Characteristics, genesis and parameters controlling the development of Cretaceous-Tertiary hydrothermal dolomitization (SE-France and NE Iraq) associated with a newly discovered calcretization phase (NE Iraq): timing of the sedimentary and diagenetic events

Triassic-Jurassic outcrops in Provençal Domain-SE France and Upper Cretaceous Bekhme Formation in Harir-Safin anticlines-NE Iraq are extensively fractured and dolomitized along open spaces in carbonate rocks. Extensive fieldwork, enhanced petrography and geochemistry (trace, REE, major elements, 87Sr/86Sr, δ18OVPDB, δ13CVPDB), and U-Pb datings demonstrate the multi-phase generation of saddle dolomites and blocky calcites formed by the action of deep hot brine fluids, which migrated along fault zones.Petrography and geochemistry revealed three main diagenetic stages in the French Triassic (T)-Jurassic (J) studied outcrops. The first stage is characterized by crystalline replacive dolomites (D1T/ DJ) and medium-sized dolospars (D2T) precipitated in the eogenetic realm from normal seawater and meteoric fluids. The second stage with medium- to coarse-grained saddle dolomites (SD1T/J and SD2T/J) formed under shallow diagenetic realm during Early Cretaceous times, and very coarse-sized zoned and unzoned saddle dolomites (SD3T/J, SD4T/J, and SD5J, SD6J, DrJ) precipitated under deep diagenetic realm (Th between 120 °C and 278 °C) during a Late Cretaceous tectonic activity. Two types of stylolites, extensive fracturing of the carbonates, and breccia/zebra structures, were also formed as a result of the activities of two recognized sub-generations of hydrothermal fluid influxes associated to the second stages. Therefore, they are characterized by a pervasive polyphasic hydrothermal dolomitization that occurred along fractured zones with a wide range of δ18OVPDB and 87Sr/86Sr values. The transition from high (Th between 81 °C and 278 °C; av. = 207 °C) to low (Th between 44 °C and 77 °C; av. = 61 °C) fluid temperatures identifies the third stage of diagenesis. This stage produced the late calcitic cements C1T and C1J with extra-negative oxygen and carbon isotope compositions, and this is related to two different fluids during the uplifting of the studied area in Late Cretaceous
Doctorat en Sciences
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