Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The Mississippi Delta consists of six major Holocene deltaic complexes, that each had a life-span of about 1500 years. Emphasis of this study is on autochthonous peats of Barataria Basin, a large-scale interdistributary basin, between levees of the LaFourche and St. Bernard/Plaquemine deltas. A 6 m. thick set of lithostratigraphic units constitutes the aggradational basin-fill. Organic-rich beds occur in three phases, each representing an accumulating period that was interrupted by subsidence and the influx of detrital clastics from renewed nearby fluvio-deltaic sedimentation. Peats accumulated in eutrophic, non-domed environments in fresh water swamps and (often floating) marshes and average 81.7% organic matter by dry weight. They occur in the same stratigraphic unit as organic-rich beds and are predominantly situated on top of clays and organic-poor beds. In central Barataria Basin, peat beds are laterally discontinuous, contrasting with more continuous ones in the upper Basin. This difference reflects greater subsidence and overbank flooding in the central Basin, compared to the upper Basin. In the upper Basin, accumulation rates balanced with subsidence, whereas in the central Basin, fault-induced subsidence rates were higher, creating a flood-prone depression. Quantities of organic-rich material and true peat, as well as quantities of peat and organic-poor material are inversely related. The latter correlation indicates either one of two possible settings: (1) more peat accumulated on top of organic-poor material, because organic-poor beds provided a base for plant growth and a supply of nutrients; (2) organic-poor material accumulated preferentially on top of peat because peat-accumulating areas eventually form flood-prone topographic lows. Relatively low mean organic matter content of peats in the Mississippi Delta is influenced by botanical parent material and short-term detrital clastic influx. Thickness and lateral continuity are restricted by subsidence and accretion rates, marine inundation and long-term effects of detrital clastic influx.

Pages

281

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