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Gravitational Salt Tectonics Triggered by Deposition of Turbiditic Lobes: a New Experimental Modeling Approach with Applications to Salt Tongues in the U.S. Gulf of Mexico

Sellier, Nicolas 1; Vendeville, Bruno C.1
1 Laboratoire Geosystemes- CNRS 8157, Universite de Lille 1, Villeneuve d'ascq, France.

So far, there have been two drastically different approaches at modeling the effects of deposition of clastic sediments wedges along passive margins. First, the stratigraphic approach models sediment transport and deposition, focusing on the resulting stratigraphic architecture, but neglecting the impact of syndepositional deformation. Many flume experiment simulating turbidity deposits were designed to understand the stacking patterns of deep-sea turbiditic fan systems. But most experiments did not account for syndepositional deformation. Second, there has been some extensive experimental and numerical work by structural geologists on deformation of sediment wedges above weak substrates (salt or shale), but using rather crude and simple ways of sedimentation processes (by adding episodically one sediment layer uniformly, regardless of the potential influence of the bathymetric relief on depositional patterns).

We designed a new tectono-stratigraphic modeling tank that comprises a channel connected to a main basin. The basin can be filled with different kind of substrates either rigid (sand) or viscous (silicone polymer, simulating a salt layer of varying length and thickness). A mixture of fine-grained sand powder and water (50 to 150µm in diameter) were released, then channeled into the basin.

We investigated the effect of depositing several consecutive turbiditic lobes on the deformation of a viscous salt body. The dynamics of turbidity currents lead to deposits whose thickness varied laterally : thick in the proximal area, and thinning progressively distally, thus creating a gentle regional surface slope. In addition, salt’s response to even minor local differential loading was vigorous. In models, lobe deposition generated sub-marine dunes sub-millimetric in scale. The underlying salt immediately subsided beneath each sedimentary ridge, and rose passively in between the dunes. Furthermore, with growing maturity of the sedimentary lobe, regional spreading/collapse of the entire overburden started. Spreading induced shortening at the distal salt basin’s edge, and radial extension in the proximal area, which generated multidirectional grabens and normal faults, in a ROHO fashion, and associated salt ridges that evolved into piercing diapirs.

We also conducted a series of systematic experiments varying the length and thickness of the salt body, as well as the sediment input. The outcome varies from ROHO-like structures to counter-regional faults.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009