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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Northern Gulf of Mexico Continental Margin Deformation Proposed to Be by Simple Shear with Regional Basal Horizon Terminating Under Yucatan
(1) Consultant, Picayune, MS.
(2) Earth Studies Group, New Orleans, LA.
The northern Gulf of Mexico continental margin from Little Rock, Arkansas, to Sigsbee Escarpment is intermittantly migrating basinward via extensional faulting. Motion-tectonice loci is along the shelfbreak-slope. The sedimentary wedge is underlain by Louann Salt. This portion of detachment is denoted as a "salt-floored basin," operating semi-independently of remaining Gulf sediments, salt serving as an ideal 'lubricating" and separating detachment surface.
'Simple shear' is an idealized regional thin-skinned 3-D constant volume deformatiom mechanism, often characterized by normal faulting in the hanging wall volume. The foot of sliding surface separating hanging wall and foot wall volumes may terminate beneath a counter-dipping wedge. Defined here, a single simple-shear mechanism describes evolution of 1200 km of northern Gulf margin. Maximum sediment thickness is 17-19 km wich at present coincides with the juncture of continental and oceanic crust and southern limits of Sigsbee Salt.
Presently, basinward of the salt canopy, depth to oceanic crust shallows with thinner sediment loading. The simple shear decollment is apparently interrupted by younger Gulf crust. Closer to Yucatan, with greater sediment loading, the simple shear detachment surface may continue its southward dip, before again disappearing beneath the mobile Yucatan continental fragment and interloping younger Caribbean crust.
Thus, with a single decollment, simple shear can explain Gulf-wide tectonics from Arkansas to Yucatan and probably to Colombia, a restored distance greater than 1800 km. With active mid-ocean and back-arc seafloor spreading, younger ocean crust today interrupts and complicates the Early Jurassic simple-shear detachment.