General aspects of continental margin sediments of the Ceará State, northeast Brazil, from mineralogy and principal component analysis

Journal of the Geological Survey of Brazil

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Site: https://jgsb.cprm.gov.br/index.php/journal/index
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ISSN: 2595-1939
Editor Chefe: Evandro Luiz Klein
Início Publicação: 15/05/2018
Periodicidade: Quadrimestral
Área de Estudo: Multidisciplinar, Área de Estudo: Multidisciplinar

General aspects of continental margin sediments of the Ceará State, northeast Brazil, from mineralogy and principal component analysis

Ano: 2019 | Volume: 2 | Número: 2
Autores: Wanessa S. Marques, Ronaldo G. Bezerra, Daniel P. Souza, George Satander de Sá Freire, Inacio O. de Lima Neto
Autor Correspondente: Wanessa S. Marques | [email protected]

Palavras-chave: pelagic sediments, heavy minerals, marine transgression, PCA analysis

Resumos Cadastrados

Resumo Inglês:

Granulometry, mineralogy, portable X-ray fluorescence (XRFp), portable X-ray diffractometry (XRDp), and
principal component analysis (PCA) have been made in samples of two deep cores of the continental
margin of the Ceará State, northeast Brazil, aiming to detail the general aspects of deep sedimentation,
including mechanical dispersion of continental minerals, environmental chemistry, and clay identification.
The samples comprised biogenic oozes, clays, coarse silt, and fine sand to a lesser extent. The granulometric
composition suggests slow and calm sediment accumulation over time. XRDp analysis pointed out that
pelagic clays consist of chlorite, kaolinite, nontronite, and vermiculite. High oxidation levels are suggested
for the two core samples, represented by the light brown color 5YR 6/4 of the sediments. Traces of minerals
existing at the continental shelf were found, although in the core SIS-454 at 160 to 164 cm depth, there is
a total absence of both heavy and light continental minerals. In core SIS-515, the total absence of heavy
and light minerals was found at the depth of 87 to 92 cm. The levels with absence of continental minerals
are probably associated with the absence of mechanical dispersion due to transgression and regression
events in the Ceará continental shelf. The high oxidation levels can probably be linked to shallow waters
caused by sea level changes, or to large period of sedimentation in the slope. From the statistical analysis,
it is suggested that element contents are related to each other according to the provenance setting, whereas
the pelagic sediment has provenance from marine water, resurgence currents, wind transport, cosmic
dust, and from slow transportation, originated from the continent. It was deduced that sedimentation in the
area was affected by at least two events with absence of mechanical dispersion of continental sediments,
associated with geochemical characteristics represented by antagonism between elements of terrigenous
and biogenic origin. These events are possibly associated with small-scale regressions occurred during
the Flandrian Transgression in the Ceará Basin.