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