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Sedimentary Organic Matter Characterization on a Tropical Continental Shelf in Northeastern Brazil

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Document pages: 27 pages

Abstract: In continental shelf areas works where the focus is Geochemistry arewidely relevant, due to the vast complexity and uses of these relief features(social, environmental and economic). On the Brazilian Northeast tropicalshelves, with emphasis on the Pernambuco Continental Shelf (PCS), the publishedstudies are limited and have aimed at portions closer to the coastline. Theobjective of the present work is the description of the characteristics andorigin of sedimentary organic matter (SOM) in the inner and middle Pernambucoshelf, defining and classifying the local geochemical sedimentary facies. Thesampling stations (136) were collected in the study area, and the grain-size,contents of total organic matter (TOM), calcium carbonate (CaCO3)were analyzed. The samples were processed in an elemental analyzer coupled witha mass spectrometer after the elimination of calcium carbonate. The obtaineddata were the grain-size, TOM, CaCO3, elemental (C, N) and thestable isotopic ratios of δ13Ce δ15N of SOM. Based onthe measured values of carbon and nitrogen, the C N ratio, associated to δ13C e δ15N, is observed that in the PCS predominates anorganic matter of marine origin along its entire length: C δ13C > -21 PDB e δ15N > 8Ar. ThePCS presents patches of continental origin SOM, associated to the coastal zonesadjacent to estuarine systems mouths and covering the paleochannels, which mayindicate that this material was carried from the coastal rivers to the offshoreareas, possibly by the paleo-valleys that also act as traps of fine sedimentsand SOM. The statistical analysis indicates the existence of 6 differentsedimentary facies and a prevalence of one of them, characterized bypoorly-sorted bioclastic sandy-gravel, with low to medium organic contents ofmarine origin. This indicates that the coastal sedimentary materialcontributions are low and the local cover is autochthonous of biogenic origin,and deposited according to the surficial topography, morphosedimentary processesand meteoceanographycal conditionings of the study area, typical of moderatehydrodynamic energy environments.

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