Deep structure of the northeastern margin of the Parnaiba Basin, Brazil, from magnetotelluric imaging

The magnetotelluric (MT) method has been applied to the determination of the deep resistivity structure of the northeastern margin of the Parnaiba Basin. Transient electromagnetic (TEM) and MT data were collected in early 1999 along a 95 km long N–S line, extending from the coast across the projected subcrop position of a discontinuous fault found to the west of the study area that is believed to be a possible basin‐bounding fault. The MT data were processed to yield the TE‐ and TM‐mode responses and then corrected for static shift using central‐loop and single‐loop TEM data, respectively. Regularized 2D MT inversion was subsequently undertaken using a structured initial model with the near‐surface constrained by TEM inversion results. As a consistency check, we performed another set of 2D inversions using different smooth initial models. The various optimal 2D inversion models show clearly the presence of a major basement trough, over 2 km deep, located about 70 km from the coast. We interpret it as possibly marking the main basin margin and suggest that it may have implications for groundwater resource development in the area.     

Glacial flood pulse effects on benthic fauna in equatorial high‐Andean streams

Equatorial glacier‐fed streams present unique hydraulic patterns when compared to glacier‐fed observed in temperate regions as the main variability in discharge occurs on a daily basis. To assess how benthic fauna respond to these specific hydraulic conditions, we investigated the relationships between flow regime, hydraulic conditions (boundary Reynolds number, Re*), and macroinvertebrate communities (taxon richness and abundance) in a tropical glacier‐fed stream located in the high Ecuadorian Andes (> 4000 m). Both physical and biotic variables were measured under four discharge conditions (base‐flow and glacial flood pulses of various intensities), at 30 random points, in two sites whose hydraulic conditions were representative to those found in other streams of the study catchment. While daily glacial flood pulses significantly increased hydraulic stress in the benthic habitats (appearance of Re* > 2000), low stress areas still persisted even during extreme flood events (Re* < 500). In contrast to previous research in temperate glacier‐fed streams, taxon richness and abundance were not significantly affected by changes in hydraulic conditions induced by daily glacial flood pulses. However, we found that a few rare taxa, in particular rare ones, preferentially occurred in highly stressed hydraulic habitats. Monte‐Carlo simulations of benthic communities under glacial flood reduction scenarios predicted that taxon richness would be significantly reduced by the loss of high hydraulic stress habitats following glacier shrinking. This pioneer study on the relationship between hydraulic conditions and benthic diversity in an equatorial glacial stream evidenced unknown effects of climate change on singular yet endangered aquatic systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Built environment and agricultural value at risk from Hurricane Irma flooding in Florida (USA)

Natural Hazards - Flooding is the most costly type of natural disaster, as well as the most frequent. To provide risk-based flood insurance, providers must be able to accurately determine an...     

Shock deformation confirms the impact origin for the Cerro do Jarau,Rio Grande do Sul,Brazil, structure

Cerro do Jarau is a conspicuous, circular morpho‐structural feature in Rio Grande do Sul State (Brazil), with a central elevated core in the otherwise flat “Pampas” terrain typical for the border regions between Brazil and Uruguay. The structure has a diameter of approximately 13.5 km. It is centered at 30^o12′S and 56^o32′W and was formed on basaltic flows of the Cretaceous Serra Geral Formation, which is part of the Paraná‐Etendeka Large Igneous Province (LIP), and in sandstones of the Botucatu and Guará formations. The structure was first spotted on aerial photographs in the 1960s. Ever since, its origin has been debated, sometimes in terms of an endogenous (igneous) origin, sometimes as the result of an exogenous (meteorite impact) event. In recent years, a number of studies have been conducted in order to investigate its nature and origin. Although the results have indicated a possible impact origin, no conclusive evidence could be produced. The interpretation of an impact origin was mostly based on the morphological characteristics of the structure; geophysical data; as well as the occurrence of different breccia types; extensive deformation/silicification of the rocks within the structure, in particular the sandstones; and also on the widespread occurrence of low‐pressure deformation features, including some planar fractures (PFs). A detailed optical microscopic analysis of samples collected during a number of field campaigns since 2007 resulted in the disclosure of a large number of quartz grains from sandstone and monomict arenite breccia from the central part of the structure with PFs and feather features (FFs), as well as a number of quartz grains exhibiting planar deformation features (PDFs). While most of these latter grains only carry a single set of PDFs, we have observed several with two sets, and one grain with three sets of PDFs. Consequently, we here propose Cerro do Jarau as the seventh confirmed impact structure in Brazil. Cerro do Jarau, together with Vargeão Dome (Santa Catalina state) and Vista Alegre (Paraná State), is one of very few impact structures on Earth formed in basaltic rocks.     

