The Role of Strike-Slip Faulting on Deep ‘Basement’ Faults in Cretaceous DepositionalHistory and Fiqa Channel Location, as Determined From Analysis of 3D Seismic Over anOffshore Field, Abu Dhabi

摘要

From structural analysis of 3D seismic data over a giant field,rnoffshore Abu Dhabi, a complex pattern of intersecting, broadlyrnconjugate, strike-slip dominated en-echelon fault systems arernobserved from ‘basement’ levels up to latest Cretaceousrnhorizons. Over geologic time these fault systems exertedrnfundamental controls on depositional patterns within the studyrnarea. Use of new attribute techniques, isochron mapping,rnflattening on key intra-Cretaceous horizons, cinematic timeslicern‘movies’ and a review of the available vertical seismicrnsections has indicated that many apparent velocity anomalyrnzones are controlled by deep-seated fault systems developed asrnstrike-slip dominated ‘flower structures’. Spatial continuity ofrnthese fault zones, the most prominent of which trend ~NE-SW,rnexhibit a linear nature on a scale of several kilometers to tensrnof kilometers; have flower-zone geometry in cross-section butrnwith increasingly en-echelon nature at Upper Cretaceousrnlevels; low apparent normal offsets on long fault segments;rnanastomosing, convergent and divergent, patterns at differentrnstratigraphic levels; wrench offset with respect to other deeprnfault systems; throw terminations with rapidly decreasingrndisplacement gradients along en-echelon zones into the crossoverrnzones with other fault systems. There are four prominentrnfault systems that exert control on the depositional systems:rn(1) NE to NNE trending ‘Fiqa’ direction, also delineating localrndepositional highs/lows and Mishrif ‘reef’ margin; (2) NW-SErnzones defining depositional areas of step-wisernthickening/thinning; (3) Conjugate WNW-ESE and WSWENErnen-echelon strike-slip zones, and (4) NNW-SSE faultrnzones displaying local control on thinning or thickening.rnTemporal fault activity on these zones is linked to sedimentaryrnthickening and thinning patterns, though deeper level faultsrnprovided only ‘soft’ links to the sedimentary sequences ofrnearly Cretaceous age. By late Cretaceous times therntranstensional / transpressional fault systems provided ‘hard’rnlinks to the depositional systems (e.g. Fiqa channel system).