Mechanisms of Complete Dolomitization in a Carbonate Shelf: Comparison between the Norian Dolomia Principale (Italy) and the Holocene of Abu Dhabi Sabkha

  1. Bruce Purser,
  2. Maurice Tucker and
  3. Donald Zenger
  1. S. Frisia

Published Online: 14 APR 2009

DOI: 10.1002/9781444304077.ch5

Dolomites: A Volume in Honour of Dolomieu

Dolomites: A Volume in Honour of Dolomieu

How to Cite

Frisia, S. (1994) Mechanisms of Complete Dolomitization in a Carbonate Shelf: Comparison between the Norian Dolomia Principale (Italy) and the Holocene of Abu Dhabi Sabkha, 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.ch5

Author Information

  1. Università degli Studi di Milano, Dipartimento di Scienze della Terra, via Mangiagalli 34, I-20133 Milano, Italy

Publication History

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

ISBN Information

Print ISBN: 9780632037872

Online ISBN: 9781444304077

SEARCH

Keywords:

  • complete dolomitization mechanism in carbonate shelf - Norian Dolomia Principale (Italy) and Holocene of Abu Dhabi Sabkha;
  • massive dolomite formation in carbonate platforms;
  • transmission electron microscopic (TEM) observations and geochemistry;
  • Norian Dolomia Principale – dolomitized sediments deposited on great tidal flat of Pangean Gulf;
  • five different textures of dolomite - in Dolomia Principale subtidal and peritidal facies;
  • stable isotope analysis;
  • Type 1 and Type 2 dolomites;
  • Abu Dhabi sabkha dolomites;
  • proposed mechanisms of dolomitization

Summary

The diagenetic history of the Late Triassic Dolomia Principale tidal-flat complex is reconstructed utilizing transmission and analytical electron microscopic techniques and comparison with modern Abu Dhabi dolomite analogues. The Dolomia Principale, which completely dolomitized peritidal and subtidal cycles, shows five dolomite texture types with different stable isotope values. The early products of shallow subsurface dolomitization are preserved, and are calcian and characterized by fine, pervasive modulated microstructures. Texturally, microstructurally and geochemically similar dolomites are observed in subtidal facies of Abu Dhabi, generally replacing aragonites and Mg-calcites. The subsequent dolomitization history of the Dolomia Principale continues with the precipitation of progressively more ideal dolomites, with coarse modulated microstructures or ribbon structures. Ideal dolomites, generally characterizing void-filling crystals or the outer part of matrix-replacive as well as mimetic dolomites, show only a few dislocations. Dislocation networks characterize the highest-temperature dolomites. A considerable spread of δ18O values (+3.3‰ to below –4‰) characterizes ‘matrix’ dolomite crystals with different chemical compositions and microstructures coexisting in the same crystal. This spread is considered to be the result of an admixture of signals coming from calcian dolomites and ideal ones precipitated later in the diagenetic history. Calcian dolomites, slightly Ca dolomite, some ideal dolomite ‘overgrowths’ and void fillings with positive δ18O still form during the same cycle. δ18O-depleted ideal dolomites formed during burial. The dolomitizing fluids were provided by the cyclic subaerial exposures to which the Dolomia Principale was subjected, allowing saline fluid circulation through pores and fractures.