Characterization and Depositional History of Muddy Lithotypes, Mississippi Fan

Kevin P. Lanigan, James M. Coleman

Previous work has shown that the Mississippi fan contains an abundance of predominantly fine-grained terrigenous clastics whose gross sediment properties indicate the major mechanisms of emplacement to be redeposition by density currents and debris flows. However, details of the way in which these and other depositional processes affect the accumulation of fine-grained sediments is still poorly understood, partly because of the general similarity that muds deposited by different mechanisms often display.

Image-processing techniques, applied to x-ray radiographs to quantitatively analyze the fine-scale structure of previously undifferentiated muddy intervals, have resulted in a subdivision comprising several lithotypes. Additional sedimentological analyses, including grain-size and x-ray diffraction studies, support this subdivision and have provided a suite of characteristics by which each lithotype can be identified.

A study of the microscale structures (several microns to a few centimeters) has enabled an evaluation of specific processes responsible for deposition of the fine-grained fraction. This has revealed features such as normal and reverse grading, minor scouring, a variety of microlamination types, and bioturbation.

Results from application to recent mississippi fan sediments have improved understanding of deep-water fine-grained sediment processes and provide encouragement for further testing on other muddy depositional systems, including the potential applicability to ancient sediments.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.