3-D wave propagation in fluid-filled irregular boreholes in elastic formations

Different seismic testing techniques rely on the propagation of acoustic waves in fluid-filled boreholes from sources placed within the borehole and in the solid media. The interpretation of the signals recorded relies on understanding how waves propagate in the borehole and its immediate vicinity. It is known that very complex wave patterns can arise, depending on the distance between the source and the receiver, and their placement and orientation relative to the axis of a circular borehole. The problem becomes more complex if the cross-section is not circular, conditions for which analytical solutions are not known. In this work, the Boundary Element Method (BEM) is used to evaluate the three-dimensional wave field elicited by monopole sources in the vicinity of a fluid-filled borehole. This model is used to assess the effects of the receiver position on the propagation of both axisymmetric and non-axisymmetric wave modes when different borehole cross-sections are used. Both frequency vs. axial-wave number responses and time-domain responses are calculated.     

A new procedure to estimate the RUSLE EI30 index, based on monthly rainfall data and applied to the Algarve region, Portugal

One of the best indicators of the potential erosion risks is the rainfall–runoff erosivity factor (R) of the revised universal soil loss equation (RUSLE). Frequently, however, there is not enough data available to compute the R value, and other parameters, such as the modified Fournier index (F_mod), are used instead. But RUSLE is less effective if only the alternative procedures exist. One of the major discrepancies between R and the alternative parameters is time resolution: individual storms are used to calculate R while monthly averages over the year are used to calculate F_mod.

In this study, a multiple linear regression (r²=0.89) involving monthly EI₃₀, monthly rainfall for days with ≥10.0 mm and monthly number of days with rainfall ≥10.0 mm, for the Algarve region, is presented. Twenty-seven years of monthly rainfall erosivity values were computed for the 32 standard daily-read raingauge stations of the Algarve region.     

Hydrogeologic Behavior of an Alluvial Aquifer,Salta Province,Argentina: Simulations of Hydraulic Conductivity Field,Groundwater Flow,and Chloride Migration

This work was designed to analyze the hydrogeological behavior of an alluvial aquifer in the River Mojotoro basin site in the Province of Salta, Argentina. The study area presents coarse-grained sediments with high infiltration capacity. The hydraulic conductivity field is affected by the physical heterogeneity of the medium and a geostatistical method, kriging, was used to construct this field from local measurements. The groundwater flow velocity field is computed using a hybrid mixed finite-element method and small variations in the flow directions were determined. Given the existence of a point source of chloride in the region under study, the spatial distribution of the generated plume in the saturated zone is analyzed. The advection-diffusion equation describing the transport of chloride in vertical and horizontal cross-sectional planes of the aquifer is discretized employing a method of characteristics combined with a mixed finite-element procedure, which provides an efficient method to eliminate spurious numerical oscillations and handle the convective term in the equation. The migration of chloride shows patterns, which are affected by the litologic heterogeneities of the aquifer and the regional groundwater flow.     

Temporal variability of throughfall as a function of the canopy development stage: from seasonal to intra-event scale

ABSTRACT

The interception process impacts rainfall magnitude and intensity under the canopy. In this study, the effect of plant interception on throughfall characteristics was assessed in the deciduous Caatinga vegetation, at different canopy development stages and for temporal scales ranging from seasonal to the intra-event scale. Throughfall and stemflow percentages were slightly higher at the onset of the rainy season, when leaf area density is low, with resulting lower interception losses. However, there was no statistical difference among the variables at the seasonal scale. At the intra-event scale, average and maximum throughfall intensity at different time intervals showed statistical difference between the stages of canopy development. Regardless of leaf area density and rainfall depth, vegetation is able to retain all the water up to 2 min in the beginning of each rainfall event with accumulated rainfall smaller than 0.6 mm. Furthermore, the Caatinga vegetation attenuates the rainfall intensity by 30–40%.     

Amazonsaurus maranhensis gen. et sp. nov. (Sauropoda, Diplodocoidea) from the Lower Cretaceous (Aptian–Albian) of Brazil

A new genus and species of an Aptian–Albian sauropod from the Itapecuru Formation, northern Brazil, Amazonsaurus maranhensis, is described. It is known from an incomplete, but diagnostic postcranial skeleton. The new taxon possesses several autapomorphies, such as the anterior caudal vertebrae with lateral laminae formed by the coalescence of the spinoprezygapophyseal and postzygodiapophyseal laminae and, to a lesser extent, of the postzygodiapophyseal laminae. It exhibits many synapomorphies supporting its inclusion in the Diplodocoidea. These include high caudal neural arches and anterior caudal neural arches with spinoprezygapophyseal laminae on the lateral aspect of the neural spine. This record is consistent with previous hypotheses on the existence of a community of Afro-South American dinosaurs.     

