Paleogene calcareous nannofossil magnetobiochronology: Results from South Atlantic DSDP Site 516

Abstract

The detailed study of an expanded Paleogene section with abundant, moderate to well preserved calcareous nannofossils from South Atlantic DSDP Site 516 has resulted in a precise correlation of most calcareous nannofossil markers with the magnetostratigraphy. Many nontraditional datums have also been documented and correlated to the magnetostratigraphy. Comparison of the results from Site 516 with those of previous studies from other areas enables a critical evaluation of the accuracy, synchroneity or diachroneity of the species events over geographically long distances. Of special significance is the correlation for the first time of the stratigraphic ranges of Chiasmolithus gigas and Rhabdosphaera gladius with the magnetostratigraphy. Other important results include the following: first occurrence (FO) of Cruciplacolithus primus, 66.3 Ma; FO Chiasmolithus danicus, 65.6–66.0 Ma; FO Prinsius martinii, 65.5–66.0 Ma; FO Heliolithus kleinpellii, 59.8–61.6 Ma (probably diachronous); last occurrence (LO) of Tribrachiatus orthostylus, 51.0–54.8 Ma (unreliable); FO Chiasmolithus gigas, 47.4 Ma; FO Reticulofenestra umbilica, 44.6 Ma; LO Chiasmolithus gigas, 44.4–46.8 Ma (diachronous); LO Nannotetrina fulgens, 44.2 Ma; LO Chiasmolithus grandis, 40.0–41.6 Ma (probably diachronous); FO Chiasmolithus oamaruensis, 39.8–40.4 Ma (unreliable); FO Isthmolithus recurvus, 39.5 Ma; LO Reticulofenestra reticulata, 37.6 Ma; LO Discoaster saipanensis, 36.4 Ma; end acme of Ericsonia subdisticha, diachronous; FO and LO Sphenolithus distentus, unreliable; and LO Reticulofenestra bisecta, 24.0 Ma.