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Re: Public Database of Geologic Formation Ages?
On Wed, August 24, 2011 3:54 am, Jocelyn Falconnet wrote:
Denver is correct here. "Lower", "Middle", and "Upper" are
chronostratigraphic (rock) units, and biostratigraphic markers are ALSO
technically rock units (bodies of rock whose boundaries are indicated by
presence of index fossils). Biostrat markers are proxies for time, but
they are NOT time units.
The terms "Early" and "Late" are geochronologic (time) units.
So following Denver, the base of the Upper Maastrichtian is the appearance
of H. birkelundi. This event has subsequently been estimated as occurring
at 69.23 Ma.
> Btw, Denver, am I wrong in assuming you meant 'Early' and 'Late' when
> you said 'Lower' and 'Upper' ?
> Le 24/08/2011 00:58, Denver Fowler a Ã©crit :
>> from Fowler (in prep):
>> Lower Maastrichtian:
>> top: 69.23
>> base 70.6 +/- 0.6
>> (Ogg et al, 2004)
>> Lower-Upper Maastrichtian boundary is only informally defined (Ogg et
>> al, 2004),
>> but the definition shown here (Fowler, in prep) is the appearance of H.
>> birkelundi (Landman& Waage, 1993; Cobban, 1993). Alternatives include
>> magnetostratigraphy, exinction of rudist reefs, or inoceramid
>> extinctions (Ogg
>> et al, 2004)
>> Upper Maastrichtian:
>> top: 65.5 +/- 0.3
>> base: 69.23
>> (Ogg et al, 2004)
>> Base of the Upper Maastrichtian (Europe) correlated with the base of the
>> birkelundi zone by Machalski et al (2007).
>> Dodgy enough?
>> Denver Fowler
>> ----- Original Message ----
>> From: "Thomas R. Holtz, Jr."<email@example.com>
>> To: firstname.lastname@example.org
>> Cc: Dinosaur Mailing List<email@example.com>
>> Sent: Tue, 23 August, 2011 16:48:04
>> Subject: Re: Public Database of Geologic Formation Ages?
>> On Tue, August 23, 2011 5:43 pm, Vivian Allen wrote:
>>> To the OP - just round to the nearest Ma? I need some dates for
>>> spreading continuous characters over a phylogeny at the moment, that's
>>> what I'm doing. So Late Maastrichtian would be ~66 Ma. Being more
>>> precise than that seems a bit dodgy - others here seem to agree, but
>>> if anyone has any opinions to the contrary I for one would welcome
>> I would say that you are probably being as precise as possible in nearly
>> all cases. In fact, it can be the case where you can't even tell if you
>> are in the Aptian or Albian, much less a mid-Aptian or late Albian or
>> Thomas R. Holtz, Jr.
>> Email: firstname.lastname@example.org Phone: 301-405-4084
>> Office: Centreville 1216
>> Senior Lecturer, Vertebrate Paleontology
>> Dept. of Geology, University of Maryland
>> Fax: 301-314-9661
>> Faculty Director, Science& Global Change Program, College Park Scholars
>> Fax: 301-314-9843
>> Mailing Address: Thomas R. Holtz, Jr.
>> Department o
>> y of Maryland
>> College Park, MD 20742 USA
Thomas R. Holtz, Jr.
Email: email@example.com Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Faculty Director, Science & Global Change Program, College Park Scholars
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA