KARST-METEORIC DEDOLOMITIZATION IN JURASSIC CARBONATES, LEBANON
Katholieke Universiteit Leuven, Afd. Fysico-chemische Geologie, Celestijnenlaan 200C, B-3001 Heverlee, Belgium, and Lebanese National Council for Scientific Research scholar.
Katholieke Universiteit Leuven, Afd. Fysico-chemische Geologie, Celestijnenlaan 200C, B-3001 Heverlee, Belgium
Katholieke Universiteit Leuven, Afd. Fysico-chemische Geologie, Celestijnenlaan 200C, B-3001 Heverlee, Belgium
Abstract
ABSTRACT. This study shows that dedolomites may indicate emergence and karst meteoric diagenesis, providing invaluable information about the original dolomite rock and the calcitizing fluids. The relative increase of permeability in dolomitized zones (called 'pockets' ) within the limestone rock-mass of the Lebanese Jurassic Kesrouane Formation is believed to have played an important role in enhancing dedolomitization through preferential circulation of karst-meteoric waters in these pockets. Nonstoichiometry of the original dolomites (expressed by mole % CaCO,) appears to be a major driving factor for dedolomitization, while clay content seems to protect the nonstoichiometric dolomites from becoming dedolomites. The calcitizing fluids were fresh oxidizing waters circulating in an open system - typical of karst aquifers. During dedolomitization, Sr, Fe and Mn were released from the pre-existing dolomite minerals without being incorporated in the precipitating calcite. The ∂13C values of the dedolomites supports meteoric diagenesis with contribution of soil derived carbon (values ranging from -2.40 to -2.32 %c PDB), while the 'meteoric calcite line' provides a clue to estimate the ∂I8O value of the dedolomitizing fluid.