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Giantism in Oligocene planktonic foraminifera Paragloborotalia opima: Morphometric constraints from the equatorial Pacific Ocean

Wade, BS; Poole, CR; Boyd, J; (2016) Giantism in Oligocene planktonic foraminifera Paragloborotalia opima: Morphometric constraints from the equatorial Pacific Ocean. Newsletters on Stratigraphy , 49 (3) pp. 421-444. 10.1127/nos/2016/0270. Green open access

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Abstract

The extinction of Oligocene planktonic foraminifera Paragloborotalia opima is an important biostratigraphic marker for the upper Oligocene (base Zone O6 [P22]), however the taxonomy of the morphospecies is unclear and therefore its biostratigraphic use is compromised. We conducted morphometric and scanning electron microscope analyses on the Paragloborotalia opima-nana plexus and investigated whether the two morphospecies P. opima (Bolli) and P. nana (Bolli) could be quantitatively separated or formed a continuous morphocline. These two morphospecies have previously been classified by their diameter, with P. opima defined as the larger morphospecies (0.39–0.55 mm) and P. nana confined to 0.32 mm. The problem with this classification is that many specimens fall between 0.32 and 0.39 mm. We measured the maximum size of 1215 specimens of Paragloborotalia from equatorial Pacific Ocean Integrated Ocean Drilling Program Site U1334, corresponding to planktonic foraminiferal Biozones O6–O2 and Chrons C8r to C11r (26.3 to 30.8 Ma). We found that the number of chambers and shape outline could not be used to determine these two morphotypes of Paragloborotalia, but size is a suitable delimiting character. We therefore reassess the taxonomy of the opima-nana plexus. Our data confirm that the 'transition' forms are consistent with P. opima and that the 0.32 mm criterion is valid for the identification of P. nana. Through the studied interval the maximum size of P. opima increases from 0.44 mm to 0.68 mm, with the largest specimens in the upper Oligocene in the lower part of Chron C9n. We propose that the progressive giantism of P. opima through the mid-late Oligocene in the equatorial Pacific Ocean is in response to high productivity.

Type: Article
Title: Giantism in Oligocene planktonic foraminifera Paragloborotalia opima: Morphometric constraints from the equatorial Pacific Ocean
Open access status: An open access version is available from UCL Discovery
DOI: 10.1127/nos/2016/0270
Publisher version: http://dx.doi.org/10.1127/nos/2016/0270
Language: English
Additional information: Copyright © 2016 The authors. Open Access article made available under the Creative Commons Attribution-NonCommercial 3.0 Unported (CC BY-NC 3.0) licence (https://creativecommons.org/licenses/by-nc/3.0/)
Keywords: Planktonic foraminifera, morphometrics, taxonomy, size, giantism, extinction
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1485757
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