Mechanical Stratigraphy of Salt Induced Structures from Southern Gulf of Mexico

Barrios, Jorge¹, Felipe Audemard² (1) PEMEX Exploracion y Produccion, Villahermosa, Mexico (2) Schlumberger - DCS, Mexico, Villahermosa, Mexico

3D reflection seismic data from the Salina Basin illustrate the style of extensional -contractional nature of the structures triggered by salt movement. Many times these are viewed as independent piercement structures. When evaluated in a regional context these structures are developed from a specific mechanism coupled with the stratigraphy. This tectonic assemblage is defined by the interplay of at least six different decoupling surfaces developed along well defined stratigraphic intervals The sedimentary sequence could be summarized into three major Packages which are rheologically independent. The uppermost Eocene-Recent interval is essentially of siliciclastic nature. The intermediate lime Paleocene – Upper Jurassic (Tithonian) is mainly carbonate and the lower penetrated portion of the Jurassic is made of siliciclastic and evaporites. The seismic character underneath this sequence is interpreted as the autochthonous plastic salt layer. Two salt packages are identified in many places and correspond to the lowermost decoupled levels. The over pressured Tithonian source beds are locally a decoupling surface adjusting the deformation associated with the salt cored structures. The interphase between the competent Mesozoic carbonate and the overlain clastic unit is also a detachment surface at regional scale. The shale rich Oligocene-Lower Miocene interval is an evident decoupling layer associated to a very distinctive chaotic character. The uppermost surface is hosted in the limits of the middle-Upper Miocene. In many places the upper 2 surfaces constitute the sole of shale diapirs. All these surfaces can be viewed as salt weld hosting allochthonous salt masses commonly overlain by rotated sedimentary packages