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541.
542.
Pedro J. Marenco Frank A. Corsetti David J. Bottjer 《Geochimica et cosmochimica acta》2008,72(6):1570-1582
An integrated stable isotope, elemental and petrographic analysis of Early Triassic (Spathian) carbonates and evaporites along a proximal to deep environmental transect reveals significant variations in δ34S composition of carbonate associated sulfate (CAS). The variations in the δ34S of CAS are strongly correlated with the Ca/Mg composition of carbonates, suggesting that the variations are driven by the degree of dolomitization. The δ34S of dolostones and evaporites are similar to one another and exhibit lower δ34S values than limestones from all localities.Three hypotheses may explain the differences in δ34S between proximal dolostones/evaporites and inner/middle shelf limestones: (1) limestones experienced anaerobic sulfate reduction and subsequent incorporation of 34S-enriched sulfate into CAS during diagenesis, while dolostones did not—this is unlikely because of the lack of correlation between δ34SCAS and TOC, as well as other indicators of diagenesis, (2) dolomitization controlled the δ34SCAS in proximal paleoenvironments, where the source of the 34S depleted fluids was either continentally-derived or the result of Rayleigh distillation during evaporite formation, and (3) a δ34S depth gradient existed during the Early Triassic such that limestones formed in distal waters are more enriched in 34S versus evaporites and dolostones formed in proximal settings—we do not favor this hypothesis because the strong correlation between Ca/Mg and δ34SCAS implies that dolomitization controls the δ34SCAS in these samples. Results from subtidal, well-preserved (non-dolomitized) limestones suggest that the δ34S of Spathian seawater sulfate may have been heavier than previously suggested from analyses of evaporite deposits alone. 相似文献
543.
544.
Summary An integrated pilot paleomagnetic and sedimentological study has been conducted in the Neogene-Quaternary infilling materials of the Bajo Segura Basin (Eastern Betics, SE Spain). The studied sediments belong to the youngest (late Pliocene-Quaternary) lithostratigraphic unit of the basin (P-Q unit). The statistical analysis of tectonic striations and stylolitic dissolutions on the conglomerate limestone clasts indicates a NNW-SSE maximum compression direction. This is in accordance with the principal susceptibility axes, determined from the anisotropy of magnetic susceptibility measurements (AMS) of the interbedded siltstones where the Kmax axis group in a subhorizontal N 080° E direction.A total of 45 core samples have been collected from 16 stratigraphic siltstone levels encompassing the described section at Crevillente with the aim to establish a magnetochronology. Upwards in the section the NRM intensity and bulk susceptibility vary from 10–2 to 10–3 A/m and from 1550 to 100 × 10–6 SI, respectively. The mean characteristic remanent magnetization (ChRM) after bedding correction (Dec/Inc = 10°/60°, 95 = 8.7°, k = 15.9) is deviated slightly towards the E from the reference N direction, and could reflect a deflection related to the observed magnetic fabric although no clear correlation exists with AMS parameters. The derived magnetostratigraphy reveals only one reversal boundary within the upper third of the section, delimiting an upper reversal magnetozone which has been tentatively correlated with the Olduwai subchron close to the Plio-Pleistocene boundary.Pilot and preliminary rock-magnetic experiments and standard X-ray difraction (XRD) analysis have been performed on typical samples in order to establish the carriers of magnetization and characterize the sedimentological and magnetic-acquisition processes in these sediments. Magnetic carriers seem to be dominated by magnetite with a relative grain size within the PSD state (pseudo single-domain) threshold, but closer to the MD (multi domain) threshold, which favours the detrital origin for the magnetite. 相似文献
545.
Juan Pablo Lovecchio Sébastien Rohais Philippe Joseph Néstor D. Bolatti Pedro R. Kress Ricardo Gerster Víctor A. Ramos 《地学学报》2018,30(5):359-368
The identification of three independent rifting events in the Colorado basin area highlights the complexity of its Mesozoic rifting history, which ended in the Early Cretaceous with the opening of the South Atlantic Ocean. A first rifting event, associated with the extensional reactivation of previously compressive thrusts of the Ventania‐Cape fold belt, is transected by faults forming the main depocenters of the Colorado and possibly the adjacent Salado basin. The second and main rifting stage is correlated with the Early Jurassic Karoo rifting. In the Early Cretaceous, WNW–ESE extension produced NNE‐trending landward‐dipping faults, concentrated in the outer 100–200 km of the continental crust domain, possibly coeval with SDR emplacement. This is the first identification of three superimposed rifting settings in the southern South Atlantic realm and is key to understanding the complex Mesozoic breakup history of SW Gondwana. 相似文献
546.
Pedro Rau Luc Bourrel David Labat Denis Ruelland Frdric Frappart Waldo Lavado Boris Dewitte Oscar Felipe 《水文研究》2019,33(1):20-35
In a context of water scarcity in Peruvian Pacific catchments as a crucial issue for Peru, added to the paucity of data availability, we propose a methodology that provides new perspectives for freshwater availability estimation as a base reference for unimpaired conditions. Under those considerations, a regional discharge of 709 m3/s to the Pacific Ocean is estimated with a significant increasing trend of about 43 m3/s per decade over the 1970 – 2010 period. To represent the multidecadal behaviour of freshwater runoff along the region, a regional runoff analysis is proposed based on hydrological modelling at annual and monthly time step for unimpaired conditions over the whole 1970 – 2010 period. Differential Split‐Sample Tests are used to assess the hydrological modelling robustness of the GR1A and GR2M conceptual lumped models, showing a satisfactory transposability from dry to wet years inside the thresholds defined for Nash–Sutcliffe and bias criteria. This allowed relating physical catchment characteristics with calibrated and validated model parameters, thus offering a regional perspective for dryland conditions in the study area (e.g., the anticlockwise hysteresis relationship found for seasonal precipitation–runoff relationship) as well as the impacts of climate variability and catchment characteristics. 相似文献
547.
