Clays and Clay Minerals

, Volume 58, Issue 3, pp 388–398 | Cite as

Illitization of Early Paleozoic K-Bentonites in the Baltic Basin: Decoupling of Burial- and Fluid-Driven Processes

  • Peeter SomelarEmail author
  • Kalle Kirsimäe
  • Rutt Hints
  • Juho Kirs


The mineralogical characteristics of Ordovician and Silurian K-bentonites in the Baltic Basin were investigated in order to understand better the diagenetic development of these sediments and to link illitization with the tectonothermal evolution of the Basin. The driving mechanisms of illitization in the Baltic Basin are still not fully understood. The organic material thermal alteration indices are in conflict with the illite content in mixed-layer minerals. The clay fraction of the bentonites is mainly characterized by mixed-layered illite-smectite and kaolinite except in the Upper Ordovician Katian K-bentonites where mixed-layer chlorite-smectite (corrensite) occurs. The variation in expandability plus other geological data suggest that the illitization of Ordovician and Silurian K-bentonites in the Baltic Basin was controlled by a combination of burial and fluid driven processes. The illitization in the south and southwest sectors of the basin was effected mainly by burial processes. The influence of the burial process decreases with decreasing maximum burial towards the central part of the basin. The advanced illitization of the shallowburied succession in the north and northwest sectors of the basin was enhanced by the prolonged flushing of K-rich fluids in relation to the latest phase of development of the Scandinavian Caledonides ≈420–400 Ma.

Key Words

Baltic Basin Illite-smectite Illitization K-bentonite 


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Copyright information

© The Clay Minerals Society 2010

Authors and Affiliations

  • Peeter Somelar
    • 1
    Email author
  • Kalle Kirsimäe
    • 1
  • Rutt Hints
    • 1
    • 2
  • Juho Kirs
    • 1
  1. 1.Department of GeologyUniversity of TartuTartuEstonia
  2. 2.Estonian Museum of Natural HistoryTallinnEstonia

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