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41.
Tectonic activation,source area stratigraphy and provenance changes in a rift basin: the Early Cretaceous Tucano Basin (NE‐Brazil)
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Felipe T. Figueiredo Renato P. Almeida Bernardo T. Freitas Andre Marconato Simone C. Carrera Bruno B. Turra 《Basin Research》2016,28(4):433-445
Changes in sandstone and conglomerate maturity in tectonically active basins can be considered either as the product of climatic change or of tectonic restructuring of the feeder drainage system. Besides these regional controls, changes in the configuration of local sources can expressively affect basin fill composition. The Early Cretaceous fluvial successions of the Tucano Basin, a rift basin in northeastern Brazil related to the South Atlantic opening, contain one such case of abrupt change in maturity, marked by the passage from pebbly sandstone and conglomerate rich in quartz and quartzite fragments (Neocomian to Barremian São Sebastião Formation) to more feldspathic pebbly sandstone and conglomerate bearing pebbles of varied composition (Aptian Marizal Formation). Systematic analysis of stratigraphic and spatial variation in palaeocurrents and composition of pebbles and cobbles from both units, integrated with the recognition of fluvial and alluvial fan deposits distribution, revealed an abrupt decrease in maturity during the passage from the São Sebastião Formation to the Marizal Formation. This change is explained by exhumation of basement rocks and erosional removal of originally widespread Silurian to Jurassic sandstone and conglomerate units which were a major source of reworked vein quartz and quartzite pebbles to the São Sebastião Formation. Basin border faults activation during the deposition of the Marizal Formation caused adjacent basement uplift above the local erosional base level at the basin borders, whereas during the São Sebastião Formation deposition, the basin border fault scarps probably exposed mineralogically mature sedimentary units. The proposed model has important implications for interpreting changes in sediment maturity in rift basin successions, as similar results are expected where activation of basin border faults occurs after the erosional removal of older sedimentary or volcanic units that controlled syn‐rift successions composition. 相似文献
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43.
Historical contamination of PAHs, PCBs, DDTs, and heavy metals in Mississippi River Delta, Galveston Bay and Tampa Bay sediment cores 总被引:12,自引:0,他引:12
Santschi PH Presley BJ Wade TL Garcia-Romero B Baskaran M 《Marine environmental research》2001,52(1):51-79
Profiles of trace contaminant concentrations in sediment columns can be a natural archive from which pollutant inputs into coastal areas can be reconstructed. Reconstruction of historical inputs of anthropogenic chemicals is important for improving management strategies and evaluating the success of recent pollution controls measures. Here we report a reconstruction of historical contamination into three coastal sites along the US Gulf Coast: Mississippi River Delta, Galveston Bay and Tampa Bay. Within the watersheds of these areas are extensive agricultural lands as well as more than 50% of the chemical and refinery capacity of the USA. Despite this pollution potential, relatively low concentrations of trace metals and trace organic contaminants were found in one core from each of the three sites. Concentrations and fluxes of most trace metals found in surface sediments at these three sites, when normalized to Al, are typical for uncontaminated Gulf Coast sediments. Hydrophobic trace organic contaminants that are anthropogenic (polycyclic aromatic hydrocarbons, DDTs, and polychlorinated biphenyls) are found in sediments from all locations. The presence in surface sediments from the Mississippi River Delta of low level trace contaminants such as DDTs, which were banned in the early 1970's, indicate that they are still washed out from cultivated soils. It appears that the DDTs profile in that sediment core was produced by a combination of erosion processes of riverine and other sedimentary deposits during floods. Most of the pollutant profiles indicate that present-day conditions have improved from the more contaminated conditions in the 1950-1970's, before the advent of the Clean Water Act. 相似文献
44.
Bernardo Vasco Campos Costa Alfredo Candeias Paulo Costa Anbal 《Bulletin of Earthquake Engineering》2022,20(11):6229-6265
Bulletin of Earthquake Engineering - Despite the fact that in recent years Portugal has not seen the occurrence of high-magnitude earthquakes, it remains threatened by these events due to its... 相似文献
45.
