A geophysical study of the salt tectonics of the Sabratah basin, NW-offshore Libya

Abuhajar, Mohamed Ibrahim (1991) A geophysical study of the salt tectonics of the Sabratah basin, NW-offshore Libya. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Geophysical studies (using the seismic, gravity and magnetic methods) have been carried out with the principal aim to investigate the nature and extent of salt tectonics in the Sabratah Basin, NW-offshore Libya. The Sabratah Basin is located within a large intracratonic basin situated on the passive continental margin of the African plate. Diapiric phenomena related to Triassic salt movement have affected the study area. Sedimentary units in the Basin were deformed as a result of halotectonic and halokinetic movements during Upper Cretaceous time. The seismic reflection investigation and its interpretation shows the extent of diapiric phenomena and salt structure configuration and its influence on sediment sequence development. The study area was divided into three structural domains: the Salt Domain, the Continental Sheld Domain, and the Thick Sediment Domain. The salt structures have been classified into three types: salt walls, salt diapirs, and salt pillows. The Continental Shelf Domain has been affected by extensional faults related to cratonic rifting, and is characterized by considerable subsidence and volcanic activity (intrasedimentary volcanic units). The sediment thickness of the Thick Sediment Domain has been estimated to be greater than 9 km. The dominant tectonic trends in the Basin are: (i) a NW/SE Sirtic tectonic trend. (ii) a W-E Jeffara tectonic trend, and (iii) a W-E Salt tectonic trend. The geological evolution model for the Libyan Continental Shelf Domain has shown the development of this domain, from Late Triassic/Early Jurasic time to the present time. The combination of several geophysical methods, has proved particularly useful in identifying the cause of various anomalies and delineating regional and local structures in the Sabratah Basin. It is clear that uncertainties in interpretation from any one method are reduced by this combined approach. The gravity and magnetic maps exhibit a strong correlation with the regional geological controls and seismic interpretation. These maps support the existence of the salt/thick sedimentary basin and intrasedimentary volcanic units, which can be correlated with the main sources of the negative and positive potential field anomalies, respectively. Basement depth estimation is 6 km in the Continental Shelf Domain, greater than 9 km in the Thick Sediment Domain. No depth estimate was possible in the Salt Domain.