The Mississippi Fan, located in the deeper eastern and central Gulf of Mexico, was constructed during the late Pliocene and the Pleistocene. Eight seismic reflectors can be correlated regionally, dividing the fan into eight fanlobes. These fanlobes are not stacked completely vertically, but show a general migration to the east and to deeper water with time. Each fanlobe basically is an elongated body, characterized by a channel-overbank system, and divisible into a submarine canyon, upper fan, middle fan, and lower fan, each with its own seismic and sediment characteristics. The youngest fanlobe, occasionally the underlying one, was drilled during Deep Sea Drilling Project Leg 96.

In a passive margin setting, in which the supply and sand/shale ratio of the continentally-derived sediment is strongly influenced by eustatic sea-level variations, the sediment normally is stored temporarily on the shelf and the upper slope. Slope failure, likely occurring during the initial rise in sea level, is considered to be the main agent for the movement of the material toward the deeper basin. The submarine canyon, thus formed, continues into the upper fan which is characterized by a major channel formed by the down moving sediment. It continues to act as a conduit and becomes filled passively with fine grained material once bottom transport ceases. At the base-of-slope, the upper fan changes into the aggradational middle fan, which is convex in cross section and has a migratory channel running along its apex. The bottom fill is coarse grained and the overbank areas basically lack sandy material. Seismically, this lag deposit can be seen as an acoustical high-amplitude zone.

The sinuosity and dimensions gradually decrease down-fan. On the lower fan, we see frequent channel shifting, resulting in a band of small sandy channel fills imbedded in an abundance of overbank shales. Lower down the the fan, a channel may bifurcate before terminating. A confined density flow suddenly becomes unconfined and depositional lobes or sand sheets result. The youngest fanlobe, and its underlying one, contain 47% and 65% net sand, respectively.

Although no other modern deep sea fans or ancient turbidite series have been drilled systematically and reported on in the open literature, we feel that the main characteristics of the Mississippi Fan are exemplary for all deep sea fans. Fan sizes and distribution of sands vary considerably although the influences of margin setting, basin shape and size, bottom gradients, sand/shale rations, sea level fluctuations, shelf dimensions, and other parameters, are not yet completely understood. It seems that the sinuous nature of the channel and its migratory aspects are common, and although these systems have a strong similarity to fluvial ones, there may be some sedimentological characteristics that differentiate them from fluvial deposits.

The Mississippi Fan will be discussed in the light of an exploration concept that should be applicable to worldwide occurrences of deep water sands. With the help of public data from a few foreign areas, this concept will be highlighted.

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