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| Ferreira,Ana C.M.; Ferreira,Valderez P.; Soares,Dwight R.; Vilarroel-Leo,Hugo S.. |
| The Alto Quixaba pegmatite, Seridó region, northeastern Brazil, is a 60º/80ºSW-trending subvertical dike discordantly intruded into biotite schists of the Upper Neoproterozoic Seridó Formation. It has three distinct mineralogical and textural zones, besides a replacement body that cuts the pegmatite at its central portion and in which occur, among other gem minerals, colored elbaites. Elbaites usually occur as prismatic crystals, elongate according to the c-axis, with rounded faces and striations parallel to this axis. Optically, crystals are uniaxial negative with strong pleochroism; refractive index extraordinary axis = 1.619-1.622 and ordinary axis = 1.639-1.643, birefringence between 0.019 and 0.021, average relative density of 3.07, and the following... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Elbaite; Tourmaline; Seridó pegmatitic province. |
| Ano: 2005 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000400011 |
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| Pereira,Natan S.; Sial,Alcídes N.; Kikuchi,Ruy K.P.; Ferreira,Valderez P.; Ullmann,Clemens V.; Frei,Robert; Cunha,Adriana M.C.. |
| ABSTRACT Coral skeletons contain records of past environmental conditions due to their long life span and well calibrated geochemical signatures. C and O isotope records of corals are especially interesting, because they can highlight multidecadal variability of local climate conditions beyond the instrumental record, with high fidelity and sub-annual resolution. Although, in order to get an optimal geochemical signal in coral skeleton, sampling strategies must be followed. Here we report one of the first coral-based isotopic record from the Equatorial South Atlantic from two colonies of Porites astreoides from the Rocas Atoll (offshore Brazil), a new location for climate reconstruction. We present time series of isotopic variation from profiles along the... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Coral; Climate change; Rocas Atoll; Carbon and oxygen isotopes; South Atlantic Ocean. |
| Ano: 2015 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652015000501939 |
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| Chiglino,Leticia; Gaucher,Claudio; Sial,Alcides N.; Ferreira,Valderez P.. |
| We report for the first time the occurrence of organic-walled microfossils in Ediacaran limestones and marls of the Frecheirinha Formation, Ubajara Group, and the first Precambrian acritarchs so far reported for northeastern Brazil. The assemblage of the Frecheirinha Formation represents a low-diversity microflora comprising Leiosphaeridia, Lophosphaeridium and subordinated Bavlinella (=Sphaerocongregus). Their thermal alteration index (TAI) between 4+ and 5, suggests metamorphic temperatures exceeding 200-250°C. Higher temperatures are probably related to intruding granitic plutons (Meruoca, Mucambo). Reported δ13C values of carbonates of -3.5 ‰ VPDB (Vienna-Peedee Belemnite) at the base, passing up section into a positive plateau of up to +3.7 ‰, and... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Acritarchs; Ediacaran; Neoproterozoic; Northeastern Brazil. |
| Ano: 2015 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652015000200635 |
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