U-Pb Direct Dating of Multiple Diagenetic Events in the Upper Cretaceous Carbonate Reservior of Bekhme Formation, Kurdistan-Ne Iraq

Abstract

This study concerns the fieldwork, optical observation, and the absolute LA ICP-MS U-Pb dating of hydrothermal cementation, particularly in tectonically controlled fractures filling saddle dolomites and blocky calcites in the carbonate succession of Bekhme Formation (Campanian–Maastrichtian) within Zagros Folded Zone in NE-Iraq. Direct dating using the recently developed U-Pb IC-PMS on the Upper Cretaceous reservoir carbonates led to a better understanding of the relationship between ancient sea level fluctuations, microbial diagenesis and the alteration of marine dolomites in the formation. Two major near surface diagenetic events are documented using the laser ablation LA U-Pb 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 of the calcrete events within the Bekhme Formation, in combination with fieldwork, classical petrography, and stable isotopes, suggest that these pronounced events reflect influences of slip-faults during the Late Cretaceous and Pliocene periods. These slipfaults, which detached basement blocks along deep-seated faults, were indirectly related to Zagros Orogeny Movement. In conclusion, a tectonic model is developed for Harir-Safin anticlines that combines fieldwork observations, petrography, geochemistry, and U-Pb numerical age data. The latter method brings new insight into the dating of the fractures/geodes formation and the generation of the HT fluids controlled by tectonics.

AAPG Datapages/Search and Discovery Article #90370 ©2020 AAPG Middle East Region Geoscience Technology Workshop, 3rd Edition Carbonate Reservoirs of the Middle East, Abu Dhabi, UAE, January 28-29, 2020