Chemostratigraphy of the Carajás banded iron formation, Brazil : a record of Neoarchean Ocean chemistry

Martins, Pedro Luiz Gomes; Toledo, Catarina Labouré Bemfica; Silva, Adalene Moreira; Chemale Junior, Farid; Arche, Corey; Assis, Luciano M. de

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Campo DC	Valor	Idioma
dc.contributor.author	Martins, Pedro Luiz Gomes	-
dc.contributor.author	Toledo, Catarina Labouré Bemfica	-
dc.contributor.author	Silva, Adalene Moreira	-
dc.contributor.author	Chemale Junior, Farid	-
dc.contributor.author	Arche, Corey	-
dc.contributor.author	Assis, Luciano M. de	-
dc.date.accessioned	2022-08-10T10:47:35Z	-
dc.date.available	2022-08-10T10:47:35Z	-
dc.date.issued	2022	-
dc.identifier.citation	MARTINS, Pedro L. G. et l. Chemostratigraphy of the Carajás banded iron formation, Brazil : a record of Neoarchean Ocean chemistry. Gondwana Research, [S.l.], v. 105, p. 217-242, maio 2022. DOI: https://doi.org/10.1016/j.gr.2021.09.008.	pt_BR
dc.identifier.uri	https://repositorio.unb.br/handle/10482/44473	-
dc.language.iso	Inglês	pt_BR
dc.publisher	Elsevier B.V.	pt_BR
dc.rights	Acesso Restrito	pt_BR
dc.title	Chemostratigraphy of the Carajás banded iron formation, Brazil : a record of Neoarchean Ocean chemistry	pt_BR
dc.type	Artigo	pt_BR
dc.subject.keyword	Quimiostratigrafia	pt_BR
dc.subject.keyword	Província Carajás	pt_BR
dc.subject.keyword	Isótopos	pt_BR
dc.subject.keyword	Ferro	pt_BR
dc.identifier.doi	https://doi.org/10.1016/j.gr.2021.09.008	pt_BR
dc.relation.publisherversion	https://www.sciencedirect.com/science/article/pii/S1342937X2100263X?via%3Dihub	pt_BR
dc.description.abstract1	One of the most important occurrences of banded iron formation (BIF) worldwide is situated in the Carajás Mineral Province, southeastern Amazonian Craton. The BIFs are jaspilites and are hosted in the Neoarchean ( 2.74 Ga) volcano-sedimentary sequence of the Grão-Pará Group. They are mostly composed of cm-thick intercalations of hematite, jasper, and chert. Their primary textures and structures are still preserved, which make them an ideal archive to evaluate the paleomarine environment. Low abundance of Al2O3 (<1.0 wt%) and HFSE (<1 ppm) for most BIF samples indicate an essentially detritus-free depositional environment. Overall, the rare earth elements and yttrium (REY) patterns show a weak positive lanthanum (La) anomaly, and a pronounced positive europium (Eu) anomaly (Eu/EuPAAS = 1.86 – 5.05), although the presence of true cerium (Ce) anomaly is not evident. Stratigraphic variations in iron isotope compositions, up to 0.80‰ (d56Fe = +1.10 to +1.90‰) over tens to hundreds of meters of stratigraphic section, point to relative changes in the iron isotope composition of Carajás seawater over periods of a few million years. The jaspilites show heterogeneous distribution of Nd isotopic signature throughout the BIF sequence, and rocks from near the basaltic flows/jaspilite contact (type-II) have negative eNd (t) values (–4.97 to –0.90). In contrast, predominantly positive eNd(t) values (–0.84 to +5.40) are common in the remaining samples (type-I). The strongly positive d56Fe values indicate a low degree of partial oxidation of Fe(II), which, combined with the pronounced positive Eu anomalies and the absence of Ce anomalies, hint towards that the deposition occurred mainly on a deep-sea environment with intense hydrothermal activity under anoxic and suboxic conditions, distal to continental landmasses. Locally, considerable oxygen was probably present in the ancient ocean’s water masses, which led to the precipitation of BIFs.	pt_BR
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