Egberto Pereira

SILURIAN AND LOWER DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF THE PARANÁ BASIN IN BRAZIL AND PARAGUAY

Abstract The taxonomy and distribution of Chitinozoa from Silurian (Llandovery) and Lower Devonian strata are reported from the Parana Basin in southern Brazil and eastern Paraguay. The pre‐Carboniferous sequences of the Parana Basin in this area are present in three sub‐basins viz., the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in east Paraguay. There is more similarity in the lithology between the Alto Garcas and “East Paraguay”; sub‐basins, than between the former and the Apucarana sub‐basin. Llandoverian and Lochkovian to Pragian beds are present in all sub‐basins. So far, no Emsian beds have been found in outcrops from the north‐northwest margin of the Alto Garcas Sub‐basin, and no early Emsian beds in the outcrops on the northeast margin. Furthermore, Emsian beds could not be identified from the “East Paraguay Sub‐basin”; in the present study. The Early Devonian sequence is more complete in the Apucarana Sub‐basin. It seems that the Apucarana ...

An Early Devonian flora, including Cooksonia from the Paraná Basin (Brazil)

We report here the presence of an extensive flora from an early Lochkovian (Lower Devonian: ∼406 million years) locality in the Parana Basin (Brazil). The exceptional macrofossil assemblage includes several hundred specimens of a new Cooksonia species, and representatives of 10 other taxa, 5 of which at least are new. This plant assemblage illustrates the amplitude of the Siluro-Devonian land plant primary radiation. During the Lochkovian, the Parana Basin was positioned in southern Gondwana, within the southern polar circle. The occurrence of this rich plant assemblage substantiates the hypotheses of a Warm Mode and of an ice-free southern pole during the earliest Devonian. Some taxa exhibit characters interpreted as potentially related to cold hardiness: embedding of the sporangium within the axis, abundance of emergences, dense branching, and protection of the apical meristem.

Environmental Quality Assessment of Bizerte Lagoon (Tunisia) Using Living Foraminifera Assemblages and a Multiproxy Approach

This study investigated the environmental quality of the Bizerte Lagoon (Tunisia) through an integrated approach that combined environmental, biogeochemical, and living benthic foraminiferal analyses. Specifically, we analyzed the physicochemical parameters of the water and sediment. The textural, mineralogical, and geochemical characteristics of the sediment, including total organic carbon, total nitrogen, simultaneously extracted metals (SEM), acid volatile sulfides (AVS), chlorophyll a, CaCO3, and changes in bacterial populations and carbon isotopes were measured. The SEM/AVS values indicated the presence of relatively high concentrations of toxic metals in only some areas. Foraminiferal assemblages were dominated by species such as A. parkinsoniana (20–91%), Bolivina striatula (<40%), Hopkinsina atlantica (<17%), and Bolivina ordinaria (<15%) that cannot be considered typical of impacted coastal lagoons both in Mediterranean and northeast Atlantic regions. The results of this work suggest that Bizerte Lagoon is a unique setting. This lagoon is populated by typical marine species that invaded this ecosystem, attracted not only by the prevailing favorable environmental conditions but also by the abundance and quality of food. The results indicate that the metal pollution found in some areas have a negative impact on the assemblages of foraminifera. At present, however, this negative impact is not highly alarming.

MIDDLE AND UPPER DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF THE PARANÁ BASIN IN BRAZIL AND PARAGUAY

Abstract Chitinozoans from Middle and Upper Devonian strata have been investigated from the Parana Basin in southern Brazil and eastern Paraguay. These sequences are present in the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in eastern Paraguay. Marine communication between the sub‐basins was established during the early Givetian. Of the 49 chitinozoan species encountered, 28 species are retained in open nomenclature, and Ancyrochitina simplex is newly described. A chitinozoan biozonation, with five zones, is proposed for the investigated interval. The zones are from oldest to youngest: concurrent range zone of Alpenachitina eisenacki and Spinachitina biconstricta (late Eifelian?‐early Givetian); the interval range zone of Ancyrochitina taouratinensis (latest early‐middle Givetian); concurrent range zone of Fungochitina pilosa and Ancyrochitina langei (late Givetian); concurrent range zone of Hoegisphaera glabra and Ramochitina derbyi (early Frasnian)...

Organic matter quantity and quality, metals availability and foraminiferal assemblages as environmental proxy applied to the Bizerte Lagoon (Tunisia).

