Re: Geological timescale

[Phil Bigelow <bigelowp@juno.com>]

"Tim Williams" <twilliams_alpha@hotmail.com> writes:

> Nature 429: 124-125.  Geology: Time lords.
> Gradstein, F. M., Ogg, J. G. &  Smith, A. G. (Eds) A
> Geologic Time Scale 2004, Cambridge Univ.
> Press, (in  press).
> The dates for the beginnings of each period, for the Palaeozoic, 
> Mesozoic, 
> and Cenozoic Eras:

<Snippage>
> ------
> Palaeogene 65.5


That's an important revision for Boundary researchers.  Gradstein et al.
(1995) quote 65.00+/- 0.04 Ma for the K-T Boundary.

K-T boundary rock samples were considered "good" (stratigraphically
accurate) back in 1995.  So are these revisions the result of better
sampling or of better instrumentation or of revisions to the calculations
(or of all three)?



> Neogene 23.03


vs. 23.80 Ma,  Berggren et al. (1995).


Refs.
Gradstein, F.M., F.P. Agterberg, J.G. Ogg, J. Hardenbol, P. Van Veen, J.
Thierry, and Z. Huang. 1995. Mesozoic timescale, pp. 95-126, IN Berggren,
W. A., D.V. Kent, C.C., Swisher, M. Aubry, and J. Hardenbol (eds),
Geochronology, Time Scales and Global Stratigraphic Correlation. SEPM
Special Publication No. 54.


Berggren, W. A., D.V. Kent, C.C. Swisher, and M. Aubry. 1995. A Revised
Cenozoic Geochronology and Chronostratigraphy, pp. 129-212, IN Berggren,
W. A., D.V. Kent, C.C., Swisher, M. Aubry, and J. Hardenbol (eds),
Geochronology, Time Scales and Global Stratigraphic Correlation. SEPM
Special Publication No. 54. 

<pb>
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