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Book Chapter

Onlap stratal architectures in the Grès d'Annot: geometric models and controlling factors

By
Ru Smith
Ru Smith
1
A/S Norske Shell
P.O. Box 40, 4098 Tananger, Norway
Ru.Smith@shell.com
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;
Philippe Joseph
Philippe Joseph
2
Institut Français du Pétrole, 228-232 avenue Napoléon Bonaparte
228-232 avenue Napoléon Bonaparte, 92852 Rueil Malmaison Cedex, France
Philippe.Joseph@ifp.fr
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Published:
January 01, 2004

Abstract

Onlap terminations of deep-marine sandstones in the Grès d'Annot, SE France, exhibit a range of styles, from abrupt onlap to feathering ‘aggradational onlap’ geometries. These are well exhibited in the large exposure of southward onlap terminations at Montagne de Chalufy, on the southern end of the Trois Evêchés Massif (Alpes de Haute Provence). These stratal architectures are here simulated by geometrical models that are governed simply by bounding slope gradients and the ratio of coeval slope to basinal aggradation rates. In cases of no coeval deposition on bounding slopes, pure onlap results. In cases of high slope aggradation rates relative to basinal aggradation rates, a feathered geometry results with successive sandstone beds onlapping against successively younger slope drapes. The cyclicity of alternating sand-rich and sand-poor packets seen at Chalufy results in a stepped climbing trajectory of successive slope base positions, with climb angle equal to bounding slope angle when mud-poor sandy flows deposited sandstone bodies with abrupt onlap, and climbing more steeply when slope drapes are deposited. An implication of this result is that any zones of facies change and palaeocurrent swing that are related to distance from bounding slope will exhibit a comparable vertical trajectory through time. The two end member termination types can be compared with the convergent-baselapping and convergent-thinning seismic facies used in the Gulf of Mexico subsurface and elsewhere. The convergent-baselapping seismic facies may include both abrupt onlap and intervals of feathering aggradational onlap if the presence of slope drapes is not resolvable by the frequency content of the available seismic data.

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Geological Society, London, Special Publications

Deep-Water Sedimentation in the Alpine Basin of SE France: New perspectives on the Grès d'Annot and related systems

P. Joseph
P. Joseph
Institut Français du Pétrole, France
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S. A. Lomas
S. A. Lomas
Baker Atlas Geoscience, UK
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Geological Society of London
Volume
221
ISBN electronic:
9781862394698
Publication date:
January 01, 2004

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