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ABSTRACT: Influences on sedimentation in active extensional basins

Oliveira, L.O.A.1, K. McClay2, D. Waltham2, G. Nichols2
(1) Petrobras S.A./E&P/GEREX, Rio de Janeiro, RJ, Brazil
(2) Royal Holloway University of London, Egham, Surrey, United Kingdom

This paper analyzes the interaction between segmented, extensional fault systems and rift basin sedimentation. The aim is to understand the role played by controlling factors responsible for the syn-rift development of transverse, footwall-derived fan systems. These are common deposits present in half-grabens and closely related to the formation of oil and gas fields. These sedimentary bodies develop in the hanging wall of main fault segments at the transition zone from subaerial to marine environments and are, therefore, at a location that records the effects of tectonic, sedimentary, isostatic and eustatic processes.

An integrated, three-dimensional, numerical model was used to evaluate individual influences upon the stratigraphy. Effects associated with temporally and spatially variable rates of local subsidence and sediment supply as well as low and high frequency fluctuations in base level were investigated at a reservoir-scale.

Coarse-grained fans well exposed in the central, eastern margin of the Gulf of Suez provided real data to constrain the simulations and were used in comparisons with model outputs. Results indicate that widespread erosional unconformities are not to be expected within syn-rift successions; rift margin uplift does not appear to trigger progradation of marginal deposits; small-scale sequences are likely to be related to varying rates of coarse sediment supply and glacio-eustatic variations in sea level do not seem to have occurred in the Miocene of the Gulf of Suez.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia