ABSTRACT: Late Pleistocene to Recent Sedimentation and Stratigraphy of the Gulf of Mexico Outer Continental Shelf, Offshore Louisiana

James H. Crane, R. E. Sheriff, W. R. Dupre

The Late Pleistocene to Recent sedimentation and stratigraphy of the Louisiana outer continental shelf was studied using sediment from a 480-ft engineering boring and hazard survey data from the Eugene Island Block 366 area. Interpretation of these data provided information on the changes in sedimentation and stratigraphy that occurred during the rises and falls of sea level over the last 300000 yr.

The major findings of this research include the following. (1) A sequence of condensed sections (rising to high sea level) and expanded sections (falling to low sea level) along with strong evidence for four major drops in sea level over the last 300000 yr. (2) Condensed sections characterized by fine-grained sediment containing significant amounts of diagenetic pyrite, benthonic and planktonic foraminifera, and echinoid fragments; CaCO₃ content decreasing downward; the percentage of quartz and feldspar grains increasing downward; the presence of a basal shell concentration with a glauconitic sand found in unit 7; and seismic facies dominated by sheet drape (hemipelagic deposits). (3) The existence of a meltwater facies (associated with high glacial meltwater influx from th Mississippi River) and a highstand facies (associated with no significant glacial meltwater influx) with the condensed sections. (4) Expanded sections characterized by a higher percentage of coarse material in the sediment than in the condensed sections; exposure surfaces at the top of the section; erosional truncation of seismic reflections; coarsening-upward sequences; rare microfossils, diagenetic, pyrite, and echinoid fragments; CaCO₃ increasing downward; wood fragments, muscovite mica, and biotite mica that are not found in the condensed sections; and seismic facies that include oblique progradational (delta), sigmoid progradational (low-energy outbuilding), and mounded chaotic (mass transport facies). (5) The existence of sedimentary magnetite in the expanded sections a d associated magnetic anomalies that were mapped.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990