Structure of the East Shetland Platform, northern North Sea

The East Shetland Platform formed a regional high throughout the Mesozoic and Tertiary with only a thin Triassic to Recent succession preserved. Seismic data reveal the underlying structure and stratigraphy. Complex seismic reflections are seen within the basement and may indicate basement thrust duplexes and lateral ramps, recording Caledonide deformation. A distinctive change in seismic character, traceable over the entire area, marks the base of a sedimentary package >7.5 km thick which overlies and locally onlaps a regionally persistent top basement reflector. This package is thought to be Devonian. The recognition of several internal discontinuities within it may permit subdivision into tectono-stratigraphic units. Local divergence of the reflectors within the Devonian succession provides evidence of syn-sedimentary growth faulting, perhaps due to extension in the hanging wall of reactivating, rolled back Caledonide thrust faults. The Devonian sequence is locally deformed into symmetrical to eastward-vergent folds, these marking a pre-Mesozoic compressional deformation phase of probable Variscan age. The Devonian strata on the East Shetland Platform may provide local hydrocarbon charge from oil-prone lacustrine source rocks, as well as fluvial sandstones with moderate reservoir potential. Dipping and locally intensely folded Devonian strata can offer a range of structural and stratigraphic traps in this poorly explored area.