Summary of Drilling Results for the Mississippi Fan and Considerations for Application to Other Turbidite Systems

Abstract

This chapter summarizes the results of Leg 96 sedimentologic studies of the Mississippi Fan. These studies principally describe the youngest fan lobe (deposited during late Wisconsin time) and indicate that a substantial amount of sand was transported through a leveed channel system to the lower fan during that period. Significant amounts of coarsegrained material were also left as a channel lag in the middle fan region. Recovery of these sands was poor, however, and a direct correlation of the Mississippi Fan sections with classic Mutti-Ricci Lucchi facies could not be made. Major submarine slide and debris-flow deposits suggest that a significant portion of the total sediment contribution to the fan might come from the margins of the Gulf of Mexico and not necessarily follow the existing channel system. Good recovery of fine-grained sediment in the upper 50 to 100 m at most sites provides substantial insight on depositional processes of muddy turbidity currents and other density flows in a passive margin, large-scale submarine fan setting. In general, the drilling results on the Mississippi Fan are compatible with seismic stratigraphic interpretations.

A Process Model for the Evolution, Morphology, and Architecture of Sinuous Submarine Channels

“…Drilling of such HARs indicates that they are coarse-grained channel-axis deposits (e.g., Normark et al 1986Normark et al , 1997. Such relationships also suggest that the channels do not undergo significant swing or sweep, because otherwise there would be a meander belt underlying the channel that would be broader than the width of an individual channel, containing the amalgamated deposits of many individual meander bends.…”

“…Sediments include lag deposits (e.g., Normark et al 1986), mud-clast-rich horizons indicative of limited transport and probable levee erosion and collapse (Normark et al 1997), and graded sand-rich beds indicative of turbidity-current deposition (Normark et al 1997).…”

Connections Between Fluvial To Shallow Marine Environments and Submarine Canyons: Implications For Sediment Transfer To Deep Water

“…Examination of Quaternary systems, however, shows that all major submarine fans are fed by submarine canyons (Normark and Carlson 2003). Published examples where canyons feed submarine fans, or fed them during the last glacial period, include the Amazon (Damuth and Kumar 1975), the Mississippi (Normark et al 1986;Weimer 1989), the Zaire (Babonneau et al 2002), the Bengal (Weber et al 1997), the Rhone (Droz and Bellaiche 1985), the Indus (Prins et al 2000), the Nile . The schematic depositional model shows the geography of a hypothetical continental margin.…”

“…Sea Level.-It is well documented that many large fans like the Mississippi (Normark et al 1986), Amazon (Milliman et al 1975;Normark et al 1997), Nile (Ducassou et al 2009), and Rhone (Bonnel et al 2005) are currently mantled with pelagic ooze, and that active deposition ended as global sea level began to rise 15 to 20 kyr ago. Sealevel positions below À100 m would put the shoreline proximal to the heads of these canyons.…”

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“…1) (Normark et al, 1986;Winker and Booth, 2000;Flemings et al, 2006;Sawyer et al, 2007). Specifically we analyzed borehole failure at Integrated Ocean Drilling Program (IODP) Site U1322, which was initiated 1319.5 m below sea level and penetrated to 238 m below seafloor (mbsf).…”