首页|Revisiting the Mg isotopic systematics of siliciclastic components of sediments and sedimentary rocks:A new geochemical proxy of continental weathering in Earth's history
Revisiting the Mg isotopic systematics of siliciclastic components of sediments and sedimentary rocks:A new geochemical proxy of continental weathering in Earth's history
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The Mg isotopic compositions of siliciclastic components(δ26Mgsili)of sediments and sedimentary rocks have been commonly used to constrain the intensity of continental weathering,based on observations of,(1)an upward enrichment of 26Mg in modem weathering profiles,(2)preferential uptake of 26Mg in soil clays,and(3)general positive correlations between weathering intensities and δ26Mgsili values.However,not all weathering profiles display an upward increase of δ26Mgsi)i,and not all soil clays enrich in 26Mg,complicating the interpretations of δ26Mgsili data of sediments and sedimentary rocks.To further explore the controls of δ26Mgsili of sediments and sedimentary rocks,here we measured δ26Mgsili,mineralogical compositions and major element compositions of deep sea sediments from South China Sea(SCS)and carbonate rock samples from two late Paleozoic sections in South China.Carbonate samples show decreasing trends of both normalized Mg concentration(Mgnorm)and δ26Mgsili values with the increase of weathering intensity,while SCS sediments samples do not show any correlation between Mgnorm or δ26Mgsili values and weathering intensity.A three-stages weathering model is developed to explain the observed Mgnorm and δ26Mgsili data.In the new model,weathering can be divided into three stages,(1)the preliminary weathering stage characterized by dissolution of primary minerals and formation of secondary clay minerals in saprolite,(2)the transitional stage with massive vermiculite and chlorite formation on the bottom of soil,and(3)the advanced stage showing dissolution of vermiculite and chlorite in the top of soil.The new model explains an δ26Mgsili increase and Mgnom decrease with an increase weathering intensity in preliminary weathering stage and decrease of Mgnorm and δ26Mgsili with increase weathering intensity in advanced weathering stage.The revised weathering model warrants the application of Mg isotope in the study of continental weathering in deep time.
Clay mineralChemical weatheringCIASoilWeathering model
Key Laboratory of Orogenic Belt and Crustal Evolution,MOE
School of Earth and Space Sciences,Peking University Beijing 100871,China
State Key Laboratory of Continental Dynamics,Shaanxi Key Laboratory of Early Life and Environments,Department of Geology,Northwest University,Xi'an 710069,China
Institute of Sedimentary Geology Chengdu University of Technology,Chengdu 610059,China
Key Laboratory of Rhenium-Osmium Isotopic Geochemistry,Chinese Academy of Geological Sciences,Beijing 100037,China
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National Key Research and Development ProgramNational Key Research and Development ProgramNational Natural Science Foundation of China
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