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42705-AC8
Development of an Orbital Calcareous Nannofossil Biochronology for the Paleocene to Lower Oligocene
Nannoplankton populations were decimated by the Cretaceous/Paleocene mass extinction. The Paleocene and Eocene (65-33 Ma) were periods of recovery and diversification following this disaster. In this investigation, the first occurrence (FO) and early abundance increases (AI) of biostratigraphically important taxa are studied in detail to shed light on the ecological changes associated with the origination of a new species. We have investigated the origination of six important taxa during the Paleocene and early Eocene at three sites in the Atlantic, Pacific and Southern Ocean. These sites represent a range of environments including almost 60 degree of latitude. Our analysis includes assemblage counts of samples every two to three thousand years.
The speciation events investigated here show that there was a change in the entire nannofossil assemblage when a new species appeared and increased in abundance. The changes in the environment reflected the preferred environment of the new species, for example, shifting from a cool water, mesotrophic environment to a warm water, oligotrophic environment when a K-mode taxon originated. Multivariate analysis shows that the originating species was highly specialized ecologically. The crossover of Zygrhablithus bijugatus and Fasciculithus spp. During the Paleocene-Eocene thermal maximum (PETM; 55 Ma) was observed in all three locations adding to the global nature of this nannofossil event.
Synchrony in the Paleogene is an unresolved topic in biostratigraphy because until recently there has not been refined orbital records for this time period. One of the key parts of this investigation is the correlation of nannofossil origination events with newly determined orbital records in the deep-sea cores. The first occurrences of the Paleocene taxa were combined with refined orbital records for two of the locations. The first occurrences of Heliolithus kleinpellii and Z. bijugatus are diachronous by approximately 200,000 years between sites. However, the FO of Discoaster multiradiatus and AI of Z. bijugatus are synchronous. The AI of D. multiradiatus is synchronous to within a short (100,000 year) eccentricity cycle.
Finally, we have developed a new and highly resolved time scale for the PETM based on XRF scans of cores from two different locations. This record will allow us to determine rates of environmental change during this abrupt global warming event and compare them to the timing of turnover in the key microplankton and microbenthis groups.
