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Apps, Gillian M.1, Frank J Peel1
(1) BHP Billiton Petroleum, Houston, TX

ABSTRACT: The Relationship between Sequence Stratigraphy, Depositional Systems, Salt Tectonics, and Compressional Folding in the Central US Gulf of Mexico

It is commonly accepted, but rarely demonstrated, that there should be a relationship between: (i) Eustacy/sequence stratigraphy (ii) Depositional systems on the continental slope, and (iii) Phases of salt movement and compressional tectonics. This relationship is well illustrated in offshore Louisiana, where an excellent data set of seismic and well data defines the structure and stratigraphy in the continental slope. Regional mapping allows us to break the stratigraphy down in to its components, from the megasequence to the 5th order sequences.
The most important control is exerted by 2nd order sequences, which occur on a 2-3Ma timeframe; 3rd-5th order sequences occur too fast to influence salt or compressional tectonics.
Dramatic shifts of depositional systems occur during 2nd order highstands; the center of mass of the depositional system shifts updip to the shelf/upper slope, the lower slope is abandoned, and the whole system may shift laterally by avulsion. During these highstands, structure growth outpaces sedimentation, creating significant bathymetric relief. Salt canopies have time to initiate and spread. Lateral shifting of the updip depocenter can cause a radical change in the downdip structural style.
In the succeeding 2nd order lowstand, deposition is once more focused on the slope, but it finds a very different world from the one it abandoned. Topography has developed which strongly influences sediment pathways. Ponded salt-withdrawal basins in the mid-slope must be filled before sediments can spill to the lower slope. Consequently, initial lowstand deposits are strongly topographically influenced, but this effect wanes as the topography is overwhelmed.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004