SEDIMENTOLOGY AND PETROLOGY OF THE LATEST PLEISTOCENE MISSISSIPPI FAN LOBE: RESULTS FROM DSDP LEG 96

The Deep Sea Drilling Project (DSDP) Leg 96 has been one of the most important sources of data for understanding the sedimentology and stratigraphy of the deep Gulf of Mexico. Cores from nine DSDP Leg 96 drill sites on the Mississippi Fan provided samples from which sedimentologic-petrographic characteristics of the fan’s major depositional environments were determined. Samples analyzed from the middle fan were derived from (1) channel fill, (2) overbank deposits, and (3) slumped marginal-fan sediments. From the lower fan, samples were analyzed from (1) channel fill, (2) overbank deposits, and (3) channel mouth lobes. Methods used included X-ray radiographs, SEM and thin-section photo micrographs, and X-ray diffraction analysis.

Gravels of the middle and lower fan channels were found to be composed of polycrystalline quartz and faceted chart. Channel sands of both the middle and lower fan as well as the lower fan channel-mouth lobes consisted of feldspathic litharenites, sublitharenites, and subarkoses composed of quartz and subordinate amounts of feldspar, mica, and heavy minerals plus reworked foraminifera tests, shell fragments, glauconite, and abundant wood fragments. The upper channel fill and overbank deposits were composed of finely laminated clays, silts, and fine sands. Authigenic clays and other diagenetic products, including gypsum, pyrite, calcite, and dolomite were found in these fine-grained facies of the upper channel fill and overbank. However, the sands of the channels and channel mouth lobes contained few diagenetic products and have high porosities and therefore have excellent hydrocarbon reservoir potential.