Upper Paleocene-lower Eocene radiolarian biostratigraphy of the San Francisco de Paula section, western Cuba: Regional and global comparisons

In response to a growing need to define the Paleocene/Eocene boundary and r ecord the events which immediately preceded and followed it within a 5 my s pan, the San Francisco de Paula section of western Cuba was evaluated for i ts potential as a boundary stratotype. Radiolarians, reported in previous s tudies by Cuban geologists as a major component of the faunal assemblages i n this section, have been recollected and reanalyzed to determine their str atigraphic utility for recognition of the Paleocene/Eocene boundary in Cuba . On the basis of this and other recent microfossil studies of the San Fran cisco de Paula section, it is now known that the Paleocene/Eocene boundary in this succession is within an unconformity. Its placement herein is based on the highest occurrence of the planktonic foraminifera Morozovella velas coensis (Fernandez-Rodriguez et al. 1999, this volume). Radiolarians are present throughout the San Francisco de Paula succession w ith the exception of a barren interval in the middle of the section and two thin barren intervals near the top and the base. The most diverse radiolar ian assemblages are from the shaley mudstones, which contain poorly preserv ed radiolarians that range from abundant to very rare. Other lithologies co ntain sparse, poorly preserved assemblages that appear strongly affected by dissolution. Thirty-five lowest and highest occurrences are noted within t he section; however, because of poor preservation, several of these datums are higher or lower than expected when compared with the known global range s of these species. The radiolarians from this study of the San Francisco d e Paula section can be assigned to the stratigraphic interval from the uppe r Paleocene Bekoma campechensis to the lower Eocene Buryella clinata Zones. Species typical of the B. campechensis Zone include Bekoma campechensis, B . demissa, Bekoma spp., Buryella pentadica, B. tetradica, B. foremanae and Lamptonium pennatum. Faunas of the Bekoma bidartensis Zone contain Buryella tetradica, Giraffospyris lata, Phormocyrtis turgida, Podocyrtis (Podocyrti s) papalis, Pterocodon tenellus, Theocorys phyzella, Theocotyle nigriniae, Theocotylissa alpha, T: auctor and Thyrsocyrtis (Thyrsocyrtis) hirsuta. The radiolarian assemblage representing the lower part of the Buryella clinata Zone is similar to that of the Bekoma bidartensis Zone, and also includes the marker species Buryella clinata. Assignment of the upper part of the Sa n Francisco de Paula section to the Buryella clinata Zone is tentative, bec ause of poor preservation. In the San Francisco de Paula section, the preci se location of the Paleocene/Eocene boundary cannot be determined on the ba sis of radiolarians. However, taken together, radiolarian and calcareous na nnofossil evidence indicate that the Paleocene/Eocene boundary is within an unconformity between samples SFP-22 and SFP-21at the highest local occurre nce of Morozovella velascoensis, equivalent to the top of planktonic forami niferal Zone P5. In addition to tabulating the stratigraphic ranges of radiolarian species i n western Cuba, this study presents a preliminary correlation between the l ower Paleogene standard radiolarian low latitude zonation and other zonal s chemes presented for the Caribbean region and mid to high latitudes. Althou gh the San Francisco de Paula section does possess some of the characterist ics desirable in a stratotype for the Paleocene/Eocene boundary, its useful ness in terms of biostratigraphy is limited.