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Geological Society, London, Special Publications; 2000; v. 172; p. 177-191;
DOI: 10.1144/GSL.SP.2000.172.01.09
© 2000 Geological Society of London

Cenozoic

Tectonically enhanced forced regressions: examples from growth folds in extensional and compressional settings, the Miocene of the Suez rift and the Eocene of the Pyrenees

Robert L. Gawthorpe1, Matt Hall1,2, Ian Sharp1,3 & Tom Dreyer3

1 Basin & Stratigraphic Studies Group, Department of Earth Sciences, University of Manchester, Manchester M13 9PL, UK Rob.Gawthorpe{at}man.ac.uk
2 Statoil, Exploration & Production Division, N-4035 Stavanger, Norway
3 Norsk Hydro Research Centre, Sandsliveien 90, N-5020 Bergen, Norway

This paper examines the stratal geometries and facies stacking patterns associated with forced regressions around fault-propagation folds in extensional and compressional settings. Case studies are documented from: (i) the Miocene of the Suez rift and (ii) the Eocene of the Ainsa piggyback basin, Pyrenees. Despite the different tectonic settings, the stratal geometries and facies stacking patterns are remarkably similar. Distinctive sharp-based shoreface sandstones, formed as a result of forced regression, were deposited around growth anticlines. The forced regressive shoreface sandstones ‘shale-out’ rapidly basinward away from the growth anticlines and sit abruptly within offshore mudstones of highstand (HST) and transgressive (TST) systems tracts along the flanks of the growth anticlines.

As fold amplification proceeded, older sandbodies were rotated to dip more steeply, and there is commonly a 2–5° angular difference between successive forced regressive sandbodies. This progressive tilting, coupled with marine erosion during relative sea-level fall has completely removed HST and TST deposits near anticline crets, and led to vertical amalgamation of individual forced regressive sandbodies. The resulting stratal geometries clearly result from the tectonic enhancement of forced regression.