Authigenic Clay Minerals in Continental Evaporitic Environments

  1. Médard Thiry and
  2. Régine Simon-Coinçon
  1. J. P. Calvo1,
  2. M. M. Blanc-Valleron2,
  3. J. P. Rodríguez-Arandía1,
  4. J. M. Rouchy2 and
  5. M. E. Sanz1

Published Online: 14 APR 2009

DOI: 10.1002/9781444304190.ch5

Palaeoweathering, Palaeosurfaces and Related Continental Deposits

Palaeoweathering, Palaeosurfaces and Related Continental Deposits

How to Cite

Calvo, J. P., Blanc-Valleron, M. M., Rodríguez-Arandía, J. P., Rouchy, J. M. and Sanz, M. E. (1995) Authigenic Clay Minerals in Continental Evaporitic Environments, in Palaeoweathering, Palaeosurfaces and Related Continental Deposits (eds M. Thiry and R. Simon-Coinçon), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304190.ch5

Author Information

  1. 1

    Departamento de Petrología y Geoquímica, Facultad Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain

  2. 2

    Laboratoire de Géologie, Muséum National d'Histoire Naturelle, 43 rue Buffon, 75005 Paris, France

Publication History

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

ISBN Information

Print ISBN: 9780632053117

Online ISBN: 9781444304190

SEARCH

Keywords:

  • Marinesian deposits, consisting of clayey lenses;
  • salt flocculation;
  • Palygorskite, precipitating from pore-waters;
  • clay mineral assemblage, comprising Al–Mg smectites;
  • Marinesian, fibrous clay minerals forming in interdunes;
  • palaeosols, consisting indurated sediments;
  • Miocene formations of Madrid Basin, containing clay minerals

Summary

A variety of clay minerals are commonly found in modern continental saline environments and clays also form a considerable portion of the sedimentary successions accumulated under evaporitic conditions in continental settings of the past. Research conducted world-wide for more than three decades indicates that specific clay assemblages form by authigenesis in such arid to semi-arid environments. Clay authigenesis, whether through direct precipitation from solution (neoformation) or by transformation of precursor minerals, mainly pyroclastics and detrital clays, takes place both in soil profiles and in various saline lake subenvironments. Examples of cation exchanges leading to authigenic clay minerals have been reported from many modern lakes and soils of North and South America, Africa and Australia. In most cases, significant removal of Mg+2, enhanced by reaction with silica from the lake waters, results in the formation of magnesium silicates. Magnesium-smectites (stevensite, saponite, hectorite), kerolite and sepiolite have been determined as rather common authigenically formed minerals. In addition to these occurrences, palygorskite, either associated with sepiolite or as the predominant clay mineral, is present in many soils of arid to semi-arid regions. Minor occurrence of other clay minerals, e.g. corrensite, nontronite, Li- and Al–Mg-rich clays together with a variety of mixed-layer minerals, has also been reported from both modern and ancient continental saline settings. Illitization of precursor clay minerals is also thought to be a significant process of clay authigenesis in these environments.

A review of clay occurrences from Tertiary evaporite successions in France, Spain, western USA, and Pleistocene formations of east Africa provides evidence that the aforementioned clay mineral assemblages, especially those dominated by Mg-rich clays, are also typical in sediments accumulated in ancient continental evaporitic settings. The comparison between basins developed in active tectonic systems, for instance the grabens related to the western European Rift System during the Paleogene, and basins evolving under relatively quiescent conditions, shows that in the latter case the formation of authigenic clays was favoured because of the lower sedimentation rates in the basins. There is usually a greater abundance of authigenic clays in lakemargin environments owing to large variations in salinity, pH and pCO2, which can induce their formation. The sensitivity of clays to salinity fluctuations in the lake waters makes the stratigraphical progression of the clay mineralogies a useful indicator of lakelevel fluctuation, probably related to climatic changes, in continental evaporitic settings.