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ABSTRACT: Process Hierarchies along the Northern Gulf of Mexico

LOWRIE, ALLEN, Consultant, Picayune, MS; and SUSAN MOFFETT, Consultant, Picayune, MS

A host of synergistic geologic processes exist on and shape a passive continental margin. These include tectonics (basement, salt, sediment and interactions between), sea-level oscillations, sediment deposition, diagenesis, and changes in fluid-migration routes. Each of process appears to be divisible into hierarchies, as exemplified by the Exxon/Vail sequence stratigraphy model. This hierarchy is based on what is decipherable from industry (10 to 100 Hz) seismic and well-log data. Third and fourth order cycles are documented worldwide. These sequences can be correlated with Milankovich cycles and are common in Quaternary/Neogene sequences.

A similar approach might be used to rank other geologic processes. Tectonic processes might be divided into the following hierarchy: first order tectonics is the basin; second order tectonics is salt/shale diapirism and lateral wedge migration; third order features are suprasalt, growth faults that span the continental margin and sole out in shales/salt tongues and possible inter-sub-salt/basement shear zones; fourth order units can include discrete, secondary antithetic faults, primary and secondary fractures associated with advancing salt/shale; fifth order and finer tectonic features descend into shattered sediments where local heterogeneity results from original deposition irregularities and subsequent differential compaction, hydrocarbon pockets, local migration and diagenetic routes.

During preliminary regional exploration, with specific geology yet unmapped, it is prudent to sketch what processes, and their dimensions, periodicities and vectors can be operating in a reconnaissance area. This knowledge would be invaluable to deriving an evolutionary history in an area of interest.



AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas