322 Early Pliocene benthic foraminifers from the Salina Basin, southeastern Mexico

This study comprises the taxonomic, biostratigraphic, and paleoecologic analyses of early Pliocene foraminifers in the western Salina Basin of southeastern Mexico. Three “biozones”, the Encanto, the upper Concepcion, and the lower Concepcion (all previously designated as formations), lying within a 600 sq km area centered around Acayucan, Veracruz, are the focus of this study. Ranges of key planktic foraminifers and calcareous nannoplankton indicate that these “biozones” belong to Neogene Zones 19 and 20 of Blow (1969).

Collections of benthic foraminifers from the Encanto and Concepcion “biozones” contain 212 taxa assigned to 108 genera. The following species are new: Chrysalogonium spinastelliferum, Discorbis? olutensis, Ehrenbergina olmeca, and Oolina sayulensis. Ninety-one percent of the species described in this study occur in Pliocene sediments in the subsurface continental shelf of Louisiana and Texas. Many Pacific taxa are recorded for the first time from the Gulf of Mexico coastal plain.

Three assemblage zones, based on key benthic foraminifers, are proposed. The Melonis affinis-Uvigerina hispida Assemblage Zone, having a middle to upper bathyal paleobathymetry, is equivalent to the Encanto “biozone”. This biozone is overlain by the marginulinopsis hispaniolana-Anomalinoides nucleatus Assemblage Zone, which is equivalent to the lower Concepcion (upper bathyal to outer neritic). The youngest unit, the Bolivina imporcata -Saracenaria nuttalli Assemblage Zone (outer neritic to middle neritic), is equivalent to the upper Concepcion.

The gradual decrease in paleo water depth from upper bathyal to middle neritic, as indicated by changes in the foraminiferal assemblages, supports the probability of a Salina Basin uplift coincident with the uplift and early Pliocene closure of the Isthmus of Panama at 3.5 my.

B. Kohl

Pages: 173, 36 pls., 18 text-figs., 1 table, appendix