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Early Cretaceous bivalves of the Romualdo Formation, Araripe Basin, northeastern Brazil.
(2024) Guerrini, Vitor Bonatto; Matos, Suzana Aparecida; Fürsich, Franz Theodor; Rodrigues, Mariza Gomes; Varejão, Filipe Giovanini; Warren, Lucas Veríssimo; Assine, Mario Luis; Simões, Marcello Guimarães
The fossil-rich Romualdo Formation (late Aptian/early Albian), Araripe Basin, northeastern Brazil, contains world-renowned Fossillagerstatten characterized by exceptionally preserved fossils. Macro- € invertebrates in this formation are primarily represented by mollusks, echinoids, and decapod crustaceans. Mollusk shells are abundant in certain stratigraphic intervals, forming coquinas or shell pavements. Despite recent advances in our understanding of the taxonomy of certain groups, compre-hensive taxonomic studies are lacking for almost the entire bivalve fauna. Therefore, a detailed taxonomic analysis is presented here. The described bivalves include four new genera (Araripenomia, Ciceromya, Inversatella, Australoeocallista), and six new species (Araripenomia infirma, Inversatella cearensis, Ciceromya edentulosa, Australoeocallista juazeiroi, Legumen kaririense, and Corbulomima delicata), in addition to Musculus maroimensis, Crassatella maroimensis, “Myrtea” sp. and “Tellina” sp. This bivalve fauna mainly consists of cosmopolitan and endemic brackish/marine genera, with Tethyan affinities. The fauna is not homogeneously distributed in the sedimentary succession of the Romualdo Formation, but is constrained to the third order highstand systems tract. Bivalves recorded from muddy facies are strongly dominated by infaunal and semi-infaunal suspension feeders. Assemblages of the sand-dominated facies, with dense shell accumulations of semi-infaunal to epifaunal byssate and infaunal suspension feeders, were formed under shallow, higher energy conditions. Despite the degree of generic endemicity, the mytilids, anomiids, crassateliids, astartids, tellinids, and corbulids are related to the bivalve fauna of the Early Cretaceous Riachuelo Formation of the Sergipe-Alagoas Basin, as previously demonstrated for the bakevelliids and echinoids. Indeed, the Romualdo bivalve fauna is, in part, a modified and impoverished brackish/marine fauna of the Riachuelo Formation.
Mineral-scale insights into the petrogenesis of the 3.30 Ga rhyolite in the Contendas-Mirante region, northern São Francisco Craton, Brazil : implications from results of plagioclase and biotite analyses.
(2023) Farias, Eliana Marinho Branches; Lana, Cristiano de Carvalho; Zincone, Stéfano Albino; Queiroga, Gláucia Nascimento; Graça, Leonardo Martins
The 3.30 Ga high-silica volcanic system of the Gavião Block, São Francisco Craton, represents the remnants of within-plate magmatism related to an intracontinental rift. However, the petrogenetic processes that may have taken place in the relatively shallow primitive continental crust has not been fully constrained due to a scarce record. Petrographic and chemical analyses in biotite, as well as in-situ Sr isotope ratios in plagioclase, were used to trace petrogenetic processes and physicochemical conditions of the magmatic system. The subvolcanic rock has a well-preserved primary volcanic feature represented by magma flow textures, euhedral to subhedral plagioclases, rapakivi microstructures, and glomerocrysts. Plagioclase populations formed at two distinct stages recorded by trace elements and Sr isotope. Plagioclase phenocrysts and rapakivi phenocrysts have a slight enrichment of light rare earth elements (LREE), Sr/Ba ratio, and slight variation of Sr isotopes composition. Meanwhile, other phenocrysts and rapakivi crystals have low LREE, Sr/Ba, and a limited variation of Sr isotope ratio. Mineral chemistry evidence points to country rock assimilation during plagioclase formation and a crustal source for primary biotites under oxidized conditions.
3D geoelectric modeling to characterize ferruginous caves in Brazil, using numerical and physical simulation.
