Abstract
A palynological study of modern sediments from subaerial environments of the Mississippi Delta plain shows that palynomorph assemblages are characteristic of salinity and depositional environment. Pollen assemblages closely reflect the local vegetation that characterizes each of four salinity zones, providing usefid analogues for Quaternary reconstructions of regional deposits. Within transgressive systems (marshes in interlobe basins), pollen concentrations calculated on the basis of sediment weight increase from distal to proximal toward terrestrial (headland) vegetation sources. This parallels recognized patterns in subaqueous environments in which abundances decrease seaward away from shore. However, abundances of extraregional pollen (from sources outside the delta plain) do not vary systematically from proximal to distal parts of the delta. Concentrations of extra-regional pollen vary with respect to proximity to sources as well as magnitude of the inputs (aerial, fluvial, and tidal). Proximal freshwater marshes and distal salt-water marshes have a greater proportion of regional and extra-regional pollen, whereas marshes of intermediate salinity have the lowest abundances of extraregional pollen. A general palynological model can be constructed to distinguish subenvironments of the delta plain using four attributes: presence of microforaminifera, abundance of reworked pollen, palynomorph concentration, and the ratio of regional to local pollen types. This model may be applicable to other large marine deltas.
