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Using Ultrahigh-Resolution 3-D Seismic Data to Better Delineate Mass-Flow Deposits Within Complex Salt Structures


The Northern Gulf of Mexico salt overburden is a complex and tortuous network for sediment transport and associated gravity driven processes where many fairways and ponded mini-basins consist of >50% mass-transport complexes (MTCs) and debris-flow deposits. These MTCs have a marked range of depositional styles, internal and external deformation characteristics, and resultant hydrocarbon seal and trap potential. A newly acquired (2014) ultrahigh-resolution 3-dimensional (UHR3D) seismic-reflection survey shot over the southern flank of the Mississippi Canyon images three distinct salt diapir and their intra-diapiric sediment fill. The 3D survey covers 416 km2 in the southwest portion of the Mississippi Canyon protraction area with a 3.13 m by 6.25 m line spacing and a 0.5 ms sample rate down to 4 seconds (Two-way Time) below sea-level. Seismic frequencies in the zones of interest range from 50-200 hz. This UHR3D survey allows for greater detailed mapping of individual MTCs and their healing-phase architectural elements than were previously available in conventional commercial seismic-reflection data. Early interpretations identify two southern mini-basins, which are bounded by salt, and a third northern mini-basin, which is partially open to the north into the greater Mississippi Canyon. Numerous hydrocarbon seeps and mounds are observed on the seafloor and seismically obscured vertical migration pathways indicate an active petroleum system. Several MTCs are interpreted within each mini-basin where; 1) position of sediment maximum thickness, 2) orientation of scour marks, 3) direction of supra-deposit channelization, and 4) style of internal seismic character are recorded. The stratigraphic order of the flows indicates mass-transport emplacement direction and position of maximum accommodation relative to the salt diapirs. More extensive analysis of the observed data will link the relative timing of diapirism of the three salt bodies to each other by extrapolating the variations in emplacement position of individual MTCs and their flow directions within the three mini-basins. The UHR3D enhances the ability to accurately define individual MTCs and better characterize the lithologic heterogeneity and stratigraphic relationships of MTCs against active salt diapirs having broad implications for the pathways of fluid migration, hydrocarbon sealing, and stratigraphic trapping potential of these large marine depositional features.