Abstract:
Planktonic foraminifera were used as the major proxy in a paleoenvironmental reconstruction at ODP Site 898A on the Iberian Abyssal Plain. Sections 7H through 19X were examined. The period of study spanned nannofossil zone NN19a through nannofossil zone NN19e (Upper Pliocene to Middle Pleistocene). Planktonic foraminiferal evidence suggests that two distinct paleoenvironmental zones exist within the period of study. Nannofossil zones NN19a through NN19c are dominated by the transitional and subtropical taxon Orbulina universa and Globorotalia inflata, whereas NN19d and NN19e are dominated by the sub-polar taxon Neogloboquadrina pachyderma. The lithology of much of the core studied is dominated by turbidite sequences (Sawyer, et al., 1994), thus explaining the preservation of the planktonic foraminifera tests at this site, which is well below the calcium carbonate compensation depth. Original site of deposition and taphonomy have been considered in the paleoenvironmental interpretation. The shift indicated by the planktonic foraminffera, from a warm water mass assemblage to a cold water mass assemblage is also indicated other microfossil proxies (McCarthy and Mudie, in press; and McCarthy and Scott in prep). These data complement the data from other sites in the western North Atlantic, (DSDP 604, 607, 613), indicating a significant paleoceanographic change at approximately 1.37 Ma. This change is interpreted to be caused by a "tightening" of the subtropical gyre in the North Atlantic (McCarthy et al., 1996). A shrinking of the gyre would explain the influx of colder water on the Iberian continental margin at 1.37 Ma.