Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation,Ischigualasto Provincial Park,San Juan,Argentina     

Brian S. Currie  Carina E. Colombi  Neil J. Tabor  Todd C. Shipman  Isabel P. Montañez 《Journal of South American Earth Sciences》2009,27(1):74-87

The Ischigualasto Formation in northwestern Argentina contains abundant fluvial channel sandstones, overbank mudstones, and paleosols that were deposited in a northwest-trending continental-rift basin during Late Triassic time. In the study area the formation progressively thins from ～700 m in the west to ～400 m in the east, over a distance of 7 km. This thinning is accompanied by a relative decrease in the abundance of fluvial channel sandstones and an increase in mud-rich overbank deposits and paleosols. While preserved channel deposits in the formation are highly variable in terms of their size and stratigraphic distribution, four general channel forms can be recognized based on their overall cross sectional geometry and internal sedimentary structures. Of these, the dominant channel-body types are interpreted as the deposits of sandy multi-channel fluvial systems. The internal stratigraphic architecture of the Ischigualasto Formation indicates that during deposition, the central part of the basin was the location of a long-lived, north flowing, fluvial channel belt that received relatively continuous channel and proximal overbank deposition. To the east, however, channel-related deposition was more infrequent, resulting in enhanced pedogenic modification of alluvial deposits. The overall thickness and facies trends observed in the Ischigualasto Formation most likely correspond to variations in fault-related accommodation development within the basin during the time of deposition.  相似文献   

Modelling the cross-shore profiles of sand beaches using artificial neural networks     

Isabel López  Luis Aragonés  Yolanda Villacampa 《Marine Georesources & Geotechnology》2013,31(6):683-694

Abstract

Artificial neural networks (ANN) have been widely used successfully to solve coastal engineering problems. In this article, they are used to model the cross-shore profile of sandy beaches taking into account the possible effect of marine vegetation (Posidonia oceanica). Sixty ANNs were generated by modifying both the inputs and the number of neurons in the hidden layer. The best results were obtained with the following inputs: wave height perpendicular to the coast and the associated period and probability of occurrence, median sediment size, profile slope, and energy reduction factor due to P. oceanica. With these inputs and 10 neurons in the hidden layer, a mean absolute error of 0.22?m during training and 0.21?m during the test was obtained, which represents an improvement of 81.2% and 55.5% compared to models without and with P. oceanica.  相似文献   

Late Holocene history of the floodplain lakes of the Cauca River, Colombia     

Maria Isabel Velez  Jose Ignacio Martínez  Fiore Suter 《Journal of Paleolimnology》2013,49(4):591-604

We conducted a paleolimnological investigation of late Holocene deposits on a distal, constrained floodplain of the Cauca River, northern Colombia, i.e. the La Caimana sedimentary succession. The record starts sometime between 4,500 and 4,000 cal yr BP, when the first high-energy fluvial events inundated an ancient soil surface. From that time until about 3,260 cal yr BP, a stable and probably seasonal flooding regime was established on the floodplain. From ~3,260 to ~2,800 cal yr BP, ephemeral and shallow swamps developed on the floodplain. Their formation and duration depended on their connection with the Cauca River. From ~2,800 to ~2,400 cal yr BP, fluvial influence became more dominant, establishing a semi-permanent connection between the river and the floodplain. From ~2,400 to 1,400 cal yr BP, episodic formation of ephemeral swamps occurred. During this stage, floodplain lakes displayed high salinity and nutrient concentrations, and possibly alkaline conditions as a consequence of reduced water volume when the connection with the river was reduced or lost completely. A change in the hydrological regime occurred from ~1,400 to ~850 cal yr BP, when high-energy fluvial events were punctuated by periods of reduced flooding that enabled soil formation. Generally, connection with the Cauca River resulted in lake waters with low salinity and nutrient concentration, whereas loss of connection with the river led to lakes with greater salinity and nutrient content. Paleocurrent analyses indicate that flows came predominantly from the Cauca River, suggesting the lakes were formed by the impoundment of La Caimana Creek. The sedimentary succession of La Caimana offers a unique, high-resolution record of the evolution and dynamics of an ancient floodplain of the Cauca River and its aquatic ecosystems.  相似文献   

The definition of potential infiltration areas in Guaratinguetá watershed, Paraíba do Sul Basin, Southeastern Brazil: an integrated approach using physical and land-use elements   总被引：2，自引：1，他引：1  

Paulo Valladares Soares  Sueli Yoshinaga Pereira  Silvio Jorge C. Simoes  George de Paula Bernardes  Sérgio Augusto Barbosa  Isabel Cristina B. Trannin 《Environmental Earth Sciences》2012,67(6):1685-1694

