Sedimentary sequences obtained from drilling during Integrated Ocean Drilling Program (IODP) Expedition 320/321, “Pacific Equatorial Age Transect (PEAT)” at eight sites (Sites U1331–1338) in the equatorial Pacific offer an ideal record for reconstructing the evolution of the ocean/climate system throughout the Cenozoic. The sediments drilled at Site U1335 record short-term events of paleoceanographic significance, including the early Miocene climatic optimum (MCO) and the middle Miocene climatic transition (MMCT). Abundant well preserved radiolarians were recovered from the lower Miocene radiolarian Zone RN2 through middle Miocene Zone RN5 at IODP Site U1335. A total of 46 radiolarian datum levels consisting of 20 first occurrences (FOs), 25 last occurrences (LOs), and one evolutionary transition (ET) was recognized within the studied interval at Site U1335. Of these datum levels, 36 radiolarian datum levels were directly tied to the geomagnetic polarity time scale (GPTS) across the early/middle Miocene boundary. The general magnitude of evolutionary change was estimated based on the total turnover rate (the sum of FOs and LOs per 0.5 m.y.) of tropical radiolarians, and two minor faunal turnovers of radiolarian species were recognized between 16.5 and 14.7 Ma and between 13.9 and 13.4 Ma. These faunal turnovers were associated with regional environmental changes such as the increased biological productivity in the equatorial Pacific during the MCO and the MMCT.
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1 October 2019
Radiolarian Biostratigraphy and Faunal Turnover across the Early/Middle Miocene Boundary in the Equatorial Pacific
Shin-Ichi Kamikuri,
Theodore C. Moore,
Hiroki Matsui,
Hiroshi Nishi
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Paleontological Research
Vol. 23 • No. 4
October 2019
Vol. 23 • No. 4
October 2019
biological productivity
early Miocene climatic optimum (MCO)
geomagnetic polarity time scale (GPTS)
middle Miocene climatic transition (MMCT)
total turnover rate