DIRECT DATING OF CALCRETIZATION AND MICROBIAL DIAGENETIC EVENTS IN THE UPPER CRETACEOUS BEKHME FORMATION, KURDISTAN REGION OF IRAQ, BY THE U-PB SMALL SCALE ISOCHRON METHOD

Direct dating of calcretes using the recently developed U-Pb small scale isochron (U-Pb SSI) method has led to a better understanding of the relationship between ancient sea level fluctuations, microbial diagenesis and the alteration of marine dolomite, such as the Upper Cretaceous Bekhme Formation in Iraqi Kurdistan. Two major calcretization events have been documented in the Bekhme Formation, using the U-Pb SSI method. The first event, which produced a typical alveolar texture in the calcrete level, occurred at 75.1 ± 1.1 Ma (MSWD= 3.5), coeval with the Campanian age of the Bekhme Formation. The second event occurred 3.8 Ma, and is characterized by pisolitic and laminar crusts that altered the former saddle dolomite inside the geode structures of the Bekhme Formation.

Laser ablation U-Pb geochronology (U-Pb SSI) of calcrete events within the Bekhme Formation, in combination with fieldwork, classical petrography, stable isotopes, REE, and microthermometry evidence, suggest that this pronounced events reflects influences of slip-faults during Late Cretaceous and Pliocene periods. These slip-faults, which detached to basement blocks along deep-seated faults, were indirectly related to Zagros Orogeny Movement.