Tobelitization of smectite during oil generation in oil-source shales. Application to North Sea illite-tobelite-smectite-vermiculite

Victor A. Drits, Holger Lindgreen, Boris A. Sakharov, Hans Jørgen Jakobsen, Alfred L. Salyn, Lidia G. Dainyak

Research output: Contribution to journalArticleResearchpeer-review

48 Citations (Scopus)


Illite-smectite (I-S) minerals isolated from Upper Jurassic oil-source rock shales from Denmark and the North Sea have been investigated by X-ray diffraction, thermal analysis, infrared, Mössbauer, and solid-state nuclear magnetic resonance spectroscopies and chemical analysis. Detailed structures have been determined in order to reveal the diagenetic transformation mechanism in these shales. Generally, in oil-source rocks of sedimentary basins, oil generation takes place simultaneously with the diagenetic transformation of I-S. We demonstrate a link between the two reactions: NH3 released from kerogen during maximum oil generation is fixed as NH+4 in the NH4-bearing mica or tobelite layers formed from smectite or vermiculite layers in I-S, in a diagenetic interval which we name the 'tobelitization window'. Due to this solid-state transformation, mixed-layer structures have been formed consisting of interstratified illite, tobelite, smectite and vermiculite layers (I-T-S-V) and having maximum ordering of illite + tobelite and smectite layers for R = 1. The tobelitization of smectite in I-S is probably typical for all oil-source rock shales.

Original languageEnglish
Pages (from-to)82-98
Number of pages17
JournalClays and Clay Minerals
Issue number1
Publication statusPublished - Feb 2002


  • Ammonium
  • Diagenesis
  • Illite-smectite
  • Jurassic
  • North sea
  • Oil-source rock
  • Shales

Programme Area

  • Programme Area 3: Energy Resources


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