The Effect of Sunspot Weighting

Although W. Brunner began to weight sunspot counts (from 1926), using a method whereby larger spots were counted more than once, he compensated for the weighting by not counting enough smaller spots in order to maintain the same reduction factor (0.6) as was used by his predecessor A. Wolfer to reduce the count to R. Wolf’s original scale, so that the weighting did not have any effect on the scale of the sunspot number. In 1947, M. Waldmeier formalized the weighting (on a scale from 1 to 5) of the sunspot count made at Zurich and its auxiliary station Locarno. This explicit counting method, when followed, inflates the relative sunspot number over that which corresponds to the scale set by Wolfer (and matched by Brunner). Recounting some 60,000 sunspots on drawings from the reference station Locarno shows that the number of sunspots reported was “over counted” by \({\approx}\,44~\%\) on average, leading to an inflation (measured by an effective weight factor) in excess of 1.2 for high solar activity. In a double-blind parallel counting by the Locarno observer M. Cagnotti, we determined that Svalgaard’s count closely matches that of Cagnotti, allowing us to determine from direct observation the daily weight factor for spots since 2003 (and sporadically before). The effective total inflation turns out to have two sources: a major one (15?–?18 %) caused by weighting of spots, and a minor source (4?–?5 %) caused by the introduction of the Zürich classification of sunspot groups which increases the group count by 7?–?8 % and the relative sunspot number by about half that. We find that a simple empirical equation (depending on the activity level) fits the observed factors well, and use that fit to estimate the weighting inflation factor for each month back to the introduction of effective inflation in 1947 and thus to be able to correct for the over-counts and to reduce sunspot counting to the Wolfer method in use from 1894 onwards.     

Effects of parasitism and environment on shell size of the South American intertidal mud snail Heleobia australis (Gastropoda)

The aim of this work was to evaluate the effects of parasitism and certain environmental factors on the shell size of Heleobia australis (Hydrobiidae, Cochliopinae). We report sporocysts and metacercariae of Microphallus simillimus (Microphallidae, Trematoda) parasitizing the gonad and digestive gland of H. australis specimens from two sites of Bahía Blanca estuary, Argentina. The prevalence of infection was significantly higher (34.17% in winter and 68.14% in late spring) in snails from the outer estuary at Site 2 than in those from the inner estuary at Site 1 (5.88% and 4.71% respectively). The only known definitive host for this digenean is the white-backed stilt Himantopus melanurus (Recurvirostridae, Aves), most abundant in the estuary during winter. Parasitism by M. simillimus causes variations in the shell dimensions of H. australis, the shells of infected snails being narrower than those of uninfected snails. Snails from Site 2 were found in general to be significantly smaller than those at Site 1, possibly as a result of differences in environmental factors such as the degree of exposure to wave energy, the allocation of energy to reproduction rather than growth (induced by predation and/or parasitic castrators) and anthropogenic stressors.     

Modelling hydrostratigraphy and groundwater flow of a fractured and karst aquifer in a Mediterranean basin (Salento peninsula, southeastern Italy)

The control exerted by the hydrostratigraphic structure on aquifer recharge, groundwater flow and discharge along the coastal areas of a Mediterranean basin (Salento peninsula, about 5,000?km² wide, southern Italy) is assessed through the development and application of a groundwater flow model based on the reconstruction of the hydrostratigraphic architecture at the regional scale. The hydrostratigraphic model, obtained by processing surface and subsurface data, is applied to map the top of the main aquifer, which is hosted in the deep hydrostratigraphic unit corresponding to Cretaceous and Oligocene limestones with complex geometrical relationships with the sea. It is also used to estimate the aquifer recharge, which occurs by percolation through overlying younger sediments with low permeability. These data are completed with information about the soil use to estimate water abstraction for irrigation and with literature data to estimate the water abstraction for drinking and industrial purposes. The above-sketched conceptual model is the basis for a finite difference groundwater 2D pseudo-stationary flow model, which assumes the following fundamental approximations: the fractured and karst limestone hydrostratigraphic unit can be approximated, at the model scale, as a continuous medium for which the discrete Darcy??s law is valid; the transition zone between salt and fresh water is so small with respect to the grid spacing that the Ghyben?CHerzberg??s approximation for a sharp interface can be applied. Along the coastline different boundary conditions are assigned if the top of the limestone hydrostratigraphic unit lies either above the sea level (the aquifer has a free surface and fresh water is drained), or below the sea level (the aquifer is under pressure and the contact with sea occurs off-shore). The groundwater flow model correctly predicts the areas where the aquifer is fully saturated with salt water.     

Mississippian coral assemblages from the Khenifra area,Central Morocco: Biostratigraphy,biofacies, palaeoecology and palaeobiogeography

Analysis of Mississippian coral assemblages from the Khenifra region of Central Morocco together with data from foraminiferal/algal microfossils has established new age dating of 5 localities within the Azrou–Khenifra Basin: Souk El Had and Sidi Lamine, where corals occur mainly in biostromes protected by oolitic shoals, Tabainout, where corals have been recorded in different environments related to microbial mounds, Alhajra Almatkouba, where corals occur in biostromal reworked beds and Tiouinine, where corals occur in a well structured, fringing reef. This study demonstrates the presence of richer more diverse coral assemblages than previously recorded, in a variety of environmental settings. These coral assemblages strengthen correlations with the Adarouch area in the NE part of the Azrou–Khenifra Basin. It is emphasised that in the upper Viséan there are close similarities with rugose coral assemblages in other parts of the Western Palaeotethys including North Africa, SW Spain and NW Europe, and that all belong to the same biogeographic province.