modulated differently between the two lakes, which, despite their spatial proximity and reciprocal connection, do not always show contemporaneous functional processes.  相似文献   

Tracing of dissolved organic matter from the Sepetiba Bay (Brazil) by PARAFAC analysis of total luminescence matrices   总被引：2，自引：0，他引：2  

Luciani X  Mounier S  Paraquetti HH  Redon R  Lucas Y  Bois A  Lacerda LD  Raynaud M  Ripert M 《Marine environmental research》2008,65(2):148-157

Fluorescent excitation-emission matrices (FEEM) of the fluorescent dissolved organic matter (FDOM) are widely used for DOM characterization and tracing. In this work, a set of FEEM from sampling campaigns in the Sepetiba Bay (Brazil) was decomposed into independent components using the parallel factor analysis (PARAFAC) algorithm. Four independent components were extracted describing the total fluorescence of the FDOM. The well described peaks A, C, M, B and T were found, and a new peak, A', linked to the C peak, was detected. Relative contribution of each of four components to the total fluorescence confirms that the coastal water has DOM of terrestrial origin, except for the 275Ex/400-500Em range (nm), which primarily occurs in marine waters.  相似文献   

Mineralogy and Geochemistry of Rural Road Dust and Nearby Mine Tailings: A Case of Ignored Pollution Hazard from an Abandoned Mining Site in Semi-arid Zone     

Del Rio-Salas  Rafael  Ayala-Ramírez  Yessi  Loredo-Portales  René  Romero  Francisco  Molina-Freaner  Francisco  Minjarez-Osorio  Christian  Pi-Puig  Teresa  Ochoa–Landín  Lucas  Moreno-Rodríguez  Verónica 《Natural Resources Research》2019,28(4):1485-1503

Natural Resources Research - Abandoned mine tailings are considered as one of the main sources of potentially toxic elements. Because of the lack of supervision, particularly from small-scale or...  相似文献   

Towards semantic‐aware multiple‐aspect trajectory similarity measuring     

Lucas May Petry  Carlos Andres Ferrero  Luis Otavio Alvares  Chiara Renso  Vania Bogorny 《Transactions in GIS》2019,23(5):960-975

The large amount of semantically rich mobility data becoming available in the era of big data has led to a need for new trajectory similarity measures. In the context of multiple‐aspect trajectories, where mobility data are enriched with several semantic dimensions, current state‐of‐the‐art approaches present some limitations concerning the relationships between attributes and their semantics. Existing works are either too strict, requiring a match on all attributes, or too flexible, considering all attributes as independent. In this article we propose MUITAS, a novel similarity measure for a new type of trajectory data with heterogeneous semantic dimensions, which takes into account the semantic relationship between attributes, thus filling the gap of the current trajectory similarity methods. We evaluate MUITAS over two real datasets of multiple‐aspect social media and GPS trajectories. With precision at recall and clustering techniques, we show that MUITAS is the most robust measure for multiple‐aspect trajectories.  相似文献   

Progress towards instrument miniaturisation for mid-IR long-baseline interferometry     

Lucas Labadie  Stefano Minardi  Guillermo Martín  Robert R. Thomson 《Experimental Astronomy》2018,46(3):433-445

We report recent results on passive mid-infrared integrated optics from the project “Advanced Laser-writing for Stellar Interferometry” and shortly describe the perspectives of their hybridisation with active components for the benefit of the spectro-interferometry technique.  相似文献   

Input Selection Based on Information Theory for Constructing Predictor Models of Solar and Geomagnetic Activity Indices     

Mohammadmahdi Rezaei Yousefi  Babak Salehi Kasmaei  Abdolhossein Vahabie  Caro Lucas  Babak Nadjar Araabi 《Solar physics》2009,258(2):297-318

Various phenomena with solar origin and their mutual dependence must be studied in order to predict behaviors in solar – terrestrial system. Linear statistical methods prevalent in analyzing natural systems may not be able to detect nonlinear dependencies among solar and geomagnetic processes. When relations, whether linear or nonlinear, between indices and their changes over time are revealed, better predictions can be made through appropriate modeling techniques. Selection of nonredundant input variables to build suitable models for prediction of solar and geomagnetic activity is of utmost importance. Mutual information is a tool that is capable of capturing all dependencies for detecting nonlinear relations and selecting the best subset of input variables by means of an applicable algorithm that maximizes information about the output and minimizes the shared information between inputs. High generalization power and improved interpretability of the selected inputs are the consequences of this analysis.  相似文献