scholarly journals Chemostratigraphy of the lower Bambuí Group, southwestern São Francisco Craton, Brazil: insights on Gondwana paleoenvironments

2016 ◽  
Vol 46 (suppl 1) ◽  
pp. 145-162 ◽  
Author(s):  
Matheus Kuchenbecker ◽  
Marly Babinski ◽  
Antônio Carlos Pedrosa-Soares ◽  
Leonardo Lopes-Silva ◽  
Felipe Pimenta
Keyword(s):  
Biological Activity ◽  
Chemical Weathering ◽  
Southeastern Brazil ◽  
Sudden Increase ◽  
Freshwater Input ◽  
Isotopic Signatures ◽  
Mountain Ranges ◽  
Cap Carbonate ◽  
Carbonate Deposition ◽  
Regional Tectonic

ABSTRACT: The Bambuí Group, the most extensive carbonate-siliciclastic cover on the São Francisco craton, has been a matter of debate because of its potential correlations to global glacial events. Unfortunately, most available chemostratigraphic data came from samples collected on surface rock exposures, ever susceptible to the aggressive chemical weathering that characterizes the southeastern Brazil. On the other hand, we present here high-resolution chemostratigraphic studies based on C, O and Sr isotopic data from 53 samples collected along a weathering-free, continuous, 175 m thick sedimentary succession. This succession was recovered by borehole drilling in the southwestern São Francisco craton, where occur the Carrancas and Sete Lagoas formations, the lowermost units of the Bambuí Group. The drill cores reveal extremely irregular contacts between the basal diamictite and its basement, an Archaean foliated granodiorite. Geochronological and sedimentological data strongly suggest that the diamictite represents a lodgement till. This glaciogenic deposit is covered by a limestone succession which starts with impure carbonates showing aragonite pseudomorph fans and thin bands of black shale. The limestone pile grades to a marl-mudstone interval, which turns to a carbonate with biological components, succeeded by stromatolitic dolomite at the top. C and O isotopic signatures (referred to V-PDB) allow to the subdivision of the lower carbonate-pelite section into three intervals. The first isotopic interval corresponds to a cap carbonate, and displays negative values of δ13C (c . -4‰), and a large oscillation of the δ18O (-6 to -15‰). The Interval II shows a striking homogeneity in δ13C and δ18O, around 1‰ and -7‰, respectively. At the top, Interval III shows a large positive excursion of the δ13C (up to 8‰) and δ18O (-8 to -3‰) values. Unaltered 86Sr/87Sr ratios range from 0.7075 to 0.7077, mainly at the top of the section. The geochemistry of the carbonates is controlled by their terrigenous content (mostly quartz and clay minerals) which is concentrated in the lower units. Samples free of terrigenous contamination show Y/Ho ratios ranging from 25 to 50, suggesting a freshwater input during carbonate deposition. It is concluded that the diamictite has a glaciogenic origin and is covered by a cap carbonate. This pair has been identified along the basin and is related to one of the main Neoproterozoic glaciations. Discrepancy between the 86Sr/87Sr values and the global variation curves can be related to freshwater input during the carbonate deposition. Based on the regional tectonic context, the Bambuí Basin may have been a restricted marine basin, totally or partially surrounded by mountain ranges within Gondwana, in the Neoproterozoic/Paleozoic boundary. In its early stages, the sedimentation was influenced by a global glacial event, whose melting phase was responsible by freshwater input in the basin. The gradual rise of the temperature was followed by an increase of the biological activity. Finally, a sudden increase in the biological activity could have been driven by paleogeographic changes caused by the active tectonic.

scholarly journals Episode of intense chemical weathering during the termination of the 635 Ma Marinoan glaciation

2016 ◽  
Vol 113 (52) ◽  
pp. 14904-14909 ◽  
Author(s):  
Kang-Jun Huang ◽  
Fang-Zhen Teng ◽  
Bing Shen ◽  
Shuhai Xiao ◽  
Xianguo Lang ◽  
...  
Keyword(s):  
South China ◽  
Chemical Weathering ◽  
Snowball Earth ◽  
Carbonate Precipitation ◽  
Isotopic Data ◽  
Low Intensity ◽  
Cap Carbonates ◽  
Cap Carbonate ◽  
Carbonate Deposition ◽  
Global Precipitation

