Coccolithus miopelagicus


Ancestry: Coccolithophores -> Coccolithales -> Coccolithaceae -> Coccolithus -> C. pelagicus group -> Coccolithus miopelagicus
Sister taxa: C. crassus, C. hulliae, C. pelagicus, C. eopelagicus, C. miopelagicus, C. latus, C. bownii, C. tenuiforatus,

Short diagnosis: Coccoliths very large, 14-20µm, usually 15-17µm, no bar in central area.


Taxonomy:

Citation: Coccolithus miopelagicus Bukry, 1971
Rank: Species
Notes & discussion: Central area is smaller releative to coccolith size than in typical C. pelagicus (see original description and comments)

Farinacci & Howe catalog pages: Coccolithus miopelagicus + *

Short diagnosis: Coccoliths very large, 14-20µm, usually 15-17µm, no bar in central area.

Geological Range:
Notes: The species has often been recorded in sediments of age NP24 to NN4 (e.g. Neptune database records) but these are probably not the distinctive very large specimens with a wide rim.
Last occurrence (top): within NN8 zone (10.55-10.89Ma, top in Tortonian stage). Data source: Young 1998
First occurrence (base): within NN5 zone (13.53-14.91Ma, base in Langhian stage). Data source: Young 1998

Plot of occurrence data:

References:

Bukry, D., (1971). Cenozoic calcareous nannofossils from the Pacific Ocean. San Diego Society of Natural History Transactions, 16: 303-327.

Young, J.R., (1998). Neogene. In: Bown, P.R. (Editor), Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publications Series. Chapman & Hall, London, pp. 225-265.


Nannotax3 - Coccolithophores - Coccolithus miopelagicus by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-4-2017

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Mike Styzen (Noble Energy, US)
Splitting C. pelagicus: The extinction of this species can be a good Miocene marker, but lower range of this species is problematic. Most of the other Neogene workers I've spoken with agree. Below NN4 you continue to periodically see pulses of very large C. pelagicus in this size range (> 13or 14 µm) all the way down into the Oligocene. Eventually, working down section, you start seeing specimens on the order of 20 µm and if you are paying attention, they can be called C. eopelagicus.

This isn't very scientific, but it is what happens. There are some workers who distinguish this species on something other than size. They tend not to measure, or sometimes call smaller specimens something like ?C. miopelagicus small? At that point the upper range also becomes a problem. My split on the pelagicus group works like this:
  • < 10µm = C. pelagicus 
  • 10 µm - 13 µm = C. cf. miopelagicus 
  • 13 µm - ~20 µm = C. miopelagicus 
  • ~20+ µm and Oligocene or older = C. eopelagicus 
Notice that the only real age caveat is for C. eopelagicus. For the rest I call them whatever age they are. I encourage contractors who do work for me to use this system as well (some just can?t bring themselves to do it). I understand that this is a very industrial approach, and that it is probably not strictly to code, but it avoids confusion. I know others I know others have had a pretty hard look at this group and I hope they see fit to comment here!
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Jeremy Young (NHM, UK)
Interesting point - the C. pelagicus lineage is certainly a fine target for a detailed study. However, as far C. miopelagicus goes I think the original description is correct in saying that C. miopelagicus has a smaller central area (cal= 0.5 x dsl) than C. eopelagicus of similar size (cal = 0.6 x dsl). I also find C. miopelagicus has flatter shields, this is readily observable in light microscope because you can get more of the specimen in focus. My hunch has been that C. miopelagicus evolved from regular size C. pelagicus in the middle Miocene and is not directly related to the large Oligocene forms (C. eopelagicus).
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Mike Styzen (Noble Energy, US)
You are most probably right about the features described in the original description. Unfortunately, for biostratigraphic purposes, the C. miopelagicus LAD datum works better when combined with the size criteria. Generally from what I've seen, once they get as large as 10 µm they just about all exhibit those features. Those smaller forms, however, trickle up section and tend to make the marker more diachronous. That's why I use the cf category above. It's a pertty good flag to watch for the larger specimens, but not a good top over wide areas. I haven't really paid attention to the morphology lower down in the Miocene, so I can't comment on that. I know that things with the general morphology of C. pelagicus appear to continue right down into the Eocene.
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Steve Starkie (Ichron, UK)
I totally agree with you Mike. There is definitely a precursor top C. miopelagicus as you suggest C. cf. miopelagicus. I find it trickles up into NN9/10. I also use, I guess like most workers, the big size shift as a separate event.
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