Depositional Processes of Layered/Laminated Mud Deposits on a Complex Deep-Water environment, Northern Gulf of Mexico
Efthymios K. Tripsanas, William R. Bryant, Niall C. Slowey, Daniel A. Bean, 2004. "Depositional Processes of Layered/Laminated Mud Deposits on a Complex Deep-Water environment, Northern Gulf of Mexico", Depositional Processes and Reservoir Characteristics of Siltstones, Mudstones and Shales, Erik D. Scott, Arnold H. Bouma
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The continental margin of the northern Gulf of Mexico is characterized by a very complex morphology due to the interactions between sedimentary and halokinetic processes. Sediments deposited on the margin during the last glaciation provide an excellent opportunity for the study of depositional processes of fine-grained sediments in a structural complex deep-water environment. This study is based on detailed analysis of long sediment cores and high-resolution geophysical data from two areas of the northern Gulf of Mexico: Bryant and Eastern Canyon Systems and the Atlantis Discovery.
At least three sedimentary provinces existed on the continental margin during the last glaciation. The Mississippi Canyon and Fan resulted from the building of the Mississippi River delta at the shelf-margin during the last glaciation. Turbidity currents flowing through the Mississippi Canyon at this time contributed to the continued development of the preexisting Mississippi Fan.
The Texas and Louisiana continental slope province characterized by numerous intraslope basins. Deposits from the last glaciation consist of hemipelagic sediments interbedded with finegrained (silty-clay to clayey-silt) turbidites that thin and fine downdip. These deposits were produced by low-density turbidity currents that resulted from the depositional segregation (deposition of the coarsest material at the most proximal locations) of large turbidity currents initiated on the outer shelf and/or upper continental slope. Thick (up to 40 m), structureless mud deposits (unifites) on the floors of intraslope basins most likely resulted from the partial deposition of long-lasting (1.5-3 months), low-density turbidity currents.
The continental rise and lower continental slope province of the northwest Gulf of Mexico has fine-grained, layered sediments that are siltier than those of the fine-grained turbidites from the continental slope province, and occasionally reveal a lenticular to wavy nature. The layered sediments are interpreted as deposits of turbulent sediment flows whose site of deposition is controlled by westward flowing bottom currents. The currents pirate the finer-grained sediment load (upper part and tails) of turbidity currents flowing through the Mississippi Canyon to the Mississippi Fan and relocate them within this province.
Turbidity currents were most abundant between 32-28.5 ky BP and 28.5-21.5 ky BP. The first time interval coincides with the development of a major deglaciation event that led to highly increased river discharges. The second time interval coincides with the drop of the sea level to the shelf edge, and the production of shelf margin deltas during the last glacial maximum.
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Siltstones, mudstones and shales have been studied mainly with regard to general transportdeposition processes and clay mineralogy. A small group of investigators, with differing backgrounds, have worked on these fine-grained deposits. Recent studies on deepwater deposits from cores and outcrops indicate that the presence of finer-grained deposits greatly affect the fluid flow properties of deepwater reservoirs. Characteristics and rock properties of these deposits, which resulted from a variety of depositional processes, are just beginning to be understood.