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Cosmogenic 32 Si as a tracer of biogenic silica burial and diagenesis: Major deltaic sinks in the silica cycle
Author(s) -
Rahman S.,
Aller R. C.,
Cochran J. K.
Publication year - 2016
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl069929
Subject(s) - authigenic , diagenesis , geology , biogenic silica , weathering , geochemistry , dissolved silica , mineralogy , paleontology , dissolution , sediment , chemistry
Measurements of natural cosmogenic 32 Si ( t 1/2 ~ 140 years) in tropical deltaic sediments demonstrate for the first time that most 32 Si is present in rapidly formed authigenic clays and not biogenic opaline silica (bSi). The burial of bSi in deltaic and continental margin sediments has likely been greatly underestimated because of diagenetic alteration of bSi to clay, little of which dissolves in the classically used operational bSi leach. Rapid reverse weathering reactions during early diagenesis must be considered as a significant pathway of reactive Si storage in deltaic deposits. Based on 32 Si, actual storage may be 2–3 times the best recent estimates extrapolated from diagenetic models or attempts to modify operational bSi methods to include authigenic clay (~900 µmol/g versus ~250 µmol/g). Measurements of natural 32 Si inventories in sediments and initial specific activities in biogenic silica provide a means to independently constrain the marine Si cycle.