Isovolumetric weathering and silcrete formation, southern Cape Province, South Africa

✍ Scribed by M. A. Summerfield

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 501 KB
• Volume: 9
• Category: Article
• ISSN: 0360-1269
• DOI: 10.1002/esp.3290090205

✦ Synopsis

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 Si02 to account for observed thicknesses of associated silcrete. Absolute accumulation of SiOz in silcrete is complemented by substantial absolute depletion of AlzOJ. Absolute accumulation of TiOz in both silcrete and associated weathered material together with authigenic anatase concentrations in silctete recorded during micromorphological investigations indicate Ti02 mobilization in a low pH environment (pH < 3.75) during silcrete formation. Under these low pH conditions increased AIZO3 solubility led to replacement of kaolinite and illite by a proportion of Si02 retained in the weathering profile through restricted drainage.