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Isovolumetric weathering and silcrete formation, southern Cape Province, South Africa
Author(s) -
Summerfield M. A.
Publication year - 1984
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.3290090205
Subject(s) - weathering , geology , authigenic , saprolite , kaolinite , bedrock , illite , geochemistry , gibbsite , mineralogy , geomorphology , clay minerals , sedimentary rock
Calculations of absolute elemental gains and losses based on isovolumetric bedrock alteration are applied to deep weathering profiles and silcrete developed on Dwyka Tillite and Bokkeveld Shale. Bedrock weathering to kaolinite and illite yields sufficient SiO 2 to account for observed thicknesses of associated silcrete. Absolute accumulation of SiO 2 in silcrete is complemented by substantial absolute depletion of Al 2 O 3 . Absolute accumulation of TiO 2 in both silcrete and associated weathered material together with authigenic anatase concentrations in silctete recorded during micromorphological investigations indicate TiO 2 mobilization in a low pH environment (pH < 3·75) during silcrete formation. Under these low pH conditions increased Al 2 O 3 solubility led to replacement of kaolinite and illite by a proportion of SiO 2 retained in the weathering profile through restricted drainage.