Sedimentary Structures Associated with Mississippi River Delta-Front Deposits: ABSTRACT

Hydraulically controlled sediment-distribution patterns in Mississippi River delta-front environments are continually being modified being modified by mass-movement processes, and sediments are constantly being redistributed. Numerous deformational features have been identified and mapped by the combined use of side-scan sonar and high-resolution seismic profiles coupled with accurate navigational control. Major deformational features include diapirs, faults, slumps, and various types of complex mudflows that have many geomorphic components, from slumped upslope source areas to distal overlapping depositional lobes. As a result of mass-movement processes, sediments are redeposited as blocks, flows, and completely remolded masses, all of which can occur on a variety of sca es. Although surface and subsurface expressions of deformational features are commonly clear, sedimentary structures and inclusions characteristic of each major deformational form have not been systematically evaluated. By means of X-ray radiography, subtle inhomogeneities in texture and density changes associated with post-depositional chemical products describe structures and inclusions typical of deformed sedimentary sequences. Various types of fractures and microfaults, sedimentary gas expansion voids and migration paths, flow structures, convolute bedding, grain flows, diagenetic features, and organically derived structures are arranged in combinations that define components of a complex mudflow system. Using the structures and inclusions found in delta-front sediments, criteria have been developed for differentiating disturbed and nondisturbed sedimentary sequences within the delta-front environment. End_of_Article - Last_Page 1567------------