Ocean Drilling Program Site 926 sediments are well suited to serve as a reference section for calcareous nannofossil biostratigraphy from the low-latitude Atlantic Ocean in the 0- to 14-Ma time interval. Reasons include completeness in deposition and recovery, superbly resolved orbitally tuned chronologic control, generally good carbonate preservation, and the fact that this site represents a location where much evolution evidently occurred. Thirty-four nannofossil events, from the top of Ceratolithus acutus to the top of Sphenolithus heteromorphus, have been investigated at 10-cm sample resolution (averaging 6 k.y.) in over 1400 samples from the earliest Pliocene (5.046 Ma) to the middle Miocene (13.523 Ma). These 34 events have been determined with an average chronological precision of ±7 k.y.
This study emphasizes (1) the importance of quantitative approaches to determine time-dependent abundance variation of species to improve the understanding of paleoecologic responses of biostratigraphically useful species to variable and changing paleoenvironmental conditions; and (2) the importance of determining the smallest meaningful sampling interval to capture the finest details of the records of evolutionary emergence or extinction of species that are preserved in cores.
1Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), 1997. Proc. ODP, Sci. Results, 154: College Station, TX (Ocean Drilling Program).
2Department of Geology and Geochemistry, Stockholm University, S-106 91 Stockholm, Sweden. jbackman@geo.su.se backman@geo.su.se
3Facoltá di Scienze MM.FF.NN., Universitá “G. d’Annuzio,” Campus Universitario Madonna della Piane, Via dei Vestini 31, I-66013 Chieti Scalo, Italy. raffi@unich.it
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