Upper Cretaceous strata of Mississippi contain diverse nannofossil floras. Samples taken from the upper Bluffport Marl, Ripley Formation, and lower Prairie Bluff Chalk of Kemper and Oktibbeha Counties, Mississippi, were examined to determine nannoplankton abundances and occurrences.

In the strata examined, 117 nannofossil species were recognized and 9 biostratigraphic zones were delimited of which 6 are new. The intervals of 3 previously described zones, the Tetralithus aculeus, Chiastozygous initialis, and Lithraphidites quadratus zones have been modified.

In these sections, the Bluffport-Ripley contact could not be delineated using nannofossils but the unconformable nature of the Ripley-Prairie Bluff contact could be recognized by significant nannoplankton changes.

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