GSNZ SIG webinar - PALEOTalk
Refuge or Refuse: reassessing evidence for high survival rates for silica-shelled plankton in the Southern Ocean following the end-Cretaceous mass extinction event, presented by
Dr Chris Hollis, Adjunct Professor, School of Geography, Environment and Earth Sciences, Victoria University of Wellington.
Thirty years ago, I argued that radiolarians and probably diatoms survived the end-Cretaceous mass extinction event. The argument was based on the persistently high abundance of Cretaceous radiolarians in the Paleocene sediments within the Cretaceous-Paleogene (K/Pg) boundary sections of eastern Marlborough. In Marlborough, almost all Cretaceous radiolarian species persisted into the Paleocene for at least 1 million years in most sections and in the primary section studies at Woodside Creek, Cretaceous species remained abundant for 4 million years. High numbers of Cretaceous diatoms had previously been reported from a K/Pg boundary section on Seymour Island, Antarctic Peninsula. Therefore, I posited that high southern latitudes might have acted as a refugia for siliceous plankton during a prolonged impact winter. However, after leading a recent review of radiolarians from other K/Pg boundary records, including the high latitude Indian Ocean, I have to admit that high radiolarian “survival” appears to be restricted to Marlborough. I would now like to suggest that the record of apparent survival might instead be an example of persistent reworking with two processes involved. The argument for reworking is based on the absence of significant numbers of Cretaceous survivors in K/Pg sections in other parts of the world, the lack of any evolutionary diversification within the Cretaceous survivors, and the well-known phenomenon of radiolarian preservation sometimes being unaffected by reworking. I envision the following scenario: (1) Cretaceous radiolarians were deposited on a carbonate ramp extending eastward from central Zealandia along the northern edge of the Chatham Rise; (2) a giant tsunami generated by the K/Pg asteroid impact, dislodged sediments along this ramp resulting in redeposition of Cretaceous radiolarians in earliest Paleocene sediments offshore; (3) within a background of progressive transgression, at least two eustatic falls in sea level caused further erosion along the shallower parts of the ramp, which led to further redeposition of Cretaceous radiolarians.
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Image below is assorted Cretaceous and Paleocene radiolarians from Paleocene Mead Hill Formation, Woodside Creek.
