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      Pleistocene Calcareous Nannofossil Biostratigraphy and Gephyrocapsid Occurrence in Site U1431D, IODP 349, South China Sea

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      Geosciences
      MDPI AG

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          Abstract

          We reinvestigated the Pleistocene calcareous nannofossil biostratigraphy of Site U1431D (International Ocean Discovery Program (IODP) Expedition 349) in the South China Sea (SCS). Twelve calcareous nannofossil Pleistocene datums are identified in the site. The analysis confirms that the last occurrence (LO) of Calcidiscus macintyrei is below the first occurrence (FO) of large Gephyrocapsa spp. (>5.5 μm). The FO of medium Gephyrocapsa spp. (4–5.5 μm) is also identified in the samples through morphometric measurements, which was unreported in shipboard results. Magnetobiochronologic calibrations of the numerical ages of LO of Pseudoemiliania lacunosa and FO of Emiliania huxleyi are underestimated and need reassessment. Other potential markers such as a morphological turnover of circular to elliptical variants of Pseudoemiliania lacunosa and a small Gephyrocapsa acme almost synchronous with the FO of Emiliania huxleyi may offer biostratigraphic significance in the SCS. The morphologic changes in Gephyrocapsa coccoliths are also examined for the first time in Site U1431D. Placolith length and bridge angle changes are comparable with other ocean basins, suggesting that morphologic changes are most likely evolutionary novelties rather than being caused by local climate anomalies.

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          Most cited references46

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          A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

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            An alternative astronomical calibration of the lower Pleistocene timescale based on ODP Site 677

            Ocean Drilling Program (ODP) Site 677 provided excellent material for high resolution stable isotope analysis of both benthonic and planktonic foraminifera through the entire Pleistocene and upper Pliocene. The oxygen isotope record is readily correlated with the SPECMAP stack (Imbrieet al.1984) and with the record from DSDP 607 (Ruddimanet al.1986) but a significantly better match with orbital models is obtained by departing from the timescale proposed by these authors below Stage 16 (620 000 years). It is the stronger contribution from the precession signal in the record from ODP Site 677 that provides the basis for the revised timescale. Our proposed modification to the timescale would imply that the currently adopted radiometric dates for the Matuyama–Brunhes boundary, the Jaramillo and Olduvai Subchrons and the Gauss–Matuyama boundary underestimate their true astronomical ages by between 5 and 7%.
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              A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years☆

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                Author and article information

                Journal
                GBSEDA
                Geosciences
                Geosciences
                MDPI AG
                2076-3263
                October 2020
                September 28 2020
                : 10
                : 10
                : 388
                Article
                10.3390/geosciences10100388
                bf3a29de-9523-4c7f-a0cd-0ed246f6762a
                © 2020

                https://creativecommons.org/licenses/by/4.0/

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