This work describes the methodological approach used for mapping the potential infiltration areas of the Guaratinguetá watershed (160?km²), situated in Southeastern Brazil. The method is considered a qualitative approach, which takes into account thematic maps (geology, pedology, geomorphology, and land use/land cover) and the precipitation spatial distribution. A group of experts in Earth Sciences and Geotechnical Engineering has applied an infiltration potential scale factor that ranges from 5 (highest influence) to 1 (lowest influence). The final infiltration map was produced using several ArcGIS^? tools. The results showed that the most suitable (very high) infiltration areas represent only around 7% of the watershed area, which are associated with smooth and gentle hills, fluvial Tertiary sediments and yellow oxisols. However, growing impacts caused by land farming and urban developments require urgent planning for this region. Areas with high to moderate capacity of infiltration represent around 56% of the watershed and are found in the domain of igneous-metamorphic rocks associated with steep hill-slopes and relatively well-preserved forest fragments. This region requires a land-use strategy, such as reforestation programs, in order to increase the infiltration capacity of the watershed.  相似文献   

Retrograde alterations of phyllosilicates in low-grade metapelite: a case study from the Szendr? Paleozoic, NE-Hungary     

Péter árkai  Isabel Abad  Fernando Nieto  Tibor Németh  Péter Horváth  Viktória K. Kis  Katalin Judik  Juan Jiménez-Millán 《Swiss Journal of Geoscience》2012,105(2):263-282

Frequently, at temperatures lower than the metamorphic peak conditions, slates undergo mineral transformations, usually mediated by fluids. We have studied core material of an epizonal slate series (Szendr? Mountains, NE-Hungary) to reconstruct the post-metamorphic lower-T hydrothermal alterations using petrographic, X-ray diffraction, electron microprobe methods, and transmission electron microscopy. The borehole crosscuts an upper part of the ca. 600?C800?m Lower-Carboniferous flysch-like Szendr? Phyllite Formation. The samples were metamorphosed reaching epizonal conditions with a mineral assemblage characterized by quartz, muscovite, chlorite and albite. Even in the freshest samples, break-up and loosening of the regional metamorphic structure was observed, with cracks parallel to or crossing the cleavage. In the upper part, chlorite and albite are almost absent, while the presence of paragonite, mixed Na?CK mica, and mixed-layered minerals with smectitic component are characteristic. Goethite, halloysite, and subordinate kaolinite are present in the most altered sample (13.0?m in the profile) which may indicate the position of the fissures in which the circulation of the post-metamorphic fluids was the most intense. Muscovite is the only mica from the lower part of the profile and chlorite becomes a significant constituent, whereas paragonite, halloysite, and kaolinite are missing. Discrete smectite is present in all the samples in spite of being incompatible with the prograde evolution of the sequence. The interleaved smectite layers in chlorite and muscovite/chlorite mixed-layers show at the lattice level textural characteristics indicative of a later alteration process. After the metamorphic peak at epizonal conditions, the introduction of hot fluids through the fractures gave rise to the crystallization of Na?CK white micas and muscovite/chlorite under anchizonal conditions. In a final stage of the hydrothermal process, the cooling of the circulating fluids favored the formation of halloysite and kaolinite in the areas near to the fissures, smectites in the samples far away from the fractures, and locally, goethite. The Fe₂O₃ content increasing upwards indicates oxidizing conditions in the late stage of hydrothermal activity and/or eventually, an influence of a younger near-surface weathering.  相似文献   

A first estimation of tsunami hazard of the Pacific coast of Costa Rica from local and distant seismogenic sources     

Chacon-Barrantes  Silvia  Arozarena-Llopis  Isabel 《Ocean Dynamics》2021,71(8):793-810

Ocean Dynamics - Costa Rica has been affected by several local and distant tsunamis in the past, but the historical information is scarce and incomplete. Its Pacific coast stretches for over a...  相似文献   

Heavy metal concentrations in sediment, benthic invertebrates and fish in three salt marsh areas subjected to different pollution loads in the Tagus Estuary (Portugal)   总被引：3，自引：0，他引：3  

França S  Vinagre C  Caçador I  Cabral HN 《Marine pollution bulletin》2005,50(9):998-1003

  相似文献   

Glacial rapid variability in deep-water temperature and δO from the Western Mediterranean Sea     

Isabel Cacho  Nick Shackleton  Harry Elderfield  Francisco J. Sierro  Joan O. Grimalt 《Quaternary Science Reviews》2006,25(23-24):3294

