Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

A new Mississippi delta--now in the subaerial growth phase--is building in Atchafalaya Bay, south-central Louisiana, as the result of a natural upstream di-version. Early studies of this event documented gross accretion in Atchafalaya Bay. The present study focuses on subaerial delta lobe responses, stratigraphic development, and sedimentation processes that are incorporated into a model for delta growth. A sedimentological research program undertaken in the eastern half of the Atchafalaya delta has shown that two distinct stages of subaerial delta response are recognizable. The first (younger) re-sponse consists of channel extension, bifurcation, and development of sinuous overbank channels. A latter, more mature response of upstream lobe growth and consolidation becomes dominant once progra-dation through bifurcation ceases. Stratigraphic relationships as interpreted from vibracores show that deltaic sedimentation in Atchafalaya Bay began in the early 1950s. By the early 1960s upper prodelta sediments covered large portions of the bay. The next decade was characterized by coarser grained distal bar development, resulting from an increase in the grain size of suspended sediments transported by the Atchafalaya River. Bay 1972 distributary-mouth bars were present at the heads of major bifurcations. The major floods of the early 1970s beginning in 1973 resulted in rapid subaerial growth as natural levees were formed. From this period through the early 1980s subaerial delta growth continued, although modulated by erosive storm effects.

Pages

161

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