Size and Fourier-shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the Dallol Bosso in Niger. Factor analysis of grain-size distributions gave four sand end-members that can be related to fluvial transport dynamics operating when the sediments were initially deposited. The medium to fine (and more angular shaped) sand fractions are being reworked by wind. Aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape. Although grossshape characteristics (lower harmonics of Fourier series expansion) indicated a common source rock for all sands, the aeolian sands were well rounded whereas the fluvial sands tended to be more angular (upper harmonics of Fourier series).
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.
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