Deep-water temperatures (DWTs) from the Western Mediterranean Sea are reconstructed for the last 50 ka based on the analysis of Mg/Ca ratios in benthic foraminifera from core MD95-2043 collected in the Alboran Sea. The exceptionally high sedimentation rates of this core and the robust chronology available allow discussion of the results in the context of the Dansgaard–Oeschger (D–O) rapid climatic variability. The applicability of Mg/Ca thermometry in the Western Mediterranean Deep-Water mass (WMDW) is first tested by the analysis of different benthic species in a collection of Mediterranean core tops. The results indicate the need of a readjustment of the existing Cibicidoides spp. calibrations in order to reconstruct present Western Mediterranean DWT values (12.7 °C). Different physiological effects in the Mg uptake between the C. pachydermus living in different regions could account for this offset in the Mediterranean samples. Consequently, the obtained DWT record still has many uncertainties in absolute terms but trends provide valuable information on past changes in WMDW conditions. The DWT record shows significant oscillations in relation to the D–O cycles, colder values occurred during the time of D–O stadials and warmer ones during D–O interstadials. Surprisingly, the coldest DWTs occurred during the time of Heinrich Event 4 (HE4) and not during the Last Glacial Maximum (LGM) when DWTs were mostly warm. These and other particular features of the DWT reconstruction mimic changes in the vegetation from the Eastern Mediterranean indicating the control of the Mediterranean climate on the DWT record. Paired analyses of Mg/Ca and δ¹⁸Occ (calcite δ¹⁸O) provide the opportunity to reconstruct deep-water δ¹⁸O (δ¹⁸Odw) and past salinities and hence changes in past WMDW density. Due to the large error associated with these calculations, they can only be discussed in terms of relative changes between different intervals. The results suggest the dominance of a heavier water end member during glacial times and a lighter one during the early Holocene in relation to the δ¹⁸Odw conditions present today. Densest WMDW were formed during most of Marine Isotopic Stage (MIS) 2 and during the D–O Stadials not associated with HEs, while lightest WMDW dominated during D–O Interstadials. The δ¹⁸Odw record shows a D–O variability pattern likely controlled by changes in the composition and intensity of the local run-off and also to changes in the δ¹⁸Ow signal of the Atlantic inflow. Changes in the residence time of the Mediterranean waters, governed by the global sea level, are also considered to exert an important role governing Mediterranean δ¹⁸Ow and salinity, particularly during MIS 2. Overall, our results are consistent with the formation of dense WMDW during D–O stadials and even denser during most of MIS 2.  相似文献   

A review of Late Pleistocene and Holocene biogeography of highland Mediterranean pines (Pinus type sylvestris) in Portugal, based on wood charcoal     

Isabel Figueiral  Christopher Carcaillet 《Quaternary Science Reviews》2005,24(23-24):2466-2476

The historical biogeography of highland Mediterranean pines is explored based on Late Pleistocene and Holocene charcoal from Portugal (Iberian Peninsula, SW Europe). The earliest presence of Pinus type sylvestris (including P. nigra, P. sylvestris and P. uncinata) is recorded in archaeological layers dated at ca 23,900 BP, during the Full Glacial. The abundance of remains identified as Pinus type sylvestris suggests that this was a frequent taxon, at least at middle altitudes. Significant occurrences were recorded up until ca 11,000 BP, at the end of the Lateglacial warming period. From the early Holocene onwards the presence of Pinus type sylvestris is recorded only sporadically, but at least up to 2000 years ago. The competition with other tree and shrub species favoured by the Holocene warming may have triggered the decline of highland pines in Portugal. Eventual anthropogenic impact is also considered as playing a role in its regional decline, such as increasing fire frequency resulting from amplified land use since the Neolithic.  相似文献   

Biomonitoring with benthic macroalgae and direct assay of heavy metals in seawater of the Oporto coast (northwest Portugal)   总被引：2，自引：0，他引：2  

M.C.Fernanda Leal  M.Teresa Vasconcelos  Isabel Sousa-pinto  João P.S. Cabral 《Marine pollution bulletin》1997,34(12):1006-1015

The concentrations of dissolved Cd, Cu, Hg and Pb in seawater and algae (Enteromorpha spp. and Porphyra spp.) were determined in parallel on three beaches located in the Oporto coast (Portugal), during 8 successive months, comprising periods of low and high biological productivity. The concentrations of dissolved metals in seawater varied markedly during the sampling period and exhibited seasonality. The concentrations of Cd were high in autumn and winter, but low in spring. The concentrations of Cu and Hg were high in autumn, low in winter and peaked in May. The concentrations of Pb were low in autumn and winter, and also peaked in May. It is likely that biological activity was, at least partially, responsible for the observed seasonal changes. The mean concentrations of dissolved metals in seawater were similar to those reported for polluted and industrialized european coastal areas. Metal concentration factors, calculated month-to-month for each alga, metal and site, varied markedly during the sampling period, indicating that concentration factors based on single or few determinations could be misleading. On the contrary, mean concentration factors (calculated by dividing the mean metal concentration in the algae by the mean metal concentration in seawater) were relatively constant at all three sites, indicating that in the Oporto coast, Enteromorpha spp. can be used to estimate the mean concentration of dissolved Cd, Cu and Hg in seawater, and Porphyra spp., the mean concentration of Cd, Cu and Pb. However, considering that future estimates of the concentrations of these metals in seawater should be based on determinations of the metal contents in Enteromorpha spp. and Porphyra spp. carried out on several occasions spanning a considerable period of time, the use of these algae as monitors of heavy metal pollution can have limited practical advantages over the direct assay of the metals in seawater.  相似文献