(2024) Cardoso, Luiz Henrique; Bacellar, Luis de Almeida Prado; Oliveira, Nilciléia Cristina de Magalhães; Maciel, Álvaro Simões
In Brazil, the discovery of ferruginous pseudokarst caves in laterite profiles on iron mining areas has been significant. As a result, speleological legislation has restricted mining activity to protect caves considered to be most relevant, however, with subjective criteria. This requires the collection of precise data to better guide them. The application of techniques for the identification and characterization of caves is still limited, due to the irregular topography, vegetation and the obstruction of conduits and saloons by material that fell from the ceiling and walls, and it was also mobilized by miners. A relatively cheap and quick alternative to mapping the caves, compared to classical methods such as boreholes, is Electrical Resistivity (ER). Literature data are apparently controversial, as caves filled with air sometimes have high resistivity (tens to hundreds of thousands of ohms. meter), and sometimes low (up to a few thousand ohms. meter). Thus, the objectives were to investigate the electrical resistivity duality that can be observed in these caves, and present a non-invasive cave mapping methodology and a 3D geoelectric model (inverted), to be used as a reference in future field research. To this end, direct and inverse 3D geoelectrical numerical modeling was carried out to predict the electrical resistivity of typical elements in the ferruginous pseudokarst system of the Quadrilatero ́ Ferrífero (QF), southeast region, where hundreds of caves were cataloged. Field surveys, laboratory analysis of collected material and simulations in a reduced physical model validated the predictions. The results showed that moisture around ferruginous caves can attenuate the electrical signal or even mask the high resistivity of conduits and saloons filled with air. Therefore, it was the main factor considered in the geoelectric model.
Evidence of upwelling on the Brazilian continental shelf of Rio Grande do Norte.
(2023) Nogueira, Mary Lucia da Silva; Eichler, Patrícia Pinheiro Beck; Borges, Miguel Evelim Penha; Rodrigues, André Rosch; Vital, Helenice
This study evaluates Foraminiferal assemblages and their relation with grain size, calcium carbonate content, organic matter, and mineralogy of sediment samples collected at the sediment-water interface along a transect on the northern continental shelf of Rio Grande do Norte State, Brazil, adjacent to the city of Areia Branca. The sedimentary sequence of this shelf is represented by lithostratigraphic units of a marine regressive sequence dominated by four facies: Siliciclastic sand, Silicibioclastic Sand, carbonate mud, and Biosiliciclastic sand. The carbonate content ranged from 5.83% to 85% and the organic matter content from 1.16% to 27.05%. Mineralogical characters separated the predominant siliciclastic content (37% to 92%) from the bioclastic content (8% to 63%). We have identified 14 species out of 50 species of Foraminifera, associated to particular depths and sediment types as follows: (1)deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen (2)the shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica, (3)the central parts of the transect, also in the inner shelf, provide habitats for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata and Buccella peruviana is probably related to colder water temperatures and possibly the occurrence of an upwelling phenomenon for the deepest parts of the area rather than the sedimentological features discussed here.
Dramatic changes in the confluence morphology drived by an extreme hydrologic pulse: impacts to River Doce restoration.
(2024) Marciano, Alexandre Germano; Assireu, Arcilan Trevenzoli; Azevedo, Samara Calçado de; Silva, Benedito Cláudio da; Abreu, Adriana Tropia de; Nalini Júnior, Hermínio Arias
On January 2022, the Carmo River (a tributary of the Doce River) was affected by an extreme hydrological event, with 50-yr return interval. This event was 50% higher than that associated to one of the largest tailing dam failures ever reported that took place in the Gualaxo do Norte River. This delivered to Doce River, through the Carmo River, in a Y-shaped confluence, the contaminated tailing slurry. In order to understand the role of tributaries in the recovery of the Doce River, 2D hydrodynamic and 2D sediment transport models were applied at the confluence of the Carmo River with the Piranga River. Our results, based on hydraulic modeling, remote sensing, and in-situ measurements, indicated that significant amounts of sediments were trapped on the riverbanks and stone banks, making this confluence an important site for the retention of contaminated sediments, influencing sediment budgets and downstream water quality. Therefore, this confluence deserves special attention from water engineering in order to prevent the sediments retained in this area from being transported downstream during extreme events in the coming years. These results can contribute to decision-making, to identify reaches with greater susceptibility to erosion and sediment deposition and to plan the restoration of these rivers.