Enterotoxemia, a disease that affects domestic ruminants, is caused mainly by the epsilon toxin from Clostridium perfringens type D. Its eradication is virtually impossible, control and prophylaxis are based on systematic vaccination of herds with epsilon toxoids that are efficient in inducing protective antibody production. The use of recombinant toxins is one of the most promising of these strategies. This work evaluates the potency of a Cl. perfringens type D epsilon toxoid expressed by Escherichia coli administered to goats, sheep, and cattle. The etx gene was cloned into the pET-11a plasmid of E. coli strain BL21 to produce the recombinant toxin. Rabbits (n=8), goats, sheep, and cattle (n=5 for each species) were immunized with 0.2mg of the insoluble recombinant protein fraction to evaluate vaccine potency of the epsilon toxoid studied. Antibody titers were 40, 14.3, 26, and 13.1 IU/mL in the rabbit, goat, sheep, and cattle serum pools, respectively. The epsilon toxoid produced and tested in this work is adequate for immunization of ruminants against enterotoxemia.

Regional patterns of crustal stresses in Brazil were studied with a detailed breakout analysis performed in 541 wells distributed throughout the country: 48 1 from basins along the continental margin, and 60 from intracratonic basins. A total of about 591 km of cumulative well length, digitally sampled at 0.15 m intervals, was analysed. Most intervals (80 per cent) are confined between -400 and -4000 m. Only wells that deviate less than 10" from the vertical were considered. For a given well (1) the mean orientation and the standard deviation of each interval with breakouts were calculated, (2) all intervals with mean breakout orientations less than 10" from the orientation of the hole deviation were discarded, ( 3 ) all intervals with standard deviations less than 12" were selected, (4) the selected breakouts were weighted by their interval length to calculate the mean orientation and standard deviation of the whole well, and (5) the final results were classified according to the World Stress Map criteria. Thus, 16 wells were classified as A (a total of 7.2 km of breakouts), 42 as B (7.1 km), 78 as C (7.4 km), 205 as D (3.3 km), 184 as E (0.7 km) and 16 were discarded.In most basins, the breakout orientations from different wells were usually consistent for qualities A, B and C, allowing a good estimate of the regional maximum horizontal stress (SHmax); wells classified as quality D showed a large scatter. The regional SHmax determined from breakouts is generally in good agreement with the available nearby focal mechanisms. The main trends of SHmax are (1) NW-SE, parallel to the coast, along the equatorial marginal basins, (2) E-W in the Alagoas Basin, (3) NNE-SSW, parallel to the coast, in the Sergipe and Reconcavo basins, and (4) NW-SE in the Middle Amazon Basin.In the equatorial and eastern continental margins, north of 15"S, breakouts and focal mechanism measurements indicate that the SHmax orientation is remarkably parallel to the coastline, following a 90" bend of the coast in northeastern Brazil. Because the theoretically predicted intraplate stresses in northern Brazil trend about WNW to ENE (e.g. Meijer 1995;Coblentz & Richardson 1996), we interpret our observations as indicating that local sources of stress at the continental margins (e.g. flexural stresses and lateral density contrasts) dominate the plate-wide stresses and may have been underestimated in theoretical stress models of the South American plate.The new stress data (136 A-C quality out of a population of 541 wells) cover a region of mid-plate South America where only 23 data points had been compiled previously in the World Stress Map database. The more detailed observed patterns of the intraplate stress field should be helpful in better constraining future models of the forces driving the South American plate.

The Andean Orogeny in South America has lasted over 100 Ma. It comprises the Peruvian, Incaic and Quechuan phases. The Nazca and South American plates have been converging at varying rates since the Palaeocene. The active tectonics of South America are relatively clear, from seismological and Global Positioning System (GPS) data. Horizontal shortening is responsible for a thick crust and high topography in the Andes, as well as in SE Brazil and Patagonia. We have integrated available data and have compiled four fault maps at the scale of South America, for the mid-Cretaceous, Late Cretaceous, Palaeogene and Neogene periods. Andean compression has been widespread since the Aptian. The continental margins have registered more deformation than the interior. For the Peruvian phase, not enough information is available to establish a tectonic context. During the Incaic phase, strike-slip faulting was common. During the Quechuan phase, crustal thickening has been the dominant mode of deformation. To investigate the mechanics of deformation, we have carried out 10 properly scaled experiments on physical models of the lithosphere, containing various plates. The dominant response to plate motion was subduction of oceanic lithosphere beneath continental South America. However, the model continent also deformed internally, especially at the margins and initial weaknesses.

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[1] We analyzed borehole breakout data and drilling-induced tensile fractures derived from resistivity image logs run at 10 oil wells to derive the orientation of the maximum horizontal stress S Hmax from the Potiguar Basin in the continental margin of Brazil. Stress magnitudes are derived from density logs for the vertical stress, mini-frac tests for the minimum horizontal stress S hmin , and rock strength laboratory analysis to estimate the S Hmax magnitudes. We compared these results with the stress regime and S Hmax orientation derived from nine earthquake series located in the crystalline basement, where seismicity is concentrated, and previous breakout data from the basin. In the basin, the S Hmax gradient is 20.0 MPa/km, and the S Hmax /S hmin ratio is 1.154, indicating a normal tectonic stress regime from 0.5 to 2.0 km, whereas the S Hmax gradient of 24.5 MPa/km and S Hmax /S hmin ratio of 1.396 indicate a transition from a normal to strike-slip stress regime at 2.5 to 4.0 km. The deeper stress regime in the basin is similar to that in the basement at 1-12 km depth. This transition of the tectonic stress regime is consistent with an incipient tectonic inversion in the basin. We note that the S Hmax orientation rotates from NW-SE in the western part of the Potiguar Basin to E-W in its central and eastern parts, roughly following the shoreline geometry, indicating that local features such as flexural stresses influence the local (scale < 100 km) stress pattern. We also conclude that the basement is critically stressed, but not the basin.

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This study describes a peculiar, yet common type of fracture showing a staircase trajectory, which forms in rocks with moderately weak planar anisotropies. The staircase fracture trajectory is given by alter nat ing fracture segments oriented parallel to (LaP) or at an angle (ramp) with respect to the lamination/layering. The analyses has been accomplished on travertines, which are continental microbial/hydrothermal deposits having a typical poorly stratifi ed yet strongly laminated texture. In these rocks, porosity and permeability have a high across-lamination variability and are mostly controlled by an interconnected and locally corroded array of permeable layers, fractures, and faults. Structural analysis integrated with analytical modeling provided a conceptual model of staircase fracture localization as a function of the travertine lamination dip. Lamination-parallel fracture segments localize within the porous laminae, mostly at the interface with tight laminae. Ramp-type fracture segments cut the lamination, connecting lamination parallel segments. Two types of staircase fracture can be modeled. The fi rst group develops in sub horizontal to gently dipping deposits (lamination dip < 30°) corresponding to lowenergy depositional environments. The second group relates to staircase fractures developed in moderately to steeply dipping laminations (lamination dip >30°) and corresponds to high-energy environments. Major discoveries of hydrocarbon have been recently made in continental (lacustrine) microbial carbonates in the Brazilian South Atlantic margin, some of which exhibit a texture similar to those usually observed in travertines. Understanding of the lacustrine carbonates is still at an early stage. Given that in modern rift settings, vent-related thermal (travertine) and nonthermal (tufa) carbonates are a major component, the proposed conceptual model of staircase fracture localization contributes to the preparation of a model for the potential occurrence of high-permeability pathways in hydrocarbon and geothermal microbial reservoirs.