This study analyzes the benthic trophic state of Bizerte Lagoon (Tunisia) based on the total organic matter and the bioavailability of biopolymeric carbon including proteins (PTN), carbohydrates (CHO), lipids (LIP), chlorophyll a, as well as bacteria counts. The overall simultaneously extracted metals (SEM), and acid volatile sulfides (AVS) as well as the SEM/AVS ratio indicative of the toxicity of the sediments also were analyzed aiming to study their impact in the dimension, composition and structure of both dead and living benthic foraminiferal assemblages. In the studied sites TOC content is relatively high and the PTN/CHO values indicate that they can be considered as meso-eutrophic environments. The CHO/TOC and C/N values suggest that the OM which accumulated on the sediments surface has mainly natural origin despite the introduction of municipal and industrial effluents in the lagoon and the large bacterial pool. The living assemblages of benthic foraminifera of Bizerte Lagoon are quite different to other Mediterranean transitional systems studied until now. They are composed of typical lagoonal species but also include several marine and opportunistic species including significant numbers of bolivinids, buliminids, Nonionella/Nonionoides spp. and Cassidulina/Globocassidulina spp. These assemblages seem to benefitfrom the physicochemical parameters and the sediment stability. They may however face environmental stress in the lagoon related to the AVS production as a result of the organic matter degradation and toxicity in some areas due to the available concentrations of metals. Nonetheless statistical results evidence that the structure and dimension of assemblages are being controlled mostly by OM quantity and quality related mainly to the availability of PTN, CHO and chlorophyll a. Results of this work support the importance of considering OM quantity and quality in studies of environmental impact in coastal systems.

Biochemical Composition and Foraminiferal Content of Sediments for Determining Bottom Sector Environments in Guanabara Bay (Rio de Janeiro, Brazil)

ABSTRACT Clemente, I.M.M.M.; da Silva, F.S.; Laut, L.L.M.; Frontalini, F.; da Costa, V.L.; da Conceição Rodrigues, M.A.; Pereira, E.; Bergamaschi, S.; Filho, J.G.M., and Martins, M.V.A., 2015. Biochemical composition and foraminiferal content of sediments for determining bottom sector environments in Guanabara Bay (Rio de Janeiro, Brazil). Three cities in Brazil—Rio de Janeiro, Niterói, and São Gonçalo—with an estimated total population of 11 million people, are located in the surroundings of Guanabara Bay (RJ-Brazil), making it a highly contaminated coastal system. Because of its importance, Guanabara Bay has been one of the most studied coastal environments in Brazil. Despite that, this study represents the first investigation, to our knowledge, to couple benthic foraminifera with the quantity and quality of organic matter in the area. The spatial distribution of water salinity and the surface sediment reduction potential, grain size, total organic carbon, sulfur, bacterial organic carbon, biopolymers such as carbohydrates, proteins, lipids, bacterial enzyme esterase, and total foraminiferal assemblages were studied at 30 stations in Guanabara Bay. Based on these data, six bottom environments—industrial, marginal urban, marginal urban/industrial mixing, eutrophic, transitional, and outer— were identified and described.

Large-scale sill emplacement in Brazil as a trigger for the end-Triassic crisis

The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO2. In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206Pb/238U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.

Influence of dominant wind patterns in a distal region of the NW Iberian Margin during the last glaciation

This work combines planktonic foraminiferal assemblages, stable isotope, transfer function estimated sea surface paleotemperatures (SST) and export productivity (Pexp) with sedimentological records from the PC7 core to document paleoclimatic and paleoceanographic changes on a distal region of the NW Iberian Margin since the last glaciation (<≈68 ka). Neodymium and strontium isotope data are also used to identify the provenance of ice rafted debris (IRD) during Heinrich event 5 (H5). Our results are compared and combined with previously published records and evidence that melt water and icebergs from the Canada, Greenland, Iceland and Europe ice sheets arrived to the NW Iberian Margin causing a significant decrease of SST during the last six Heinrich Stadials (HS) and some Dansgaard–Oeschger (D-O) stadial events. εNd and 87Sr/86Sr indicate that the studied locality mostly received sediments from European Ice Sheets (EIS) during H5. During the HS and D–O stadial events, SSTs were in general higher than in other cores collected in inner areas of the NW Iberian Margin. The presence and intensification of Portugal Current probably induced heat transfer to this distal region of the Iberian Margin. Our results also suggest the occurrence of high variability in the intensity and wind patterns during the last glaciation. In some periods, the intensity of northerly winds could have been very strong and contributed to a significant stimulation of ocean productivity in this distal area through the intensification of upwelling. In general, oceanic productivity decreased during the HS and D–O as the presence of cold and less saline water prevented nutrient rich waters from deep levels reaching the surface. The high productivity events were bracketed by periods characterized by the highest influence of the Azores Current eastern branch during which northerly winds and the oceanic productivity should have been weakened. Supplementary material: Geochemical and foraminiferal data analysed in this work as well as Pearson Correlations between the analysed data are available at https://doi.org/10.6084/m9.figshare.c.3931813