Ginaldo Ademar da Cruz Campanha

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

The evolutionary events during the Ediacaran–Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record. We report an assemblage of ichnofossils from Ediacaran–Cambrian siltstones in Brazil, alongside U–Pb radioisotopic dates that constrain the age of the oldest specimens to 555–542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μm in diameter, indicative of small-bodied, meiofaunal tracemakers. Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal–sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran.Trace fossils from the Ediacaran–Cambrian transition of Brazil are interpreted as the remains of burrows made by a nematoid-like organism moving through sediment: these organisms are interpreted as the oldest known fossil meiofaunal bilaterians.

A faixa de dobramento Paraguai na Serra da Bodoquena e depressão do Rio Miranda, Mato Grosso do Sul

The Southern Paraguay Belt is a typical fold-and-thrust belt. Its geological evolution began with a continental rifting process, probably at the end of the Cryogenian, evolving into a restricted sea and an extensive marine transgression at the end of the Ediacaran. The final collisional event occurred during the Lower Cambrian, with post-collisional magmatism during the Upper Cambrian. The Corumba Group is divided into five formations (Cadiueus, Cerradinho, Bocaina, Tamengo and Guaicurus). The Puga Formation is correlated to the Cerradinho and Cadiueus formations. This stratigraphy can be seen even in the most deformed parts located in central-eastern area. In the far west of the area, the Corumba Group is deposited above an unconformity in the Rio Apa cratonic block. The name Agachi Schists is suggested for the schists located at the easternmost portion of the area. During the Ediacaran period, whereas, in the east part of the area, the Cuiaba Group was affected by deformation, metamorphism and arc-related granites, in the west part of the area, the Tamengo and Guaicurus formations were deposited, probably in a context of foreland basin. Up to three superimposed coaxial folding events are observed associated with greenschist metamorphism and thrust faults, showing a westward tectonic vergence. WSW - ESE convergence vectors indicate that the collision with the Rio Apa block was slightly oblique. Changes in metamorphism and structural style can be explained by the westward migration of the deformational front. The main thrust faults coincide with important basin boundaries, suggesting that the listric faults of the rift stage were reactived by them.

The inventory of geological heritage of the state of São Paulo, Brazil: Methodological basis, results and perspectives

An inventory of geological sites based on solid and clear criteria is a first step for any geoconservation strategy. This paper describes the method used in the geoheritage inventory of the State of São Paulo, Brazil, and presents its main results. This inventory developed by the geoscientific community aimed to identify geosites with scientific value in the whole state, using a systematic approach. All 142 geosites representative of 11 geological frameworks were characterised and quantitatively evaluated according to their scientific value and risk of degradation, in order to establish priorities for their future management. An online database of the inventory is under construction, which will be available to be easily consulted and updated by the geoscientific community. All data were made available to the State Geological Institute as the backbone for the implementation of a future state geoconservation strategy.

Geoquímica e petrogênese de metabasitos do grupo Votuverava (Terreno Apiaí, Cinturão Ribeira Meridional): evidências de uma bacia retroarco calimiana

O Grupo Votuverava (ca. 1500 - 1400 Ma) faz parte do Terreno Apiai, um segmento do Cinturao Ribeira Meridional. E constituido por turbiditos distais com expressivo magmatismo basico representado por lentes concordantes de metabasito. Vinte amostras de metabasito foram investigadas por meio de analises geoquimicas (elementos maiores e tracos). Tres grupos (G1, G2, G3) foram distinguidos com base em assinaturas Ti/V, padroes de elementos terras raras e perfis multielementos normalizados pelos valores de basaltos de dorsais meso-oceânicas (MORB). Todas as amostras apresentam assinaturas toleiticas. O G1 mostra assinatura de arco vulcânico, com razao Ti/V de 15 - 20, enriquecimento em ions litofilos de grande raio ionico (LILE) e empobrecimento em elementos de alta forca de campo (HFSE) relativos ao MORB. O padrao dos elementos tracos indica importante contribuicao do componente de subduccao. O G2 apresenta composicao geral semelhante ao MORB, com Ti/V de 22 - 28. Contudo, o comportamento dos elementos tracos sugere uma pequena contribuicao do componente de subduccao. O G3 apresenta assinatura de basaltos do tipo MORB enriquecido, com razao Ti/V ao redor de 40 e enriquecimento em LILE e HFSE. A variabilidade entre as razoes TiO2/Yb e Nb/Yb sugere que as rochas G1 e G2 foram geradas por fusao rasa (fontes mantelicas tipo MORB normal e enriquecido, respectivamente). As rochas G3 sao enriquecidas em Ti e Nb, sugerindo interacao entre fontes do tipo MORB e pluma. A coexistencia de metabasitos com composicoes de basaltos toleiticos de arcos vulcânicos e basaltos de dorsais meso-oceânicas, os padroes geoquimicos de forma geral e o ambiente de sedimentacao do Grupo Votuverava sao consistentes com um ambiente de bacia retroarco.

