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Examination of extensive multichannel and single-channel seismic data across the Mississippi Fan, Gulf of Mexico, reveals that at least 7 seismic sequences comprise the upper Pliocene-Pleistocene section of this giant fan. These sequences are divided into 2 groups based on continuity and amplitude of reflectors. The lower 3 sequences are generally characterized by high-amplitude, parallel to subparallel, continuous reflectors overlain in places by a hummocky clinoform reflection configuration. The reflection patterns suggest distal turbidites deposited in a relatively low-energy environment. In contrast, the upper 4 sequences are generally thicker and characterized by regionally extensive chaotic units interbedded with thin, high-amplitude, parallel to subparallel reflect on packages. The chaotic zones grade laterally into more continuous, parallel to gently diverging reflection patterns, probably a lower energy, more distal turbidite facies. Isopach and structure maps of each sequence indicate a seaward and eastward migration in the Pliocene-Pleistocene depocenter during fan development.
Channel, levee, slump, turbidite, and hemipelagic deposits are interpreted within each sequence. Channel/levee deposits are extensive, showing great variability in their morphology and distribution. On the upper fan, the channels are large with well-developed levee sequences. On the middle and lower fan, the channel sequences are smaller, confined mainly to the apex of lobes, and show little evidence of migration and abandonment during lobe development. Slumping off the slope apparently contributed a significant percentage of the material deposited on the upper fan. In addition, the truncation of prominent reflectors and the mounded, chaotic and diffracted patterns on the middle and lower fan suggest that slumping was continually active during fan development.
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