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Facies Comparison of Modern Mississippi Fan and Ancient Fans

Ganapathy Shanmugam, John E. Damuth, Richard J. Moiola, Suzanne O'Connell

Cores from Deep Sea Drilling Project Leg 96 were examined to determined whether the Mutti and Ricci Lucchi turbidite facies associations observed for ancient submarine fan environments are present in the modern Mississippi Fan. Cores from the channel floor in the middle part of the fan (Sites 621, 622) comprise abundant slumps and debris flows (facies F), conglomeratic and sandy turbidites (facies A, B), and occasional contourites. Adjacent levee (overbank) deposits (Site 617) consist of slumps (facies F) and ripple-laminated silty turbidites (facies D?, E?). In the Mutti and Ricci Lucchi scheme, facies F is not considered typical of levee (overbank) deposits. Sites 614 and 615, which are located in the outer part of the fan, supposedly cored depositional lobes at the ter ination of the most recent fan channel. These cores, however, contain only thick channelized sandy turbidites (facies B?), slumps (facies F), and some contourites, and do not exhibit nonchannelized, thickening-upward trends or facies C and D, which are considered characteristic of ancient fan depositional lobes.

In our opinion, Leg 96 cores do not display facies associations typical of analogous ancient fan environments. That is, the entire Mississippi Fan appears to consist of channel and levee (overbank) sequences with no development of outer fan lobes. If these observations are confirmed when other modern fans are extensively cored, ancient submarine fan models will require extensive revision.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.