Deep Structure and Stratigraphy, Southern Louisiana Additions

David J. Hall, Kenneth J. Thies

Detailed interpretation and mapping of over 10,000 km of new 80 fold seismic data integrated with key deep biostratigraphic and well log information have provided a new understanding of the geological history of the southern Louisiana shelf. Sequence by sequence backstripping of a grid of depth-converted balanced cross-sections quantitatively accounts for 1) protracted synsedimentary deformation (folding and faulting), 2) incremental compaction and 3) changes in shape and area of ductile salt layers in an overall extensional terrane. Two major stages of deformation are developed: 1) An early period of salt sheet spreading with rapid, shallow widening of largely passive diapirs that initiated by downbuilding over autochthonous salt, 2) Subsequent salt evacuation from empla ed sheets accompanied by pervasive synsedimentary extension. The two resulting structural regimes are disharmonic, separated by a complex set of features variously characterized as syndepositional normal faults, thin residual salt masses, salt and/or fault welds. Both Upper Miocene and Lower Pliocene sequences and systems tracts have been discordantly intruded by the spreading salt sheets. Although the structural/stratigraphic relationships are inter-related and complex, the identification of sequences beneath thin salt and salt/fault welds is constrained by careful extrapolation from known, relatively simple basins toward more complex, undrilled areas. Quantitative depth reconstructions of the network of control sections based on the interpretations rigorously verify geometric viability and provide a powerful reservoir predictive tool for each of the eustatic cycles studied.