ABSTRACT

Classic studies of the Mississippi River by Fisk (1944) emphasized the concepts of a single Holocene delta and Substratum/Topstratum deposits infilling the incised valley. Subsequently, work by Kolb and Van Lopik (1958) and Frazier (1967) continued to emphasize the single Holocene delta concept and further refine delta complex chronology. Over the last decade, an extensive new geologic database of high resolution seismic profiles, deep borings, vibracores, and radiocarbon samples has lead to the recognition of multiple deltas that can be organized into a new late Quaternary model subdivided into lowstand, transgressive, and highstand systems tracts.

The last Wisconsian Mississippi River incised a deep alluvial valley across the continental shelf floored by coarse-grained substratum deposits which represent a lowstand systems tract shelf-margin delta. The Topstratum deposits can be subdivided into a transgressive systems tract and a highstand systems tract. As the Wisconsian glaciers melted and the Holocene transgression ensued, the Mississippi River filled its incised valley with a series of retrogradationally stacked shelf-phase deltas (Outer Shoal and Ship Shoal deltas). The highstand systems tract was recognized when the delta stacking pattern changed from retrogradational to progradational (Modern delta). This new late Quaternary model emphasizes the importance of autocyclicitic and allocyclicitic processes with infilling the incised Mississippi River valley with a shelf-margin delta and a series of shelf-phase deltas.

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