Saprolite-Bauxite Facies of Ferralitic Duricrusts on Palaeosurfaces of Former Pangaea
- Médard Thiry and
- Régine Simon-Coinçon
Published Online: 14 APR 2009
Copyright © 1999 The International Association of Sedimentologists
Palaeoweathering, Palaeosurfaces and Related Continental Deposits
How to Cite
Valeton, I. (1995) Saprolite-Bauxite Facies of Ferralitic Duricrusts on Palaeosurfaces of Former Pangaea, in Palaeoweathering, Palaeosurfaces and Related Continental Deposits (eds M. Thiry and R. Simon-Coinçon), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304190.ch6
- Published Online: 14 APR 2009
- Published Print: 26 MAY 1995
Print ISBN: 9780632053117
Online ISBN: 9781444304190
- laterite-derived facies (LDF);
- saprolitic high-Al clays, high-quality kaolinites and smectites, important by-economic products;
- Guyana Shield in South America, representing succession of planation plains;
- bauxite belt, covering Deccan Peninsula and the Kathiawar block;
- Pangaea-derived land masses;
- kaolinite and halloysite, Al silicates;
- post-bauxitic pedogenic overprinting, revealing polyphase and polygenetic history
The tectonic and morphogenetic evolution of Pangaea with special respect to the late Mesozoic to early Tertiary history of the landscape and the early Tertiary weathering cover are described. Within the ferralitic duricrust of this time span a saprolite–bauxite facies pattern on hilly landscapes and on downwarping platforms is developed in extended newly formed coastal areas after the break-up of Pangaea. The early to middle Eocene was still a time of world-wide flat relief, of world-wide warm current systems in the oceans and therefore of a humid warm climate. The relief of the pre-, syn- and post-bauxitic landscapes indicates tectonic lability and short times for bauxite formation. The facies distribution of the vertically and laterally well-developed saprolite–bauxite facies pattern depends on parent-rock variables, morphology and drainage patterns.
The mineralogy and chemistry of saprolite–bauxite and the quality pattern in bauxite deposits are discussed with respect to the supergene processes. In contrast to ‘normal’ laterites, a strict separation of Al and Si by an effective extraction of silica has prevented the formation of Al silicates in parts of the Box horizon, leading mainly to neomineralization of gibbsite, boehmite and diaspore.
Post-bauxitic tectonic activities have transformed the very flat near-sea-level landscape by subsidence or uplift. Changes of relief and of climate since the Eocene have led to a differentiation of soils dependent on altitude and on climatic zones. Results are either truncated ferralitic profiles and erosional landforms or polygenetic overprinting of saprolites and bauxites by younger soils, forming a complex ‘solum’. Aluminization by ferralitic weathering destroyed the main geochemical parent-rock characteristics, resulting in supergene geochemical environments dominated mainly by Al, Zr, Ti, Ga and Fe, but still marked by some trace element associations indicative of the original parent-rock composition. These specific supergene geochemical domains in the ferralitic duricrusts are very useful as lithostratigraphical marker horizons in terrestrial environments.