Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

This study of peats and associated sediments from a portion of the Lafourche delta had four objectives: (1) to develop methods for reconstructing paleoenvironments of buried peats and their associated sediments from core material; (2) to apply these paleoenvironmental methods to reconstructing the history of sedimentation; (3) determine the relationships between peat formation and deltaic environmental conditions; and (4) to reconstruct the development of an interdistributary basin during the Lafourche deltaic episode. Three cores and several auger derived samples were recovered from a portion of the Lafourche delta, southeast Louisiana. Paleovegetation analysis of the cores was accomplished by comparing the seed assemblages of the buried peats to the modern-day floral community structures (marsh types) of the coastal Louisiana peat-forming environments. Since salinity is the most important floral ecological regulator in the coastal Louisiana marshlands, paleosalinity indicators were developed utilizing marsh and estuarine foraminifera (mesohaline indicators), and gemmules (oligohaline indicators). Chemical paleosalinity indicators were also tested. The important conclusions of the study are outlined below: (1) Analyses of the three study cores revealed progressive increases in salinity from the bottom of each core to the top. Coincident with these salinity increases were changes in marsh types from fresh marshes towards the base of the cores, to intermediate and brackish marshes in the middle of the cores, and saline marshes at the surface. (2) The duration and magnitude of salinity variations through time were the most important factors controlling the occurrence and organic matter content of the intermediate and brackish marsh deposits. (3) Results of the maceral analyses from the cores revealed mechanisms of organic matter sedimentation, and elucidated environmental conditions during deposition and early diagenesis. (4) The chemical paleosalinity indicators tested were unsatisfactory due to the vertical migration of fluids from the surface sediments. (5) A reconstruction of interdistributary basin formation was developed utilizing results from the paleoenvironmental core data and auger sediment descriptions. (6) A peat classification system, based on the results from this study, was designed to integrate descriptions of peat floral composition with salinity and measurements of organic matter type.

Pages

313

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