Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Richard E. Kesel

Abstract

Coastal Louisiana has long served as a laboratory for delta and chenier plain research due to the presence of North America's largest river, the Mississippi. The development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat, combined with a vertical component of submergence acting to preserve the sequence. The evolution of transgressive depositional systems in each of the abandoned Holocene Mississippi River delta complexes can be summarized in a three-stage model beginning with stage 1, an erosional headland and flanking barriers; stage 2, a transgressive barrier island arc; and stage 3, an inner shelf shoal. The current Mississippi River delta model depicts a single Holocene delta plain consisting of six delta complexes sequentially deposited over the last 7000 years by the delta switching process. The delta plain is now viewed as consisting of two separate delta plains deposited at different sea level positions. Termed the Modern and Late Holocene, these two delta plains are separated by a regional ravinement surface several hundred kilometers along strike in extent and bounded updip by a relict shoreline of maximum transgression, the Teche shoreline. The Late Holocene delta plain consists of a set of delta complexes deposited during a sea level stillstand some 6 m below the present, 7000-4000 yBP. A relative sea level rise between 4000-3000 yBP to about present sea level led to the transgressive submergence of the Late Holocene delta plain, generating Trinity Shoal, Ship Shoal, and the Teche shoreline. The Modern delta plain began building seaward of the Teche shoreline about 3000 yBP. The St. Bernard and Lafourche delta complexes and associated transgressive shorelines represent the abandoned portions of the Modern delta plain, separated from the underlying Late Holocene delta plain by the regional Teche ravinement surface.

Pages

226

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