Geochemical and petrological constraints on rear-arc magma genesis processes in Ecuador: The Puyo cones and Mera lavas volcanic formations 总被引:1,自引:0,他引:1
Géraldine Hoffer Jean-Philippe Eissen Bernardo Beate Erwan Bourdon Michel Fornari Jo Cotten 《Journal of Volcanology and Geothermal Research》2008
The Puyo scoria cones and the Mera lava flows, two newly recognized volcanic formations dated between Late Pliocene to Middle Pleistocene, extend the limits of the Ecuadorian rear-arc volcanic province some 100 km to the south. The Puyo scoria cones have erupted K-rich absarokites containing olivine, diopside and phlogopite, whereas the Mera lava flows display a basic andesite composition, with olivine and minor augite phenocrysts. In addition to high contents in LILE, LREE and HFSE, the Puyo absarokites exhibit many characteristics of primitive melts, namely high Cr (590–310 ppm) and Ni (330–154 ppm) contents, high Mg# (64–70) and they contain forsteritic olivine (Fo82–89). The composition of the most primary Puyo absarokite was used in petrogenetic models, in order to constrain the genesis of these high-K magmas. Major and trace elements models, as well as isotopic data, indicate that the source of Puyo magmas is a hydrated phlogopite- and garnet-bearing lherzolite. Phlogopite crystallization in the mantle wedge is triggered by the metasomatism by 3–5% of a SiO2-, H2O-rich liquid generated by slab melting. Partial melting of the subducted oceanic crust beneath Ecuador is allowed by the subduction of the young and warm Carnegie Ridge, which modifies the thermal regime of the Benioff zone. A low degree (1–4%) of partial melting of the metasomatized mantle wedge, leaving a variable garnet (4–7%) ± phlogopite (0–4%) lherzolitic residual assemblage, leads to the compositions of the entire Puyo absarokite series and is consistent with previous petrogenetic models developed for the Ecuadorian volcanic arc. Indeed, the homogeneity of isotopic data across the arc suggests a similar source for the whole Ecuadorian magmas. 相似文献
46.
47.
Isabel Caçador Miguel Caetano Bernardo Duarte Carlos Vale 《Marine environmental research》2009,67(2):75-82
Pools of Zn, Cu, Cd and Co in the leaf, stem and root tissues of Sarcocornia fruticosa, Sarcocornia perennis, Halimione portulacoides and Spartina maritima were analysed for a Tagus estuary (Portugal) salt marsh. Pools of Cu and Cd in the salt marsh were higher in spring/summer, indicating a net uptake of these metals during the growing season. Standing stocks of Zn, Cu, Cd and Co in the leaf and stem biomass of S. fruticosa, S. perennis and H. portulacoides showed a strong seasonal variation, with higher values recorded in autumn. The metal-containing leaves and stems that shed in the autumn become metal-containing detritus. The amount of this material washed out from the total marsh area (200 ha) was estimated as 68 kg of Zn, 8.2 kg of Cu, 13 kg of Co and 0.35 kg of Cd. The high tidal amplitude, a branched system of channels and semi-diurnal tidal cycle greatly favour the export of the organic detritus to adjoining marsh areas. 相似文献
48.
Veronica P. Bernardes Aline N. Sousa Camila H. Bernardo Gustavo M. Teixeira Rogério C. Costa Fernando L. Mantelatto Adilson Fransozo 《Marine Ecology》2020,41(5):e12605
This study was motivated by the data about a Rimapenaeus constrictus population from Ubatuba Bay, obtained in the 1990s, and by the establishment of a marine protected area (MPA) in the same region in 2008. We obtained comparable data about the distribution and abundance of this species collected 20 years apart, to evaluate the effectiveness of the MPA, for its preservation and possible changes in the populational profile. Biotic and abiotic data were obtained monthly, in September 1995–August 1996 (period 1 = 1ºP), and in September 2016–August 2017 (period 2 = 2ºP), from five transects within Ubatuba Bay. In total, 710 and 2,362 individuals were caught in the 1oP and 2oP, respectively. Despite this increase in abundance, aspects of the spatial distribution did not change substantially. The high abundance recorded at 5 m of depth was probably due to the creation of the MPA and to the accumulation of detritus at this depth. The high abundance seen in the transect sheltered from waves may be related to sediment heterogeneity, which was higher in this transect, and to the fact that this area is naturally protected from fisheries. In the 1ºP, the highest abundances were recorded in spring and summer, whereas in the 2ºP, they occurred in autumn and winter. This change may be explained by the entrance of the South Atlantic Central Water (SACW), which drives shrimps towards shallower areas. During the 2ºP, a fishing ban occurred in autumn (March 1st until May 31st), which is also when the SACW retreats and water temperature and salinity increase. These two factors combined may have been responsible for the increased shrimp abundance. In conclusion, both conservation practices (MPA and fishing ban) along with the existence of an area naturally protected from fisheries seem to have positively affected the population of R. constrictus, leading to an increase in abundance over the 20-year interval. 相似文献
49.
