EGU2020-2396
https://doi.org/10.5194/egusphere-egu2020-2396
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Morphological evolution of menardiform globorotalids at ODP Hole 806C (Ontong-Java Plateau)

Michael Knappertsbusch
Michael Knappertsbusch
  • Natural History Museum Basel, Earth Sciences, Basel, Switzerland (michael.knappertsbusch@unibas.ch)

The morphological evolution was investigated in the tropical Neogene planktonic foraminiferal lineage Globorotalia menardii, G. limbata and G. multicamerata during the past 8 million years at ODP Hole 806C (Ontong-Java Plateau). This research is an extension of previous studies from the Caribbean Sea, the tropical Atlantic and the Eastern Equatorial Pacific.

The peripheral influence of Agulhas Current faunal leakage of Indian Ocean or even Pacific menardiforms into the South Atlantic is suspected to be responsible for a transgressive, transatlantic expansion of large menardiforms from 2.3-2.06 Ma to 2.58-1.7 Ma, which installed after a Northern Hemisphere Glaciation (NHG) size incursion of menardiforms around 2.6 Ma (Knappertsbusch, 2007 and 2016; Knappertsbusch & Friesenhagen 2018). The investigation from Western Pacific Warm Pool (WPWP) ODP Hole 806C, i.e. from an area outside reach of Agulhas Current, serves as a blind test for this szenario. Here, stable warm environments prevailed back to Pliocene times, and influences of NHG are expected to bear less severely on shell size evolution than in the Atlantic Ocean.

For this study >5250 specimens comprising G. menardii, G. limbata and G. multicamerata from 33 stratigraphic levels were morphometrically investigated using imaging- and microfossil orientation robot AMOR. Attention was given to trends of spiral height (δX) versus axial length (δY) in keel view, for which bivariate contour- and volume density diagrams were constructed for visualization of evolutionary patterns.

In WPWP Hole 806C G. menardii evolved in a more gradual manner than in the Atlantic. Plots of δX versus δY reveal bimodality between 3.18 Ma – 2.55 Ma with a dominant mode of smaller G. menardii (δX<~300 μm) persisting until the Late Quaternary, and a weak mode of larger G. menardii (δX>~300 μm) until 2.63 Ma. Up-section, bimodality vanished but G. menardii populations shifted towards extra large shells between 2.19-1.95 Ma supporting the possibility of long-distance diversal in this group. Morphological evolution of G. limbata and its evolutionary successor G. multicamerata in the WPWP are also different from those in the tropical Atlantic, but analyses need still further investigation.

In summary, Pacific menardiform globorotalid patterns contrast those in the Atlantic realm. There is inter-oceanic morphological asymmetry with considerable regional environmental control over shell evolution and indication of long-distance dispersal of G. menardii, both with implications for biostratigraphic applications.

 

References

Knappertsbusch, M. and Friesenhagen, T. (2018). Prospecting patterns of morphological evolution in menardiform globorotalids along Agulhas‘ trackway: Review and research in progress. Abstract. FORAMS 2018 Symposium, 17-22 June 2018, Edinburgh, UK., Session IX, temporary abstracts, 331.

Knappertsbusch, M. (2016). Evolutionary prospection in the Neogene planktic foraminifer Globorotalia menardii and related forms from ODP Hole 925B (Ceara Rise, western tropical Atlantic): evidence for gradual evolution superimposed by long distance dispersal ? Swiss Journal of Palaeontology, 135, 205-248.

Knappertsbusch, M. (2007). Morphological variability of Globorotalia menardii (planktonic foraminifera) in two DSDP cores from the Caribbean Sea and the Eastern Equatorial Pacific. Carnets de Géologie / Notebooks on Geology, Brest, Article 2007/04. http://paleopolis.rediris.es/cg/CG2007_A04/index.html.

More info: https://micropal-basel.unibas.ch/

How to cite: Knappertsbusch, M.: Morphological evolution of menardiform globorotalids at ODP Hole 806C (Ontong-Java Plateau), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2396, https://doi.org/10.5194/egusphere-egu2020-2396, 2020

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Presentation version 3 – uploaded on 29 Apr 2020
Comment added for reading interactive VDD in section 4.
  • CC1: Comment on EGU2020-2396, Chris Brierley, 04 May 2020

    Hello Michael,

    I was very impressed with the inclusion of a 3D image into the poster. I didn't even know this could be done.

    I was wondering why you didn't try to collapse the dimensions of your dataset down. Fundamentally the vast majority of the variance lies on the y=~2x line. You may get more useful findings by plotting a length variable and a deviation from a 2:1 ratio.

    Chris

    • AC1: Reply to CC1, Michael Knappertsbusch, 04 May 2020

      Dear Chris

      >Hello Michael,

      >I was very impressed with the inclusion of a 3D image into the poster. I didn't even know this could be done.

      > I was wondering why you didn't try to collapse the dimensions of your dataset down. Fundamentally the vast majority of the variance lies on the y=~2x line. You may get more useful findings by plotting a length variable and a deviation from a 2:1 ratio.

      Chris

      Thanks for commenting.

      True, I could look perpendicular to the DY axis (spiral height) to see most of the variation. Actually the VDD representation and its rotated version (with the 45° plane parallel to the computer screen) is nothing more than a bivariate principal components analysis.

      For me, as person looking down the microscope was always important to understand the practical meaning of each variable and their linear combinations. Where can I see variation and separation of possible clusters best ? That's too often not at all easy to understand in classical PCA's using characters. It could be, for example that the 1:2 raio (slope of the scatter diagrams) rotate a bit through time, due to evolution/adaptation. Then an "all over" PCA analysis becomes very difficult to interprete (you'd have to look into time-steps with changing slopes).  Just imagine, if you only look at DX (spiral height): You'd rarely see any bi-or multimodality to develop. In DY direction you do. And in the 45° you do even better. And just adding one or more dimensions more makes it really difficult to understand in terms of taxonomic separation. In the present case with G. menardii I do not have that problem because ontogenetic shell size development in the DX DY diagram is somewhat linear and more-or less in the same direction. But I had other cases in coccolithophores (Knappertsbusch 2000, J. Paleontology) where this was a different cas.

      Kind regards

      Michael

Presentation version 2 – uploaded on 28 Apr 2020 , no comments
Numbering of sections corrected. Interactive VDD embedded in section 4.
Presentation version 1 – uploaded on 14 Apr 2020 , no comments