SALT KINEMATICS, DEPOSITIONAL SYSTEMS, AND IMPLICATIONS FOR HYDROCARBON EXPLORATION, EUGENE ISLAND AND SHIP SHOAL SOUTH ADDITIONS, OFFSHORE LOUISIANA

Abstract

ABSTRACT Detailed interpretation and mapping of more than 10,000 km of 80-fold 8-second recent seismic data and preliminary interpretation of 2500 km of new 15-second, 6 km streamer data provide a new understanding of the kinematic and stratigraphic development of the southern Louisiana shelf. The new data reveal elongated subsalt basins, separated by nearly vertical salt welds and residual salt walls. Sequential back-stripping of balanced depth sections suggests that the walls were initiated by differential loading of overburden depotroughs and grew primarily by down-building. Sand fairways developed between the salt walls with a primary sediment transport direction from the northeast to the southwest. Time structure maps of the MDB (Miocene D. Berggreni) sequence boundary (top of the Miocene) reveal a subsalt and subweld structure disharmonic with a much younger, extremely extended section. The younger section is characterized by backward-rotated hanging walls overlying listric growth-faults. We propose that the original extent of salt sheets emplaced near the sea floor can be defined by the current location of the extended overburden which formed as a result of secondary salt sheet withdrawal. Windows through the residual salt and salt welds, and a few key deep wells which have penetrated the welds provide biostratigraphic control on the timing of the salt/sediment interactions. The vertical welds and walls, coupled with residual salt sheets and horizontal welds, form a network of surfaces separating largely isolated basins. Each basin seems to have developed independently due to varying episodes of local salt motion. The Mahogany discovery, Ship Shoal 349, is an example of sands trapped against the flank of a northeast-trending nearly vertical salt weld. Maps of the former salt sheets associated with salt walls and welds and maps of subsalt structure below the sheets and welds define prospective areas analogous to Mahogany. Additional attractive structures were also localized by salt-sediment interactions.