Abundance and diversity changes among calcareous nannofossil assemblages across the early/late Oligocene boundary in the paleo-equatorial Pacific Ocean
(English)Manuscript (Other (popular science, discussion, etc.))
Ocean Drilling Program (ODP) Leg 199 recovered a complete Oligocene sediment sequence at Site 1218 in the paleo-equatorial Pacific Ocean. This paper presents a high-resolution study of relative abundances and diversity fluctuations of calcareous nannofossil assemblages in an Oligocene interval showing high carbonate contents. The data generated are compared with stable isotope (C, O) and sediment flux data in order establish possible relationships to changes in sea surface temperature and productivity. The nannofossil assemblage is dominated by Cyclicargolithus floridanus, Sphenolithus moriformis and Coccolithus pelagicus, which show a combined mean abundance of 84 % throughout the investigated 3.6 Myr interval (30.0 - 26.4 Ma). All component taxa show fluctuations in abundance. Variations in abundance and Shannon diversity index have been used to subdivide the 3.6 Myr long study interval into four subintervals. Intervals of highest Shannon index diversity coincide with Oi-glaciation events. However, the variations in abundance of selected nannofossil taxa do not appear to correlate with changes in either oxygen isotopes or carbon isotopes. This presumably indicates that a dynamic equilibrium did not exist between these Oligocene calcareous nannoplankton assemblages and changes in surface water temperature or productivity conditions. Observed changes in the nannofossil assemblages thus could have probably been driven by other factors, like for example, the internal evolutionary dynamics within the coccolithophore communities.
calcareous nannofossil, mid-Oligocene, Shannon diversity index, Site 1218, paleo-equatorial Pacific Ocean
Research subject Geology
IdentifiersURN: urn:nbn:se:su:diva-27599OAI: oai:DiVA.org:su-27599DiVA: diva2:216402