Tectonic Evolution of the Sedimentary Basins of Abu Dhabi

Abstract

The sedimentary basins of Abu Dhabi, United Arab Emirates, have resulted from over 600 Myr of unique geodynamic settings disclosing cratonic lithospheric stretching, passive margin formation, and lithospheric deflection in active settings. Yet, the tectonic evolution of the area remains puzzling due to the lack of resolving data and the presence of a ~15-km-thick stratigraphic record overlying the basement that has not been sampled by drilling nor seismic imaging. Lithological, biostratigraphical, and geophysical information from 549 explorational wells amended by interpretation of 363 2D seismic reflection profiles and 7 seismic 3D volumes were integrated to decipher the tectonostratigraphic evolution, subsidence and uplift history and isostatic flexure and lithospheric structure. Seismic and well-stratigraphic analysis suggests seven seismic sequences bounded by plate-wide unconformities associated with the tectonic evolution of the Arabian Plate. These seismic sequences are linked to three dominant tectonostratigraphic mega-sequences: pre-Permian intra-cratonic, Permian-Turonian passive margin, and Coniacian-Pleistocene active margin mega-sequences. The tectonic 1D subsidence analysis indicates two episodes of rifting: the oldest rift was initiated at 272 Ma and lasted for ca. 20 Myr, and the final rifting event occurred at 160 Ma and lasted for ca. 25 Myr, which are linked to the initial Tethys opening and the final Gondwanaland fragmentation. Moreover, compressional phases were identified during the Late Cretaceous and in the Oligocene-Miocene, coinciding with the emplacement of the Semail ophiolite and the collision of the Arabian-Eurasian plates, both causing additional subsidence and flank uplift, forming the Aruma foreland basin in the east and the Pabdeh foreland basin in the east and north. A uniform depth extension model implies that the lithosphere was stretched with factors between 1.13- 1.33 and 1.11-1.34 during the initial and final Gondwana fragmentation. The 3D flexural backstripping modeling suggested that different loading histories have produced anomalous flexural responses in the contiguous lithosphere, especially during the post-Cretaceous and post-Oligocene time. Basement flexurally restored maps indicate two key structuring periods: one influenced by pre-existing structures in the Neo-Proterozoic responding to N-trending extensional events, and the other associated with Semail ophiolite emplacement in the early Upper Cretaceous, marking the transition from post-rift isostatic flexure to flexure under mass loading. Contrary to the consensus of substantial subsidence to post-ophiolite emplacement and foreland basin formation, the 3D flexural modeling results indicate that the primary subsidence, accommodation creation, and sediment deposition occurred during the Neo-Proterozoic to Permian period. The lithosphere cooled during the Triassic and Jurassic periods, driven by thermal-induced post-rift processes associated with initial and final Gondwana fragmentation. The lithospheric modeling with a semi-finite plate suggests an effective elastic thickness, Te, of 25 km produces a flexure similar to that resulting from the emplacement of the Semail ophiolite on the Arabian Plate's northeastern rifted margin.

Date of Award	20 May 2024
Original language	American English
Supervisor	Mohammed Ali (Supervisor)