Metamorphic path constrained by metapelitic rocks from the inner Aiuruoca-Andrelândia nappe, south of the São Francisco craton, SE Brazil

A Nappe system south to southwest of the São Francisco Craton represents the southern extension of the Brasília belt and describes an inverted metamorphic pile of greenschist facies toward amphibolite facies. The Aiuruoca-Andrelândia nappe is one of the nappes of this system. The hind portion of the Aiuruoca-Andrelândia nappe, south of Caxambu and Aiuruoca (MG), consists of a structural-metamorphic domain transported toward the E-NE. There is a metamorphic transition, from the kyanite zone to kyanite and sillimanite coexistence, until the sillimanite zone. Metapelitic rocks preserve high-pressure parageneses (Rt–Ky–Grt–Ms–Bt–Pl–Qtz) and contain retrograde eclogitic rocks. Sil–Pl–Qtz coronitic intergrowths around garnets are common decompressive textures. Kyanite schists register the P_max of 11 kbar at 660 °C and define a decompressive path until 6–7.5 kbar at 650 °C. These P–T conditions represent the equilibrium in S₂ schistosity (amphibolite facies) and the beginning of the cooling path in the Ky–Sil transition. The decompressive path suggests an extrusional process, immediately after burying at about 60 km. Exhumation controlled by convergent events, related to the São Francisco Plate subduction and tectonic erosion, took these units, isothermally, to higher levels (20–33 km). Later, the metamorphic path shifted toward near-isobaric cooling.     

Uberabasuchus terrificus sp. nov., a New Crocodylomorpha from the Bauru Basin (Upper Cretaceous), Brazil

A new fairly complete and articulated skull of a Peirosauridae crocodylomorph from Bauru Basin (Late Cretaceous), Brazil, is described. The fossil is from a level of clayish sandstone within Serra do Veadinho sequence, Peirópolis, Uberaba County, Minas Gerais State. The sedimentary strata of Serra do Veadinho belong to the Marília Formation (Serra da Galga Member), Bauru Group, considered to be Campanian-Maastrichtian in age. The species -Uberabasuchus terrificus sp. nov. - is a peirosaurid with moderately narrow snout, large round orbits protected by supraorbital bones of triangular shape and an antorbital fenestra bounded posteriorly by a deep groove. This fossil resembles Peirosaurus tormini Price, 1955 in the size pattern of premaxillary teeth and by showing a similar wedge-like maxillary process in the premaxilla. It also shares some morphological features with the other species of the Peirosauridae, namely the crocodylomorph Lomasuchus palpebrosus Gasparini, Chiappe and Fernandez, 1991 from Argentina. Their common features comprise a moderately narrow snout and the deep lateral groove at the premaxilla and maxilla articulation for the reception of a large mandibular tooth. However, the nasal participates in the external nares and does not divide the nasal aperture, producing a “beak-like” structure at the extremity of the snout which is unique among peirosaurids. The stratigraphic setting suggests that the specimen was buried when a flash flood overflowed the shallow channels of a braided fluvial system.

Parsimony analysis of 183 morphological characters is performed for 23 crocodylomorphs. Analysis of the morphological data matrix resulted in three most parsimonious trees (374 steps, CI = 0.679; RI = 0.826). The new species is closely related to Mahajangasuchus and both, in addition to Peirosaurus and Lomasuchus, compose the Peirosauridae.     

Geosteranes: Identification and synthesis of a novel series of 3-substituted steranes

A novel series of 3-alkyl and 3-carboxyalkyl-5β(H)-steranes 7–10 along with a full homologous series of carboxyalkyl-sterane (C₁ to C₆) 4–6 with 3α(H)5α(H) configuration have been identified in marine-evaporitic oils from Fazenda Belém, Potiguar Basin (Brazil) on the basis of mass spectral interpretation. The synthesis of enantiomerically pure 3α-alkyl-5β(H)-cholestane and 3β-alkyl-5α(H)-cholestane standards and their coinjection with petroleum fractions confirmed the structural assignments.