Lateritization, Geomorphology and Geodynamics of a Passive Continental Margin: The Konkan and Kanara Coastal Lowlands of Western Peninsular India

  1. Médard Thiry and
  2. Régine Simon-Coinçon
  1. M. Widdowson1 and
  2. Y. Gunnell2

Published Online: 14 APR 2009

DOI: 10.1002/9781444304190.ch10

Palaeoweathering, Palaeosurfaces and Related Continental Deposits

Palaeoweathering, Palaeosurfaces and Related Continental Deposits

How to Cite

Widdowson, M. and Gunnell, Y. (1995) Lateritization, Geomorphology and Geodynamics of a Passive Continental Margin: The Konkan and Kanara Coastal Lowlands of Western Peninsular India, in Palaeoweathering, Palaeosurfaces and Related Continental Deposits (eds M. Thiry and R. Simon-Coinçon), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304190.ch10

Author Information

  1. 1

    Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK76AA, UK

  2. 2

    Laboratoire de Géographie Physique, CNRS-UPRES-A 6042, Université Paris 7, case 7001, 2 Place Jussieu, 75251 Paris Cedex 05, France

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 26 MAY 1995

ISBN Information

Print ISBN: 9780632053117

Online ISBN: 9781444304190

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Keywords:

  • geology and landscape of the western Indian margin;
  • continental flood basalts (CFB), Deccan Traps;
  • magmatic underplating and denudational isostasy;
  • Palghat-Cauvery shear zone;
  • Western Ghats, dividing peninsular India;
  • laterite, common in western peninsular India;
  • laterites, developing in Konkan and Kanara regions

Summary

The existence of extensive belts of lateritization along the coastal lowlands of tropical continental margins is a well-documented phenomenon and this research presents a detailed study of the western coast of peninsular India (12°–18°N). The western coast of India is a passive continental margin and its coastal low-lands evolved geomorphologically during middle to late Tertiary times. The associated extensive laterites testify to an important and widespread lateritization that affected western India during this time. These laterites developed upon a pedimented surface resulting from the recession of the Western Ghats escarpment when climatic and tectonic conditions favourable to deep weathering reached an acme; at least two generations of laterite formations may be recognized. The most extensive phase of lateritization was consequent to the development of the pedimented surface, because this provided an ideal topographical site for protracted deep weathering. Importantly, this pediment surface has been cut into two distinct lithological terranes, which differ fundamentally in both their geological age and structure. To the north, the laterite is developed upon the Deccan basalts of Late Cretaceous to early Tertiary age (c. 65–67 Ma) which have provided a laterite protolith of remarkably restricted and predictable composition. South of 16°30′, the coastal laterites have evolved upon the heterogeneous pre-Deccan basement, which comprises high-grade (i.e. Peninsular gneisses) and low-grade sedimentary lithologies of Archaean-Proterozoic age (i.e. Dharwar metasediments), and irregular shaped granitic intrusions of Early Proterozoic age.

The objectives of the current work are threefold: first, to explore similarities of laterite development across these different geological terranes, thereby demonstrating the ubiquity of both lateritization and controlling geomorphological processes. Such ubiquity clearly points to a fundamental morphotectonic control during evolution of the margin. Second, to outline the chemical and physical differences of laterite types across the Konkan-Kanara lowlands, which inevitably exist as a result of fundamental differences in the underlying geology. Thirdly, the morphology of the lateritized pediment surface is investigated with respect to the morphotectonic development of the Indian margin. The elevated position of the Indian coastal laterite belt (c. 60–200m), together with associated development of an entrenched drainage confirms its geological antiquity, and indicates that widespread and permanent uplift has affected the margin during late Tertiary times. Moreover, cambering of this lateritized coastal palaeosurface is consistent with current models advocating seaward flexuring of rifted continental margins in response to onshore denudational unloading and concomitant offshore sedimentary loading.