Structural and tectonic evolutions of Sabratah Basin, offshore NW Libya

Reeh, Giuma (2015). Structural and tectonic evolutions of Sabratah Basin, offshore NW Libya. University of Birmingham. Ph.D.

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Abstract

Three volumes of seismic data, together with longer 2D lines, well data and regional gravity and magnetic data, have been used to investigate the structure and formation of the Sabratah Basin, thought to be formed as an extensional basin between the Libyan Coastal fault system and South Graben Fault Zone during the Middle to Late Triassic. The study has investigated the crustal structure, subsidence history and structural evolution of the basin. Tectonic subsidence was calculated by assuming 1D Airy isostatic equilibrium using a total of 20 wells. The result shows two rifting events. Rift event 1 started in Middle Triassic and continued until the end of Triassic (228-200Ma). Rift event 2 started in the Upper Cretaceous no earlier than (100 Ma). The depth to the Moho has been calculated by the methods of Airy- Heiskanen model, Warner (1987), 2D gravity model and deep seismic profiles. The result shows crustal thinning under the Sabratah Basin. The two 3D seismic volumes within the northern part of the Sabratah Basin reveal the presence of en-echelon folds aligned ENE-WSW (N75°) and two grabens trending N150° separating the folds. Three trends of faults were recognised in the study area N150°, N110° and N60°. The seismic interpretation suggests that the folds probably developed by dextral transpressional shear during the Alpine compressional phase between Africa and Europe as right lateral movement. This motion was accompanied with E-W transcurrent fault which probably terminated in a horsetail composed of a fan of normal faults in Bouri block. Diapiric phenomena related to Upper Triassic Lower Jurassic salt affected the western part of the study area. The salt structures have distinct E-W trends. Thus, salt movements appear to be associated with E-W trending strike-slip faults. Movement of Upper Triassic Lower Jurassic salt began in the upper Cretaceous and forms a decollement which acts as glide-plane for series of listric faults separating listric extensional structures above from planar extensional structures below the base Jurassic.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):