Discrimination of agricultural crops in a tropical semi-arid region of Brazil based on L-band polarimetric airborne SAR data 总被引:4,自引:0,他引:4
Wagner F. Silva Bernardo F.T. Rudorff Antonio R. Formaggio Waldir R. Paradella Jos C. Mura 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(5):458-463
Recent articles are indicating that polarimetric data provide significantly more information than conventional or multi-polarized images, particularly due to the additional phase information. The objective of this paper is to evaluate the multi-polarized and fully polarimetric L-band airborne SAR-R99B data, in terms of their capability to distinguish among different agricultural crops in the western part of Bahia State, Brazil. Emphasis was given to coffee, cotton and pasture crops which were at well developed growing stages. Discrimination among crops was carried out using graphical analysis of mean backscatter values. Crop classification was performed for single and multiple polarizations, and fully polarimetric images with a classifier that uses the contextual Iterated Conditional Modes–ICM algorithm. The investigation confirmed the potential of L-band multi-polarized and polarimetric airborne SAR-R99B data to distinguish and classify agricultural crops in the tropical condition of the test-site. In addition, it clearly indicated the gradual and considerable improvement that was achieved going from single to three polarizations and from multi-polarized to fully polarimetric images. 相似文献
50.
On the ecohydrology of the Yucatan Peninsula: Evapotranspiration and carbon intake dynamics across an eco‐climatic gradient
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Jorge M. Uuh‐Sonda Hugo A. Gutiérrez‐Jurado Bernardo Figueroa‐Espinoza Luis A. Méndez‐Barroso 《水文研究》2018,32(18):2806-2828
The hydrology and productivity of the ecosystems of the Yucatan Peninsula (YP) are highly constrained by two factors: (a) the lack of surface drainage networks due to the existence of a highly permeable and connected karstic aquifer roughly the size of the peninsula and (b) a climatic gradient that leads to a transition from seasonally dry deciduous and sub‐deciduous tropical forests, in the north‐western and central parts of the Peninsula, to evergreen forests, in the southern and eastern parts. As a result, surface water fluxes of the YP are restricted to evapotranspiration (ET) that are tightly coupled to ecosystems health and gross primary productivity (GPP). The magnitude and seasonal variation of these fluxes are sensitive to climatic variability and perturbations caused by extreme events such as droughts and tropical storms that are frequent in the YP. In this study, we assess the spatio‐temporal dynamics of ET and GPP above average dry and wet conditions through time series analyses of 15 years of remotely sensed data from both Moderate Resolution Imaging Spectroradiometer and Tropical Rainfall Measuring Mission satellite products. Our results show that ET and GPP follow a regional moisture and temperature gradient that highly controls the distribution of ecosystems within the peninsula. We observe that ET and GPP are in phase with the rainy season in the deciduous forests, but for the evergreen forests, only the GPP is in phase. Additionally, and with the exception of droughts on deciduous ecosystems of the northern part of the YP, the productivity of these ecosystems shows a legacy effect, responding more to a defined trajectory (wetting or drying on the previous years), rather than to punctual extreme climatic events. This has implications on the resilience of these ecosystems to natural perturbations of climate. Comparisons between deciduous and evergreen forest indicate that both types of ecosystems have different plant water use strategies in response to hydrologic variability. 相似文献