Cryogenian (∼720–635 Ma) global glaciations (the snowball Earth) represent the most extreme ice ages in Earth’s history. The termination of these snowball Earth glaciations is marked by the global precipitation of cap carbonates, which are interpreted to have been driven by intense chemical weathering on continents. However, direct geochemical evidence for the intense chemical weathering in the aftermath of snowball glaciations is lacking. Here, we report Mg isotopic data from the terminal Cryogenian or Marinoan-age Nantuo Formation and the overlying cap carbonate of the basal Doushantuo Formation in South China. A positive excursion of extremely high δ26Mg values (+0.56 to +0.95)—indicative of an episode of intense chemical weathering—occurs in the top Nantuo Formation, whereas the siliciclastic component of the overlying Doushantuo cap carbonate has significantly lower δ26Mg values (<+0.40), suggesting moderate to low intensity of chemical weathering during cap carbonate deposition. These observations suggest that cap carbonate deposition postdates the climax of chemical weathering, probably because of the suppression of carbonate precipitation in an acidified ocean when atmospheric CO2 concentration was high. Cap carbonate deposition did not occur until chemical weathering had consumed substantial amounts of atmospheric CO2 and accumulated high levels of oceanic alkalinity. Our finding confirms intense chemical weathering at the onset of deglaciation but indicates that the maximum weathering predated cap carbonate deposition.

How tillite weathering during the snowball Earth aftermath induced cap carbonate deposition

Geology ◽  
2012 ◽  
Vol 40 (11) ◽  
pp. 1027-1030 ◽  
Author(s):  
Sébastien Fabre ◽  
Gilles Berger
Keyword(s):  
Snowball Earth ◽  
Cap Carbonate ◽  
Carbonate Deposition

scholarly journals Chemical weathering rates and atmospheric/soil CO2 consumption of igneous and metamorphic rocks under tropical climate in southeastern Brazil

2016 ◽  
Vol 443 ◽  
pp. 54-66 ◽  
Author(s):  
Alexandre Martins Fernandes ◽  
Fabiano Tomazini da Conceição ◽  
Eder Paulo Spatti Junior ◽  
Diego de Souza Sardinha ◽  
Jeferson Mortatti
Keyword(s):  
Chemical Weathering ◽  
Tropical Climate ◽  
Southeastern Brazil ◽  
Metamorphic Rocks ◽  
Soil Co2 ◽  
Weathering Rates ◽  
Co2 Consumption

Trace and rare earth elemental investigation of a Sturtian cap carbonate, Pocatello, Idaho: Evidence for ocean redox conditions before and during carbonate deposition

2012 ◽  
Vol 192-195 ◽  
pp. 89-106 ◽  
Author(s):  
Edward E. Meyer ◽  
Andrew N. Quicksall ◽  
Joshua D. Landis ◽  
Paul K. Link ◽  
Benjamin C. Bostick
Keyword(s):  
Rare Earth ◽  
Redox Conditions ◽  
Cap Carbonate ◽  
Carbonate Deposition

scholarly journals Rapid enhancement of chemical weathering recorded by extremely light seawater lithium isotopes at the Permian–Triassic boundary

2018 ◽  
Vol 115 (15) ◽  
pp. 3782-3787 ◽  
Author(s):  
He Sun ◽  
Yilin Xiao ◽  
Yongjun Gao ◽  
Guijie Zhang ◽  
John F. Casey ◽  
...  
Keyword(s):  
Mass Extinction ◽  
Chemical Weathering ◽  
Triassic Boundary ◽  
Isotopic Signatures ◽  
Siberian Traps ◽  
Li Isotope ◽  
Continental Weathering ◽  
Excessive Nutrients ◽  
Permian Mass Extinction ◽  
Permian Triassic Boundary

