EVOLUTION AND ARCHITECTURE OF BLUE NILE BASIN USING INTEGRATED GRAVITY, SEISMIC AND WIRE LINE LOGS

Abstract

ABSTRACT Parts of the Blue Nile basin showed good oil indications, the puzzling question is why no oil draining. The common geological sense will go towards the lateral lithologic variations and its impacts on the porosity and permeability. So the attention gone towards the dynamics of the processes that governs and generate this architecture and the modes of its development. By decompaction stratigraphic seismic sections, isostasy, recover the geometry of the crust at time of rift, calculating and adding the contribution of sediments and water to rift gravity anomaly, compare between the observed free air and the calculated gravity. Applying Process Oriented Gravity Modelling technique (POGM), results a good discrimination of gravity contributions of sediments and rift, and a value of 45 km thickness of elastic lithosphere, this value used to constrain the backstripping technique. Results from the backstripping shows the basin is a half graben type, the extension factor varies from 1.04 up to 1.1. This extension is accommodated by listric normal fault and the rotated blocks which compromise the hanging wall and developed to be the basin. The relative movement between these blocks and the foot wall goes different behaviors from acting independently to act as one unit this interplay change the normal faults into reverse faults, made temporal segmentation of the basin, relief, internal drainage patterns and migration of basin depocentre. From tectonostratigraphic point of view, the evolution of this basin that produces the present architecture is given by different paleoenviroments varied from ephermal lakes, lacostrine, fluvial, and alluvial. Their positions in terms of time and space are controlled by interplay of the sediment supply and the basin capacity which are climatic and structural/thermal subsidence dependants respectively. Tracking of a spatial and temporal facies changes could be quantified using subsidence recovered by 1D inverse method determining lithospheric strain rate variation at different times which can be correlated with information from the boreholes.