Geofísica
Resumo | The late Ediacaran record encompasses frequent occurrences of 34S-enriched pyrites, which can surpass the coexisting sulfate isotope values. Deciphering what controls this marine isotope record is important to understand its biogeochemical implications, especially considering the early metazoan evolution. We present here multiple sulfur isotope compositions from pyrites of two distinct geotectonic settings within the late Ediacaran-early Cambrian West Gondwana, allowing to constraint spatial and temporal distribution of 34S-enrichments. |
Resumo | This study introduces a DC 2D inversion algorithm that employs conjugate gradients relaxation to solve the maximum likelihood inverse equations. The adoption of the maximum likelihood algorithm was motivated by its advantage of not requiring the calculation of electrical field derivatives. While the inversion algorithm based on the maximum likelihood inverse theory has been extensively described for 3D DC inversion using finite differences modelling, its application in the 2D finite element method has received limited attention. |
Resumo | Magnetotactic bacteria produce chains of nanoscopic iron minerals used for navigation, which can be preserved over geological timescales in the form of magnetofossils. Micrometer-sized magnetite crystals with unusual shapes suggesting a biologically controlled mineralization have been found in the geological record and termed giant magnetofossils. The biological origin and function of giant magnetofossils remains unclear, due to the lack of modern analogues to giant magnetofossils. |
Resumo | Unveiling the tempo and mode of animal evolution is necessary to understand the links between environmental changes and biological innovation. Although the earliest unambiguous metazoan fossils date to the late Ediacaran period, molecular clock estimates agree that the last common ancestor (LCA) of all extant animals emerged ~850 Ma, in the Tonian period, before the oldest evidence for widespread ocean oxygenation at ~635–560 Ma in the Ediacaran period. Metazoans are aerobic organisms, that is, they are dependent on oxygen to survive. |
Resumo | Investigating soil and water contamination is essential for assessing environmental risks and monitoring remediation processes. This study, located in São Paulo, Brazil, highlights the presence of chlorinated solvents, especially tetrachloroethylene, with the application of remediation measures such as chemical oxidation. Both contamination and remediation processes have led to changes in geophysical signatures, enabling the use of electrical resistivity, despite challenges in urban areas due to consolidated infrastructure. |
Resumo | Fluvial erosion of the Earth's crust creates valleys ranging from hundreds of meters to a few kilometers wide. The resulting unloading is supported by the flexural rigidity of the continental lithosphere. As a result, the bending of the lithosphere around individual river valleys is usually imperceptible in the landscape, specially in tectonically quiescent environments. |
Resumo | The 4.5 mb Amargosa earthquake was the largest event to occur in the state of Bahia, NE Brazil, in more than 100 years. It caused intensity VI MM in the epicentral area and was felt up to more than 200 km away. A previously published focal mechanism determination had suggested a normal faulting event at about 10 km depth. However, our detailed analyses of regional and teleseismic records show, in fact, a reverse faulting mechanism and a very shallow depth of about 1 km. |
Resumo | Seismometer component orientation is one of the most critical parameters for seismology, especially for methods that take wave field polarization effects into account, such as receiver functions, seismic anisotropy, surface wave dispersion and seismic tomography. Using P-wave particle motion combined with directional statistics, we estimated the orientation for 90 stations of the Brazilian Seismographic Network (RSBR), corresponding to 105 seismometers. The difference between the number of stations (90) and seismometers (105) is due to instrument replacement during station operation. |
Resumo | The appearance of the early biomineralized skeletons during the latest Ediacaran was one of the most important evolutionary gains for the ancient animals' lineage. This evolutionary innovation likely represents a pivotal shift in ecology and the interactions between the geosphere and biosphere. Among these fossils, Cloudina stands out as the oldest macroscopic biomineralized metazoan that achieved widespread distribution. |
Resumo | O período formativo (cerca de 4.000 a 2.000 AP) no continente americano foi caracterizado por ocupações humanas ao longo da costa, rios, lagos, e nos interflúvios das terras altas. No Brasil, existe agora uma tendência de negar a existência do Formativo devido a um suposto vazio popular amazônico neste período. Os estudos nas estearias da Baixada Maranhense, juntamente com investigações anteriores em outras partes do Brasil, sugerem que o Formativo certamente existiu e mostram que estes sítios possivelmente foram a última fronteira do Formativo na Amazônia em sua porção oriental. |
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