Marsh Foraminifera and Arcellaceans of the Lower Mississippi Delta: Controls on Spatial Distributions

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Abstract
Foraminifera and arcellaceans ("thecamoebians") were examined from 73 surface samples collected to represent four vegetation zones (I-IV) that have been defined in the Mississippi Delta Plain. Previous studies of benthonic foraminifera had not differentiated these environments. Saline marshes (I) are characterized by a vertical zonation typical of most marshes, with a variety of estuarine species in the low marsh and trochamminids in the upper marsh. Brackish marshes (II) are dominated by a completely different set of species, all agglutinated, but the vertical zonation is weak, probably because of the low vertical gradient. Emergent freshwater or intermediate marshes (III) are dominated by arcellaceans but there are significant numbers of foraminifera, indicating episodic marine incursions. The freshwater floating marsh zone (IV) has only arcellaceans. A previous study of arcellaceans living in the lacustrine environment below the floating marsh reveals a different arcellacean fauna than that observed above it. These data suggest that marsh foraminifera have potential application as sea-level indicators in the delta region arid that fossil remains of these protozoans can be used to differentiate coastal vegetation zones in the fossil record.

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