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Calcidiscus tropicus
Edited by Jeremy Young on Wed, 09/03/2011 - 15:48
Calcidiscus tropicus Kamptner, 1956 sensu Gartner, 1992
Description: Species of Calcidiscus producing circular coccoliths with open central-area, 7-10μm.
Remarks: Not always separated from C. leptoporus. Miocene forms often have a bicyclic proximal shield, in Pliocene forms a coarse grill is often visible in central opening. Larger forms (>10µm) are separated as C. macintyrei, possibly evolves into C. quadriperforatus.
Original description:
Variants;
- C. leptoporus ssp centrovalis (Stradner and Fuchs, 1980) Perch-Nielsen, 1984 - similar to C. tropicus but sub-circular;
- C. carlae (Lehotayova and Priewalder, 1978) Janin, 1992 [Cycloperfolithus] - Paratethyan form, with fine grill in central-area, and bicyclic proximal shield.
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Neogene: Calcidiscus tropicus
Comments
C.carlae as a marker in the Pliocene
In the Gulf of Mexico the LAD of C. carlae (the type with a fine grill in the central area) is used as a marker equivalent in age to the LAD of Discoaster tamalis or slightly younger, depends on who you talk to. If you talk to me, they are equivalent. I found the same co-occurence of these two taxa in the South Pacific in the material from ODP leg 135.
The grill is often difficult to discern without the use of phase contrast.
C. carlae and C. tropicus
Two comments:
(1) C. carlae appears to be a valid species, as both its overall range (NN9? to NN16) and abundance patterns (prominent increases in basal NN16/uppermost NN15 and within NN11) are distinct from similar forms, and I have never seen anything that I would have called a C. macintyrei or C. tropicus that had a grill.
(2) C. tropicus itself may be a catchall form. There is a very distinct form with a very large central opening and high collar that ranges from NN5/6 to NN11 (see the photo of the specimen labeled 4-16tropicus for a good example) that makes a useful marker within NN11.