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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 456

Last Page: 456

Title: Lithologic Characteristics of Mississippi Fan: ABSTRACT

Author(s): A. H. Bouma, J. M. Coleman


Deep Sea Drilling Project Leg 96 drilled eight sites on the youngest fan lobe of the Mississippi fan; well logs were run at six sites to complement core recovery. Four sites were drilled on the middle fan across the meandering channel: in a swale, on a point bar, in the channel thalweg, and in overbank deposits. The swale section consists of mud deposited mainly as fine-grained turbidites. The youngest fan lobe extends to 384 m (1,260 ft) subbottom at the overbank site and consists mainly of muds with clayey and silty zones. The gamma log indicates that most of the lithologic zones coarsen upward. Both channel sites have gravel overlain by pebbly muds, which corresponds to a zone of high-amplitude reflectors. The basal coarse unit is approximately 135 m (443 ft) thick. Th channel fill shows a fining-upward sequence from gravel to interbedded sands and silts to sandy muds, and is capped by a 50-m (164-ft) thick homogeneous mud section. The sand section on the point bar side of the channel bend is 30 m (98 ft) thicker than on the thalweg site.

Four sites were drilled on the lower fan lobe, two adjacent to the channel and two near the channel terminus. Well logs indicate 47% net sand for the youngest lobe and 65% for the underlying lobe. The channel generally switches position, building an alternating section of channel fill and overbank deposits.

The channel-mouth depositional lobes coarsen upward, and individual sand layers range in thickness from 0.2 to 10 m (0.7 to 33 ft). They are deposited by turbidity currents.

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