Lithium (Li) isotope analyses of sedimentary rocks from the Meishan section in South China reveal extremely light seawater Li isotopic signatures at the Permian–Triassic boundary (PTB), which coincide with the most severe mass extinction in the history of animal life. Using a dynamic seawater lithium box model, we show that the light seawater Li isotopic signatures can be best explained by a significant influx of riverine [Li] with light δ7Li to the ocean realm. The seawater Li isotope excursion started ≥300 Ky before and persisted up to the main extinction event, which is consistent with the eruption time of the Siberian Traps. The eruption of the Siberian Traps exposed an enormous amount of fresh basalt and triggered CO2 release, rapid global warming, and acid rains, which in turn led to a rapid enhancement of continental weathering. The enhanced continental weathering delivered excessive nutrients to the oceans that could lead to marine eutrophication, anoxia, acidification, and ecological perturbation, ultimately resulting in the end-Permian mass extinction.

scholarly journals Records of the Ornate Hawk-eagle, Spizaetus ornatus (Daudin, 1800) (Accipitridae), from the state of São Paulo, southeastern Brazil

Check List ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 651-655
Author(s):  
Vagner Cavarzere ◽  
Gustavo Muniz ◽  
Paulo Antonio Silva ◽  
Wilton Felipe Teixeira
Keyword(s):  
Atlantic Forest ◽  
Sao Paulo ◽  
The State ◽  
Southeastern Brazil ◽  
São Paulo ◽  
The West ◽  
Fragmented Landscapes ◽  
Mountain Ranges ◽  
Neighboring State ◽  
Coastal Mountain

We review the distribution of the Ornate Hawk-eagle, Spizaetus ornatus (Daudin, 1800), in the state of São Paulo, reporting localities with records of the species. Most locations where the species has been historically documented have no recent records, especially to the west of the large remnants of forest in the coastal mountain ranges. Most current records come from Serra de Paranapiacaba, southwestern São Paulo, whereas no records exist within the Cerrado domain. Unlike the neighboring state of Minas Gerais, where it is found in fragmented landscapes, in São Paulo, the species occurs exclusively within protected areas in large blocks of Atlantic Forest.

Remarks on “A new Phyllomedusa Wagler (Anura, Hylidae) with reticulated pattern on flanks from Southeastern Brazil”

Zootaxa ◽  
2009 ◽  
Vol 2044 (1) ◽  
pp. 61-64 ◽  
Author(s):  
REUBER ALBUQUERQUE BRANDÃO ◽  
GUILHERME FAJARDO R. ÁLVARES
Keyword(s):  
New Species ◽  
Original Description ◽  
Ventral Surface ◽  
Species Group ◽  
Southeastern Brazil ◽  
Eyes Absent ◽  
Characteristic Distribution ◽  
Mountain Ranges ◽  
Upper Jaw

Some species in the Phyllomedusa hypochondrialis species group have a reticulated pattern on the hidden parts of the flanks and limbs. These species are quite interesting given their characteristic distribution on mountain ranges, reproduction occurring in streams and rivulets, and by the surprising richness of the group. Four new species of Phyllomedusa were described in the last five years; three were species with reticulated pattern on flanks, endemic to restricted mountain ranges (Brandão 2002, Caramaschi et al., 2006, Giaretta et al., 2007). The most recently described species is Phyllomedusa araguari (Giaretta et al., 2007). However, some information reported in this description in relation to the original description of Phyllomedusa oreades (Brandão 2002) deserves further comments. Phyllomedusa araguari was described based on only three individuals and the authors stated that it can be easily distinguished from the very similar P. oreades by: 1) the presence of a reticulated pattern bordering the upper jaw and encircling the eyes (absent in P. oreades), 2) by having a broader reticulated strip in flanks, 3) a well defined reticulated pattern on throat, belly and ventral surfaces of limbs, 4) less projected nostrils, and 5) white ventral surface in life (pink in P. oreades). Phyllomedusa araguari was also reported as a pond breeder, while P. oreades is a stream breeder.

