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Abstract: High Resolution Sequence Stratigraphy of a Wave- and Tide-Dominated Deltaic Reservoir System in a Tectonically Active Setting. Example of the Brent Group on Dunbar, Grant and Ellon Fields, North Sea, United Kingdom

Benoit Didier, Remi Eschard, Jean-marc Feroul

The Brent group records a 15-20 million year deltaic regressive-transgressive cycle. The flood plain sediments of the Ness overlies the Etive barrier to foreshore facies, themselves passing to wave-dominated shoreface deposits (Rannoch). This progradation is followed by a transgression which begins during the lower Ness. The flood plain passes laterally and vertically to sandy tidal dominated nearshore complexes, each complex passing seaward to sandy shoreface to form tens of kilometres wide and 10 to 25 m thick flow units, limited at their base by a Flooding Surface and usually capped by very correlatable aggrading coal beds.

On Dunbar field, the former model of transgression is complicated by the presence of active fault scarps: on the hanging wall, the Tarbert shoreface is replaced by an unusual succession: from the base to the top:

-- BASAL SANDS: plurimetric conglomeratic sandstones with garnets placers.

-- MIDDLE SHALE: plurimetric fining-up sandstones grading upward into open marine black shale.

-- UPPER MASSIVE SANDS: hectometric medium to very coarse-grained sandstones.

Erosions occur on footwall (the whole Jurassic can be eroded during Tarbert deposition); the products of these erosion are resedimented on the hanging wall: the Basal Sands being interpreted as a transgressive lag, and the Upper Massive Sands as (highstand?) fan deltas rapidly thinning out to the North and to the East.

In terms of sequence stratigraphy, it means that we have to correlate a sequence boundary on the footwall with transgressive or highstand deposits on the hanging wall.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France