Burial Dolomitization of Organic-Rich and Organic-Poor Carbonates, Jurassic of Central Tunisia

  1. Bruce Purser,
  2. Maurice Tucker and
  3. Donald Zenger
  1. M. Soussi and
  2. A. M'Rabet

Published Online: 14 APR 2009

DOI: 10.1002/9781444304077.ch24

Dolomites: A Volume in Honour of Dolomieu

Dolomites: A Volume in Honour of Dolomieu

How to Cite

Soussi, M. and M'Rabet, A. (2009) Burial Dolomitization of Organic-Rich and Organic-Poor Carbonates, Jurassic of Central Tunisia, in Dolomites: A Volume in Honour of Dolomieu (eds B. Purser, M. Tucker and D. Zenger), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304077.ch24

Author Information

  1. Université de Tunis II, Faculté des Sciences, Départment de Géologie, Laboratoire de Géologie du Pétrole et Bassins Sédimentaires, Campus Universitaire 1060, Tunis, Tunisia

  1. Université de Sfax, Faculté des Sciences, Département de Géologie, 3038 Sfax, Tunisia

  2. ETAP, 27 bis Avenue Khereddine Pacha, 1002 Tunis, Tunisia

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 25 MAY 1994

ISBN Information

Print ISBN: 9780632037872

Online ISBN: 9781444304077

SEARCH

Keywords:

  • burial dolomitization of organic-rich and organic-poor carbonates, Jurassic of Central Tunisia;
  • Lower Nara dolomites;
  • Jurassic organic-rich burial dolomites;
  • Middle Nara organic-rich dolomites;
  • Upper Nara dolomites;
  • dolomite cements in fractures;
  • organic matter - factors controlling dolomitization in anoxic environments

Summary

Sedimentological, isotopic, geochemical and fluid-inclusion studies of Jurassic organic-rich and organic-poor carbonates from the Nara Formation in Central Tunisia have led to the definition of three groups of dolomites. The Lower Nara dolomites (Liassic) correspond to peritidal and bioclastic deposits; they are depleted in heavy oxygen (δ18O of –7‰ PDB) and impoverished in strontium (30 ppm) and contain fluid inclusions whose temperature of homogenization has reached 120°C. The Middle Nara dolomites (Toarcian) are organic-rich, ferroan and relatively enriched in strontium (110 ppm); they have light oxygen and carbon isotopic signatures (δ18O of –3 to –12‰ PDB and δ13C of –2 to +1.5‰ PDB). δ13C values which negatively correlate with TOC indicate that part of the carbon was derived from organic matter, either during early bacterial reduction of sulphates or later during deep thermal decarboxylation. The Upper Nara dolomites (Malm) correspond to hemipelagic carbonates and are impoverished in 18O (δ18O of –5‰ PDB) and Sr (60 ppm). These Nara dolomites formed in the subsurface, during shallow to deep burial and under increasing temperatures. Dolomitizing fluids seem to have been multiple in origin and include interstitial (connate) seawater, waters expelled from neighbouring shales and updip-flowing basinal marine water. Dolomitization and associated recrystallization started during the Lower Cretaceous, and were completed by the end of the Upper Cretaceous. The massive dolomites have been affected by post-Cretaceous fractures, the latter having been cemented by hydrothermal saddle dolomite. This study confirms that aggradational burial dolomitization by warm and saline waters can be an important process in dolomite genesis, and that organic matter may be an active controlling factor of dolomitization in anoxic environments.