Abstract: Experimental Deformation of Prograding Sedimentary Wedges Above a Viscous Source Layer

B. C. Vendeville, H. Ge, M. P. A. Jackson

We used experimental models to investigate the deformation of a brittle sediment wedge (modeled by sand) prograding above a salt or shale layer (modeled by viscous silicone). Models initially comprised two horizontal, tabular layers: a viscous source layer overlain by an overburden sand layer. We episodically deposited thick sand wedges thinning out seaward on top of the tabular layers. Deformation was driven solely by gravity instability caused by the surface slope of the wedge. Deformation varied between two end members: seaward expulsion of the source layer and seaward spreading of the brittle wedge.

"Salt" was expelled seaward when the source layer was thick, the overburden was denser than the source layer, or the regional overburden layer was thick. The thick, landward part of the wedge subsided and expelled the underlying source layer, partly as allochthonous "salt" extrusions analogous to the Sigsbee nappe. Overburden deformation was restricted to vertical motion and folding.

Seaward gravity spreading of the brittle wedge occurred when the source layer was thin or denser than sediments, or the tabular overburden was thin. The wedge spread by distal folding and proximal normal faulting. Seaward deposition of new wedges buried the older folds and stretched them. Spreading of overburden wedges with semicircular planform, representing deltaic lobes, formed distal concentric folds, and proximal intersecting concentric and radial normal faults. In nature, such fault patterns may strongly control subsequent channel avulsion and sediment transport.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994