Paratelmatobius mantiqueira Pombal & Haddad, 1999 (Anura: Leptodactylidae): New specimens and rectification of the type locality of a rare species from the Serra da Mantiqueira, southeastern Brazil

Zootaxa ◽  
2020 ◽  
Vol 4845 (3) ◽  
pp. 447-450
Author(s):  
ELSIE ROTENBERG ◽  
EDELCIO MUSCAT ◽  
DANIEL RODRIGUES STUGINSKI ◽  
LUÍS FELIPE TOLEDO ◽  
MATHEUS DE TOLEDO MOROTI
Keyword(s):  
Atlantic Forest ◽  
Rare Species ◽  
Type Locality ◽  
Southeastern Brazil ◽  
Congeneric Species ◽  
Small Areas ◽  
Serra Do Mar ◽  
Mountain Ranges ◽  
Type Series ◽  
Species Type

There are currently seven species of small frogs (up to 30 mm in snout-vent length) in the genus Paratelmatobius Lutz & Carvalho 1958 (Frost, 2020). They are all endemic to mountain ranges in the Atlantic Forest, occurring in the Serra do Mar and Serra da Mantiqueira, southeastern Brazil (Santos et al. 2019). Most congeneric species are considered rare and their distribution is restricted to small areas (Domenico et al. 2014; Santos et al. 2020). Paratelmatobius mantiqueira Pombal & Haddad 1999 is one of the most enigmatic species in the genus. It hadn’t been seen from 1953, when the type series was collected, until 2005, when one specimen was found in the municipality of Resende, state of Rio de Janeiro (Vrcibradic et al. 2010). Recently, we found a new population of P. mantiqueira in the state of São Paulo. While reviewing the scattered information available about the species, we noticed inconsistencies related to the species’ type locality. We propose its rectification in this manuscript. 

Use of isotopic signatures to assess the food web in a tropical shallow marine ecosystem of Southeastern Brazil

2006 ◽  
Vol 40 (3) ◽  
pp. 381-390 ◽  
Author(s):  
T.N. Corbisier ◽  
L.S.H. Soares ◽  
M.A.V. Petti ◽  
E.Y. Muto ◽  
M.H.C. Silva ◽  
...  
Keyword(s):  
Food Web ◽  
Marine Ecosystem ◽  
Southeastern Brazil ◽  
Shallow Marine ◽  
Isotopic Signatures

scholarly journals Seasonal chaetognath abundance and distribution in a tropical estuary (Southeastern, Brazil)

2005 ◽  
Vol 53 (1-2) ◽  
pp. 47-53 ◽  
Author(s):  
Luiz Loureiro Fernandes ◽  
José Mauro Sterza ◽  
Keyla de Oliveira Neves
Keyword(s):  
Dominant Species ◽  
High Salinity ◽  
Tidal Effect ◽  
Southeastern Brazil ◽  
Estuarine System ◽  
Tropical Estuary ◽  
Freshwater Input ◽  
Wet Season ◽  
Outer Estuary ◽  
Abundance And Distribution

This study focuses on the seasonal variation of the chaetognath species in the Vitória Bay/Passage Channel estuarine system, Espírito Santo, Brazil, in terms of their abundance and distribution. Specimens of chaetognaths were collected between July 1997 and April 1998 at 10 sampling stations, with a cylindrical-conical plankton net of 200 µm mesh and 30 cm mouth, fitted with a mechanical flowmeter. Five chaetognath species were identified: Sagitta enflata, Sagitta decipiens, Sagitta hispida, Sagitta friderici and Sagitta minima. Most of them were distributed in areas of high salinity (e.g. at the stations closest to the outer estuary). The dominant species, S. enflata and S. friderici, were more frequent in the outer estuary where salinities varied from 32 (wet season - summer) to 28 (dry season - winter). S. friderici was the only species found right in the middle of the Passage Channel, at a station close to the main freshwater input into the estuary. Results showed that chaetognaths only enter the estuary due to the tidal effect, and that they are not typical residents of this system. This is to be expected because the group normally inhabits only truly marine regions.

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