Algorithms for extraction of structural attitudes from 3D outcrop models

The acquisition of geological attitudes on rock cuts using traditional field compass survey can be a time consuming, dangerous, or even impossible task depending on the conditions and location of outcrops. The importance of this type of data in rock-mass classifications and structural geology has led to the development of new techniques, in which the application of photogrammetric 3D digital models has had an increasing use. In this paper we present two algorithms for extraction of attitudes of geological discontinuities from virtual outcrop models: ply2atti and scanline, implemented with the Python programming language. The ply2atti algorithm allows for the virtual sampling of planar discontinuities appearing on the 3D model as individual exposed surfaces, while the scanline algorithm allows the sampling of discontinuities (surfaces and traces) along a virtual scanline. Application to digital models of a simplified test setup and a rock cut demonstrated a good correlation between the surveys undertaken using traditional field compass reading and virtual sampling on 3D digital models. HighlightsWe present two algorithms for attitude calculation from photogrammetric 3D models.We test the algorithms on a simplified setup and a rock cut.The sampling methods demonstrate a good correlation with traditional measures.Virtual sampling must be carried out carefully to avoid errors.

A discordância angular e erosiva entre os grupos Chapada Diamantina e Bambuí (Una) na folha Mirangaba-Bahia

The stratigraphic relationships between the Chapada Diamantina and Bambui (or Una) groups were practically established with the papers of J. C. Branner, a century before. Sometimes that proposed lithostratigraphy was questioned, but we do know now that these arguments were based up incomplete or inadvertent field observations. At the sheet of Mirangaba, central-northern part of Bahia, both the angular and erosional unconformity between the above-mentioned groups are exposed of a conspicuous way, according to their three dimensions, what deserves the special mention here consigned. The quartzites and conglomerates of the Chapada Diamantina group are cropping out as folded and re-fold rock units (general strike ENE-WSW) and they present features of intense superposed erosional processes. Two paleosurfaces were formed and are being exhibited, with complementary features of erosional scarpments, as well as amphitheatres, suppression of some lithostratigraphic units, testimonies-hills (quartzitic islands), etc. The lower pediplan then formed (today with summits >; 500 m) was completely covered by the limestones (Salitre Fm.), where calcilutites are predominating, presenting many algalic edifications. We are not able to affirm that the proterozoic limestone progradation have covered the higher pediplan (today with summits ca. 1,000 m), but there are some testimonies-hills of limestone presenting tops up to 600 m, clearly above the present and predominating surface (Neogene, Velhas Surface), so reiterating that an intense erosional dissecation has occurred (Cenozoic in age) of the limestones. These limestones present monotonous subhorizontal structural attitudes, with the presence of some open folding (ondulations) when they are near of the contacts with the subjacent quartzites. Quite often these limestones were submitted to local ruptural displacements. The polyphasic deformation of the subjacent Chapada Diamantina group is being hypothetically attributed to the Brazilian cycle (as foreland domain of the Riacho do Pontal fold system), but this proposed condition needs to be better constrained, as well as the northern limit of the Sao Francisco Craton (to the north) demands to be reviewed. The basal diamictites of the Bambui Group (Bebedouro Fm.) is only locally cropping out, at the southern and at the northwestern part of the area. The time interval between the deformation of the quartzites and the beginning of the limestones deposition was necessarily very long, some millions of years, and this is an obligatory target for future researches.

Microstructures and K-Ar illite fine-fraction ages of the cataclastic rocks associated to the Camburu Shear Zone, Ribeira Belt, Southeastern Brazil

The Camburu Shear Zone (CSZ) is recognized as a NE-SW trending dextral transcurrent fault and is related to the evolution of the Ribeira Belt, southeastern Brazil. The CSZ ductile regime dates from the Precambrian to the Cambro-Ordovician and it is characterized by a meter to hundreds of meters wide belt of quarzto-feldspathic mylonitic rocks organized in a positive-flower structure. Previous studies postulated that the fault underwent normal reactivation, probably during the Cenozoic, developing metric to centimetric thick intercalations of cemented cataclastic rocks. We concluded that these cataclastic rocks maintained their primary cohesion and were syntectonically silicified by feldspar-to-mica reactions. Cataclasis was shown by the fractal distribution of grains and fragments, dilatancy, rigid body rotation, cataclastic flow, microcracking and microfaulting. Two cataclastic events are described: (i) during the Lower Devonian (402 ± 6 Ma) in a ductile-to-brittle regime with temperatures up to 400°C and development of foliated protocataclasites, and (ii) during the Upper Carboniferous (310.9 ± 8 Ma) in a brittle regime with temperatures up to ~300°C and development of protocataclasites and crushed breccias. It is then suggested that the CSZ cataclasites were formed during two Paleozoic reactivation events associated to a far-field orogenic effect induced by the Precordillera and Chanica orogenic cycles in the western margin of the Gondwana Paleocontinent.