GSA Connects 2021 in Portland, Oregon

Paper No. 38-5
Presentation Time: 2:45 PM


RAFFI, Isabella, PhD h c, Department of Engineering and Geology, Universita' "G. d'Annunzio" di Chieti-Pescara, Campus Universitario - via dei Vestini 31, Chieti Scalo, 66013, Italy and WADE, Bridget, Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, United Kingdom

Calcareous microfossils (nannoplankton and planktonic foraminifers) benefit from a rich fossil record as the dominant sediment-forming oceanic groups. They thus provide valuable records of the biotic response of marine plankton to climate evolution in the Miocene. The timing of evolution and extinction events are well constrained in the tropical and subtropical oceans due to the extensive archives of ocean drilling, the establishment an astronomical chronology and the application of these groups for biostratigraphy (Raffi et al., 2020). Their distribution and evolutionary patterns roughly but distinctively outline the development of paleo-environmental conditions in the Miocene. A comparison between the patterns observed in calcareous nannofossils and planktonic foraminifera assemblages reveals a similar mutual response to climatic/environmental evolution is evident at the large scale. As an example, a remarkable turnover in nannofossil assemblages is recorded within the middle and late Miocene (17-10 Ma), and straddles parts of the critical intervals of the Miocene Climatic Optimum (MCO) and Middle Miocene Climatic Transition (MMCT). This turnover involves the main taxonomic groups, as discoasterids and reticulofenestrids, which with a stepwise pattern redesign the nannofossil assemblages. Extinction rates in planktonic fora­minifers increase abruptly around the MMCT and remain high until 9.5 Ma. The latest Miocene is a time of diversification in planktonic foraminifers with the evolution of many morphospecies within the globorotaliids. The enhanced extinction in both calcareous nannofossils and planktonic foraminifers at the MMCT suggests that both phytoplankton and zooplankton responded negatively to climatic deterioration. Deeper dwelling thermocline planktonic foraminifer taxa were the drivers of increased diversity in the late Miocene. Here we present the integrated patterns of calcareous plankton evolution in the Miocene and discuss the relationship with climatic records during this dynamic time interval.


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