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Salt Movement in the South-Central Walker Ridge

Hunsdale, Robert 1
1 StatoilHydro GEX NA GOM, Houston, TX.

Over the past 15 years a number of models for the thin skinned evolution of the Gulf of Mexico (GoM) have been put forward describing the relationship of the present day Sigsbee Allochthon to the precursor Louann authochthonous salt basins. Models involve intermediate stage allochthonous sheet development (notably in the late Palaeogene and early Neogene) and early salt nappe or para-autochthonous sheet extrusion (through the Mesozoic and into the early Palaeogene). Models have focused on the western and eastern GoM where seismically identified foldbelts mark the compressional distal end of the thin-skinned deformation systems. Here the compressional foldbelts are linked through translational domains to time equivalent updip extensional domains providing a “balanced” structural picture of thin-skinned salt movements across the basin margin. Less attention has been paid to the central GoM (central Keathley Canyon to central Walker Ridge areas) where although shelfal and shelf edge extension is recognisable, the equivalent distal portion of the thin-skinned deformation system is characterised by a more enigmatic, and not clearly compressive, tectonic style.

In the central Gulf structural style varies with salt cored folds (which form as a result of both compression and salt withdrawal) found in conjunction with diapirs and salt walls (which are either vertical or verge towards the basin) and other salt styles such as counter-regional fault systems and bowl weld systems. Salt cored folds tend to be periclinal, have low fold axes length ratios and are less well organized than those seen in the Alaminos Canyon and Atwater Valley areas. Salt wall trend is variable, with early counter-regional style geometries forming along walls orientated wnw-ese and salt stock canopy development more often associated with diapir-salt wall systems that trend nearer n-s. Based on the observed structural styles is it is difficult to characterise this part of the deepwater margin as solely compressional.

Using Mesozoic to early Neogene isochore and depth structure maps salt movements in the south-central Walker ridge are described. The observations made are used to suggest why salt related structural geometries in this area vary from the well defined compressional zones seen further to the west and east.

 

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