Flexural deformation controls on Late Quaternary sediment dispersal in the Garo-Rajmahal Gap,NW Bengal Basin

Subsurface deformation is a driver for river path selection when deformation rates become comparable to the autogenic mobility rate of rivers. Here we combine geomorphology, soil and sediment facies analyses, and geophysical data of the Late Quaternary sediments of the central Garo-Rajmahal Gap in Northwest Bengal to link subsurface deformation with surface processes. We show variable sedimentation characteristics, from slow rates (<0.8 mm/year) in the Tista megafan at the foot of the Himalaya to nondeposition at the exposed surface of the Barind Tract to the south, enabling the development of mature soils. Combined subsidence in the Tista fan and uplift of the Barind Tract are consistent with a N-S flexural response of the Indian plate to loading of the Himalaya Mountains given a low value of elastic thickness (15–25 km). Provenance analysis based on bulk strontium concentration suggests a dispersal of sediment consistent with this flexural deformation—in particular the abandonment of the Barind Tract by a Pleistocene Brahmaputra River and the current extents of the Tista megafan lobes. Overall, these results highlight the control by deeply rooted deformation patterns on the routing of sediment by large rivers in foreland settings.     

Using Clustered Heat Maps in Mineral Exploration to Visualize Volcanic-Hosted Massive Sulfide Alteration and Mineralization

Natural Resources Research - This study proposes an extension of a visualization approach common in biochemistry (the clustered heat maps—CHMs) to geochemical data with the main objective of...     

The influence of light availability and predatory behavior of the decapod crustacean Nephrops norvegicus on the activity rhythms of continental margin prey decapods

The day–night cycle is one of the strongest geophysical cycles modulating species' behavioral rhythms. However, in deep-water continental margins, where light intensity decreases over depth, interspecific competition may alter behavioral responses to day–night cycles. The burrowing decapod crustacean Nephrops norvegicus is a large-size predator in benthic communities, exerting despotic territorial behavior. In this study, we analysed how the effect of light intensity cycles on decapod behavioral rhythms is reduced as one moves from shelves to slopes. In the Western Mediterranean, the predatory behavior and interspecific competition for substrate use of Nephrops increases moving from the shelf (100–110 m) to the slope (400–430 m). Vector fitting and generalized additive models were used to assess the effect of light intensity and behavioral rhythms of N. norvegicus on the temporal variation of prey decapods co-occurring in trawl tow catches carried out on the shelf and the slope during October 1999 and June 2000. The combination of diel variations in light intensity and N. norvegicus abundance influences the activity rhythms of prey decapods in a depth- and seasonal-dependent manner. Light modulation is stronger on the shelf and weaker on the slope, where Nephrops population size is greater. Although present regression analysis does not necessarily imply a direct cause–effect relationship between rhythms of predators and prey, we suggest that Nephrops alters the temporal patterning in the behavior of its prey on the slope, where light intensity is reduced. This alteration is stronger in endobenthic species than in benthopelagic species; the former rely on bottom substrate for the expression of behavioral rhythms, experiencing stronger interspecific competitions with Nephrops at time of activity.     

Trace element distributions in surficial sediments of the northern Tyrrhenian Sea: Contribution to heavy-metal pollution assessment

The trace element distributions in surficial sediment of Tyrrhenian Sea have been investigated as a part of a series of studies on the environmental quality of the area off the Tuscany coast (west-central Italy). This research has focused on the presence of possible contaminated zones; it also provides data for the identification and future monitoring and control of pollution sources. The study of numerous surface sediments and core samples has made it possible to distinguish between heavy-metal enrichments related to natural sources and other anomalies caused by anthropogenic contamination. Over much of the basin, the surface Pb, Cu, Zn, and As contents appear considerably enriched relative to those below 15 cm; among these metals, Pb shows the highest and most widespread enrichment. Only in the case of some coarse-grained sediments close to the mouth of Cecina River it is possible to relate anomalously high Zn contents to natural sources. In all other sampling stations, the enrichments of Pb, Cu, Zn, and As are ascribed to man's influence. The sediment distributions of Co, Cr, and Ni do not seem to be related to anthropogenic activities; rather they mirror influx of materials derived from sources of ophiolitic rock. The distribution of barium shows only two significant positive anomalies, and both are related to natural causes. Concentrations of vanadium are high in a zone close to an important smelting plant; these are thought to be of anthropogenic origin.     

Crust and Upper Mantle Structure in the Caribbean Region by Group Velocity Tomography and Regionalization

An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth.     

Phytoplankton Interannual Variability at Cassino Beach, Southern Brazil (1992–2007), with Emphasis on the Surf Zone Diatom Asterionellopsis glacialis

A long-term study (monthly sampling, 1992 to 2007) was conducted in the surf zone of Cassino Beach, Southern Brazil, in order to detect possible natural and/or anthropogenic disturbances. Surface water temperature (6–29°C) was the only parameter with predictable seasonal variation; salinity (14–38) was inversely related to rainfall (3.1–485.2 mm month⁻¹) and low values followed extreme precipitation periods in 1997/1998 and 2002/2003 (El Ni?o years). Asterionellopsis glacialis and chlorophyll a presented high concentrations and peak frequency until 1998, when an intense mud deposition occurred with concomitant extreme rainfall. It affected the surf zone and beach, changing the hydrology and dissolved inorganic nutrient availability. Six phytoplankton species groups were recognized with distinct responses to this mud deposition. We conclude that large-scale climatic changes, like El Ni?o Southern Oscillation, in conjunction with human activities significantly altered the phytoplankton ecology of the highly dynamic Cassino Beach surf zone.     

Generative Adversarial Network Applied to Ore Type Modeling in Complex Geological Environments

Mathematical Geosciences - In complex geological environments, the spatial domain characterization of different ore types has been one of the most important challenges in the assessment of mineral...