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For those wanting to take a look at the new Gradstein et al. time scale a very nice copy can be downloaded from the ICS website (http://www.stratigraphy.org/) with versions colored up according to either US or European conventions. There are a lot of changes that have been made and, like Martin, I'd be interested in people's perspectives. For example, most of the Cambrian and Ordovician stages now seem to have no names while the traditional names of Silurian stages seem to have all been promoted to Series with new Silurian stage names instituted. I managed to make it to some of the time scale talks at the IGC meeting in Florence last month and it did seem that this time scale was a genuine community effort. We all wait for publication of the CUP book which should answer questions about how this time scale was put together. With respect to the Berggren time scale, I've recently been made aware that CHRONOS project has created a web site for converting between Berggren et al. 1995 and Gradstein et al. 2004 that (I think) bases the conversion on paleomag data. You can access this conversion at the CHRONOS web site (http://services.chronos.org/chiron/chiron/execute?profile=Time%20Scale&module=Convert%20Time). It's a nice implementation. It would be even nicer if conversions like this could be made between other time scales (which, I understand, is one of CHONOS's goals). Norm MacLeod At 11:37 am +0000 13/9/04, Martin Head wrote: >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 >Fax: +44 (0)1223 333392 >Email: mh300@cam.ac.uk >Home page: http://www.geog.cam.ac.uk/people/head -- ___________________________________________________________________ Dr. Norman MacLeod Keeper of Palaeontology The Natural History Museum, Cromwell Road, London, SW7 5BD (0)20-7942-5204 (Office) (0)20-7942-5546 (Fax) http://www.nhm.ac.uk/palaeontology/a&ss/nm/nm.html (Web Page) ___________________________________________________________________
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