Maurizio M. Chiaramonte Pedro Arduino Dawn E. Lehman Charles W. Roeder 《地震工程与结构动力学》2013,42(10):1435-1450
Marginal wharves are key components in providing functionality of port facilities. Ports are central components of the US economy. Earthquake damage to a port can disrupt the economic stability. Therefore, port facilities must be able to quickly return to full operation shortly after a seismic event. Prior studies have shown that integrity of marginal wharves may be compromised by excessive soil movement and structural damage. The latter is often localized at pile‐to‐wharf connections and in the pile body buried within the soil. Recent research has resulted in an improved connection design that mitigates damage. This study was undertaken to evaluate the full seismic performance of marginal wharves including both conventional and damage‐resisting connections. A series of finite element models of a representative pile‐supported wharf facility were created. The models varied in their moment‐resisting pile‐to‐wharf connections. A total‐stress analysis approach was used to capture the soil response along with p–y, t–z, and Q–z soil–structure interaction springs. Validated connection interface elements were integrated with non‐linear frame elements to simulate the marginal wharf structure and substructure. Non‐linear static pushover and dynamic time history analyses, for three different hazard levels, were performed. The results of the numerical simulations were used to assess the performance of the marginal wharf including estimates of crane damage and port downtime. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
548.
Pedro Fidelman Louisa EvansMichael Fabinyi Simon FoaleJosh Cinner Franciska Rosen 《Marine Policy》2012,36(1):42-53
Environment and development agendas are increasingly being characterised by regional-scale initiatives. This trend is in part motivated by recognition of the need to account for global drivers of change (e.g., climate change, migration, and globalisation), the aspirations of achieving large-scale ecological goals (such as maintaining ecosystem processes), and reconciling potentially conflicting priorities in multi-use planning. However, regional-scale governance is challenging and there is little theoretical guidance or empirical evidence to suggest how it can be achieved. This paper uses the Institutional Analysis and Development framework to highlight the diverse contextual factors that challenge governance of a large-scale marine common, using an example of the Coral Triangle Initiative. The analysis points to the need for a critical, reflexive approach to the Coral Triangle Initiative if it is to effectively navigate diverse contexts and reconcile multiple objectives in the region. Recognising the heterogeneous, multi-scale and interlinked nature of large-scale marine systems is critical. Coping with contextual complexity will require innovative approaches that strive to be inclusive of varied perspectives and actors, enable and support effective collective-choice arrangements at lower levels of organisation, and organise and link diverse institutional arrangements at multiple scales. Large-scale marine governance will also involve a great deal of experimentation and regular adjustments to governance arrangements to account for the dynamic nature of regional commons. 相似文献
549.
This study reports the performance of a combined anaerobic–aerobic packed‐bed reactor that can be used to treat domestic sewage. Initially, a bench‐scale reactor was operated in three experimental phases. In the first phase, the anaerobic reactor was operated with an average organic matter removal efficiency of 77% for a hydraulic retention time (HRT) of 10 h. In the second phase, the reactor was operated with an anaerobic stage followed by an aerobic zone, resulting in a mean value of 91% efficiency. In the third and final phase, the anaerobic–aerobic reactor was operated with recirculation of the effluent of the reactor through the anaerobic zone. The system yielded mean total nitrogen removal percentages of 65 and 75% for recycle ratios (r) of 0.5 and 1.5, respectively, and the chemical oxygen demand (COD) removal efficiencies were higher than 90%. When the pilot‐scale reactor was operated with an HRT of 12 h and r values of 1.5 and 3.0, its performance was similar to that observed in the bench‐scale unit (92% COD removal for r = 3.0). However, the nitrogen removal was lower (55% N removal for r = 3.0) due to problems with the hydrodynamics in the aerobic zone. The anaerobic–aerobic fixed‐bed reactor with recirculation of the liquid phase allows for concomitant carbon and nitrogen removal without adding an exogenous source of electron donors and without requiring any additional alkalinity supplementation. 相似文献
550.
Pedro Walfir M. Souza-Filho Roberto Vizeu L. Pinheiro Francisco R. Costa José Tasso F. Guimarães Prafulla K. Sahoo Marcio S. Silva Cleverson G. Silva 《地球表面变化过程与地形》2020,45(14):3732-3746
This work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho-structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion by – and building of – the formation of the South Carajás Hill; (iii) Fe-rich crust formation by weathering and gravitational collapse faults following the E–W plateau border and the start of Violão Lake formation during the Pliocene–Pleistocene; and (iv) episodic fault-fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake-level fluctuations. Initial fault reactivation under low-level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine-grained sediments from dilute interflows or overflows until 36 000 cal year BP. At about 31 000 cal year BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation. © 2020 John Wiley & Sons, Ltd. 相似文献