BIOMAGNETOCHRONOLOGY OF MIDDLE EOCENE PLANKTONIC FORAMINIFERA

Planktonic foraminiferal biostratigraphy provides an important tool for constraining the timing of dynamic changes through the middle Eocene. We examine planktonic foraminiferal assemblages from Ocean Drilling Project (ODP) Leg 171B, Site 1051, Blake Nose in the western North Atlantic Ocean. Planktonic foraminifera are abundant, with diverse assemblages. Quantitative biostratigraphy was conducted on planktonic foraminifera from 119 to 369 meters below sea floor in Hole 1051A. This interval corresponds to magnetochrons C21n to C18r. All planktonic foraminifera are well preserved (although recrystallized), and assemblages are diverse with common Acarinina, Globigerinatheka, Subbotina, and Turborotalia.

Quantitative biostratigraphy reveals highest and lowest occurrences of key marker taxa includingTurborotalia frontosa, Guembilitrioides nuttalli, Morozovelloides aragonensis, and Globigerinatheka kugleri. Other secondary bioevents are also well constrained including Morozovelloides lehneri and several acarininid species. Our study allows for significant revision and recalibration of planktonic foraminifera SubZones E7b through Zone E11.