Online Journal for E&P Geoscientists

Abbas, Tarig A.^*1; Bertotti, Giovanni ²
(1) exploration, Petrodar Operating Co., Khartoum, Sudan. (2) Department of Geotechnology, TU Delft, Delft, Netherlands.

Melut basin represents a major rift system in NE African, The basin is a ~250km long and 40-100km wide basin elongated in NW-SE direction located in SE Sudan. Tectonically the basin developed from Early Cretaceous to Miocene times as essentially extensional basin and was then (slightly) reactivated within a transpressional deformation field.

The Melut basin comprises a set of half graben and asymmetrical full graben structures that evolved through reactivation of basement structures during Cretaceous and Tertiary time. The development of the basin is controlled largely by NW-SE trending sub-planar normal master faults although listric faults do exist. Continental clastic constitutes the basin infill which deposited mainly in fluvial, deltaic and lacustrine environments. Stratal geometry and facies patterns suggest that lacustrine sedimentation was coeval with extension as it characterized by wedge shape geometry which fans out towards the major fault. Coarser clastics ascribe mainly to post rift sedimentation as they posses slightly diverge and conformable internal reflector geometry.

The basin has been used as example to relate the amount of horizontal tectonic extension and vertical subsidence during different phases of the basin development. For this purpose structural restoration and cross section balancing coupled with backstripping technique were performed. The result of restored sections indicates that the basin extension is mainly control by basin bounded faults, which reactivated during successive rifting events. Backstripping technique is used to model the tectonic subsidence form well data, the tectonic subsidence curves exhibit three main subsidence events. The early phase took place during the early Cretaceous and terminated by prologue period of poorly constrained erosional event. The second and the third rifting events took place during Late Cretaceous and Mid Tertiary respectively. Both techniques reveal that two third of the estimated extension value took place during Cretaceous time. Moreover the major subsidence events which constrained from the well data are synchronized with pronouns phase of horizontal extension as denoted by the restoration result and this signify that the recorded amount subsidence in the Melut basin is related to crustal stretching and thinning.