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Pyritization of Iron in Sediments from the Continental Slope of the Northern Gulf of Mexico
Authors:John W Morse  Dwight K Gledhill  Karen S Sell  Rolf S Arvidson
Institution:(1) Department of Oceanography, Texas A & M University, College Station, TX, 77843;(2) Department of Earth Science, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251, USA
Abstract:In sediments from the continental slope of the Northern Gulf of Mexico, generally,the degree of iron pyritization (DOP) is low (<0.1) and dissolved sulfide is belowdetection limits (sim5 mgrM), whereas dissolved Fe is typically about 50 to100 mgrM. Therefore, the dissolution of kinetically reactive iron minerals generallydominates over the rate of sulfide production in sediments throughout this region.However, in sediments where hydrocarbons have been added via seepage from thesubsurface, dissolved-Fe is undetectable, DOP can approach 1, and high concentrationsof dissolved sulfide (up to sim11 mM) are commonly present. Even though thesesediments have high total reduced sulfide (TRS) concentrations (typically 150 to370 mgrmol gdw-1), their average C/S ratio is about 4 times that of ldquonormalrdquo marine sediments reflecting the major input of hydrocarbons. DOP is significantly (sim20%) higher when calculated using reactive-Fe extracted by citrate dithionite than by cold 1N HCl. This difference is primarily due to the greater extraction efficiency of the cold HCl method for silicate-Fe. TRS tends to rise to a maximum, and remains close to constant even at high (mM) dissolved sulfide concentrations. These TRS concentrations, therefore, represent the size of the ``kinetically' reactive-Fe pool during early diagenesis.
Keywords:iron  sulfides  sediments  kinetics  Gulf of Mexico
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