Salt tectonics in the Thumrait area, in the southern part of the South Oman Salt Basin: Implications for mini-basin evolution

Abstract

ABSRACT The Upper Proterozoic - Lower Cambrian South Oman Salt Basin contains exploration targets consisting principally of slabs of carbonate encased within the infra-Cambrian Ara Salt. The southern part of the South Oman Salt Basin was reviewed by using a 40 by 50 km 3-D seismic survey, 30 2-D regional seismic lines and 15 wells. The study focused on the evolution of the Ara Salt in relation to the overlying lower Paleozoic Nimr, Mahatta Humaid and Ghudun groups. Deformation of the thick sequence of Ara Salt dominated the history of mini-basins or “Haima pods” that developed above the salt. The syn-kinematic, predominantly clastic units of the Nimr and overlying Mahatta Humaid groups were deposited in the mini-basins above the Ara Salt. These sequences vary greatly in thickness due to salt movement. In seismic cross-sections, the Ara Salt is opaque, and obscured by seismic multiples generated by sub-horizontal reflectors higher in the section. Where internal geometries are imaged, however, complex internal structures are commonly observed. The Ara Salt structures evolved through several stages of deformation that were driven mainly by phases of sediment progradation from the west and northwest. Four main evolutionary phases for the mini-basins have been identified. Pre-existing topography and regional faults also played a role in triggering and delineating the regional salt trends. The basin has retained much the same shape from the Devonian Period until today. In contrast, in northern Oman, six salt domes have pierced the surface due to the reactivation of major basement faults during the late Palaeozoic.