Recent, as yet unpublished work correlating Letter Stages with planktonic zones and isotopic ages shows the "T.c" Letter Stage to have been a short period within the basal Oligocene (c. 34 to 32 mybp).
The images shown here are reduced to about 1/5 their original resolution and highly compressed as JPG files. Original images available on request, as TIF files from 120 to 600 MB in size
- Basal Oligocene Limestone (316 KB). From the unpublished site at Cikalong West Java. A second, much broader view of the same thin section is here but is 1.2 MB in size.
- Basal Oligocene heterostegines (216 KB). From Tan Sin Hok's site at Cimanggu, West Java. Abundant Planostegina is in the marl immediately above this limestone, and is present as 2 out of 3 two specimens here, one with an umbonal thickening P. praecursor on the right of the image. The large specimen on the left is "Heterostegina cf. depressa" of Tan, found at this location. This is a "maturo-evolute" test and therefore questions the validity of Banner & Hodgkinson's division of the Heterostegies into H. (Vlerkina) and H. (Heterostegina) on the presence of this test style in the latter - which is a younger Neogene lineage. "Heterostegina cf. depressa" Tan appears to grade into the more involute H. (Vlerkina) - see images in T.d and basal T.e sections, which then grades into Tansinhokella at the base of Letter Stage T.e2-3.
