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Origination and Dispersal of Paragloborotalia Kugleri out of the Indian Ocean at the Oligocene/Miocene Boundary


The first appearance datum (FAD) of Paragloborotalia kugleri, a short-lived but distinct morphospecies of planktic foraminifera, is the biostratigraphic marker used to recognize the Oligocene/Miocene boundary. This FAD has been calibrated to 22.96 Ma (Wade et al. 2011). The Mi-1 event was a globally correlative positive δ18O excursion (~1‰), interpreted to be a short-lived glaciation on Antarctica, that also occurred close to the O/M boundary. Four deep-sea sites from different eras of scientific ocean drilling (DSDP Site 78, ODP Sites 763, 803, IODP 1237) are presented here with new stable isotope records of the Mi-1 event, augmented at each site by finer-scale planktic foraminiferal biostratigraphy, recalibrated paleomagnetic data (Sites 763, 1237), recalibrated chemostratigraphy (803), and astrochronology (bulk density at Site 803 and color reflectance at Site 1237). All datum ages used here are based on astrochonologically-tuned calibrations (forams: Wade et al. 2011; calcareous nannofossils: Backman et al. 2012; radiolarians & additional nannofossils: Expedition 320/321 Scientists, 2010; magnetostratigraphy: Lourens et al. 2004; Pälike et al. 2006), produced for the PEAT Expeditions (IODP Exp. 320/321). In addition, a survey of older DSDP/ODP/IODP shipboard and post-cruise age-models are included in this compilation. The age-models for each site are again updated to the most recent astrochronologically-tuned calibrations. With this compilation it is possible to delineate the origination and spread of P. kugleri from the Indian Ocean into the Pacific Ocean and then the Atlantic Ocean. This suggests the leading edge of the Paragloborotalia pseudokugleri - P. kugleri morphocline is within the Indian Ocean. Here we also provide a recalibration of the P. kugleri datum for the Pacific Ocean, although it is important to point out that the FAD is very reliable in the low to mid-latitudes, relative to the error typically associated with biostratigraphy.