paleonet Gradstein et al. 2004 timescale

[Martin Head <mh300@xxxxxxxxxxxxxxxx>]

Folks,

A new time scale was published this year by Gradstein et al. (2004), 
which I guess will replace the two very popular but aging Berggren et 
al. 1995 time scales.  The new Gradstein et al. (2004) time scale is an 
abridgment of a fuller (500 p) account to be published by Cambridge 
University Press later this year (Gradstein et al., in press), but 
Gradstein et al. (2004) already gives a detailed treatment of the 
Neogene, including calibration of planktonic foraminiferal and 
calcareous nannofossil zonations, and dinocyst and radiolarian datums.  
This time scale is therefore ready to test drive, at least for the 
Neogene!

For those of you who have already begun to use Gradstein et al. (2004), 
what is your assessment of it?  I would question some of the dinocyst 
datums, but I am not qualified to judge the handling of the planktonic 
foraminiferal and calcareous nannofossil zonations.  What I do notice 
is that these two zonations have calibrations (to one another and to 
the polarity timescale) that in some cases differ substantially from 
Berggren et al 1995.  For example Zone M3 in the upper Burdigalian is 
1.5 Myr in duration according to Berggren et al. 1995, but only about 
0.1 Myr in Gradstein et al. (2004).  Have the planktonic foram zones 
really changed so much in 9 years?

I assume that some shifts in stage boundaries relative to the polarity 
time scale represent new research on type sections.  I am, however, 
confused by the base of the Burdigalian, as placed in Gradstein et al. 
(2004).  They state that the boundary is close to the top of Chron C6An 
(i.e. top of C6An1n), which is exactly where it is placed in Berggren 
et al. (1995), but the Gradstein et al. chart has the boundary drawn at 
the top of Chron C6An2n.  This seems to represent an internal 
inconsistency of half a million years.  Am I missing something?  I 
wonder if there are other inconsistencies.  Perhaps all becomes clear 
in the full version of the time scale (Gradstein et al. in press).

Finally, how does the new time scale affect the nomenclature of 
sequence boundaries.  I notice, for example, that the sequence boundary 
"Lan 1" is now well into the Burdigalian.

The Gradstein et al. (2004) time scale for the Neogene is clearly an 
improvement on earlier efforts, and is orbitally tuned with an accuracy 
of 40 kyr.  But should we embrace Gradstein et al. (2004) 
unquestioningly?  And I have to ask, is there a new Berggren et al. 
time scale in the pipeline?

Any thoughts most welcome.

Martin

Reference:
Gradstein, F.M., Ogg, J.G., Smith, A. G., Bleeker, W., and Lourens, 
L.J., 2004. A new geologic time scale with special reference to 
Precambrian and Neogene.  Episodes, 27: 83–100.

------------------------------------------------------------------------
Dr Martin J. Head
Department of Geography
University of Cambridge
Downing Place, Cambridge  CB2 3EN
ENGLAND, U.K.

Phone:      +44 (0)1223 339751
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Email:       mh300@cam.ac.uk
Home page:  http://www.geog.cam.ac.uk/people/head