Sulfur diagenesis and burial on the Amazon shelf: Major control by physical sedimentation processes |
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Authors: | Robert C Aller Neal E Blair |
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Institution: | (1) Marine Sciences Research Center, State University of New York, 11794-5000 Stony Brook, New York, USA;(2) Marine, Earth, and Atmospheric Sciences, North Carolina State University, 27695-8208 Raleigh, North Carolina, USA |
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Abstract: | Early diagenetic properties of Amazon shelf muds are dominated by nonsulfidic Fe and Mn cycling, resulting in relatively little S deposition compared to previously studied marine margin environments. Despite abundant potential reactants typical of sulfidic deposits, authigenic sulfides represent only ~ 10% of diagenetically reduced Fe, and DOP (degree of pyritization) is only ~0.02. The average C/S (wt wt–1) ratio of buried sediment below the zone of SO4
2- reduction is ~ 7.4, ~ 2.6 times more than the commonly assumed modern shelf average of ~ 2.8. The deltaic burial rate for S is ~ 0.65 × 106 tons yr–1. Relatively low S deposition is promoted by terrestrial weathering that delivers reactive oxide debris, but apparently depends most strongly on reoxidation and rapid burial by intense physical reworking and fluid-mud formation. Diagenetic models of S distributions demonstrate rapid sediment reworking (~ 10–100 cm yr–1 as apparent advection), substantial S reoxidation (84–98%), and in one case, massive sediment deposition of up to ~ 5 m of sediment in ~ 1 year. Extremely low DOP coupled with dominance by nonsulfidic reduced-Fe minerals and lack of biogenic sedimentary structures may be an indicator in marine organic-rich muds of intense physical reworking under oxygenated waters. |
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