[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Public Database of Geologic Formation Ages?

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

On the biology/geology front, palaeontology now encompasses a lot of
highly specialised disciplines. No-one is going to be world-class at
all of them. This is a natural progression of the field, far as I see
it. From my perspective (anatomy and biomechanics), learning,
acquiring and applying data and techniques from neontological and
mechanical studies takes up so much time and brain-space that the
geology of the specimens (although I do have a degree in geology) I
work on is something I will happily leave to someone else.

> On 23 August 2011 21:16, Jaime Headden <qi_leong@hotmail.com> wrote:
>> Not always enough of them. Comparative anatomy isn't even trained in MODERN 
>> paleontological students to the degree it used to be. The cross-discipline 
>> position now is a smattering of both geo and bio, without the emphasis on 
>> the principles of either to get the researcher comprehensive _enough_ in 
>> both to be an earnest researcher in both. Nor should he. We can't all be 
>> polymaths. That's why you get people who know some crud about the 
>> disciplines you are not too comprehensive on (as Tom said), and maybe they 
>> should just be coauthors rather than just editors -- I know, don't want to 
>> share the limelight and the stage.
>> Cheers,
>>  Jaime A. Headden
>>  The Bite Stuff (site v2)
>>  http://qilong.wordpress.com/
>> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>> "Ever since man first left his cave and met a stranger with a
>> different language and a new way of looking at things, the human race
>> has had a dream: to kill him, so we don't have to learn his language or
>> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
>> Backs)
>> ----------------------------------------
>>> Date: Tue, 23 Aug 2011 14:18:59 +0100
>>> From: mike@indexdata.com
>>> To: tholtz@umd.edu
>>> CC: saint_abyssal@yahoo.com; dinosaur@usc.edu
>>> Subject: Re: Public Database of Geologic Formation Ages?
>>> On 23 August 2011 14:01, Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:
>>> >> -----Original Message-----
>>> >> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]
>>> >> On Behalf Of Saint Abyssal
>>> >> Sent: Monday, August 22, 2011 11:03 PM
>>> >> To: Dinosaur Mailing List
>>> >> Subject: Public Database of Geologic Formation Ages?
>>> >>
>>> >> I'm having a surprising amount of trouble finding precise
>>> >> ages for geologic formations. Is there a public database
>>> >> available with the ages of a significant number of
>>> >> stratigraphic units? I'm creating timelines for Wikipedia
>>> >> showing the duration of times represented by different units
>>> >> but having to hunt down ages for each one is exhausting.
>>> >> Worse, I'm having trouble finding exact numbers for many
>>> >> units. I understand the gist of say, "late Maastrichtian" but
>>> >> I need exact numbers to enter into the timeline template and
>>> >> to enter guesstimates as to what exact numbers the authors
>>> >> meant by this would violate Wikipedia's policy forbidding
>>> >> original research.
>>> >>
>>> >
>>> > There are some regional ones, such as for Australia
>>> > (http://www.ga.gov.au/products-services/data-applications/reference-databases/stratigraphic-units.html)
>>> >  or the US
>>> > (http://ngmdb.usgs.gov/Geolex/geolex_qs.html).
>>> >
>>> > However, several things to keep in mind:
>>> > 1) Formations and other lithostratigraphic units are NOT time units and 
>>> > their boundaries are NOT time boundaries: that is, the
>>> > boundary between Formation X and overlying Formation Y can be one age at 
>>> > one location, but a different age at other ones.
>>> > Formational boundaries represent changes of depositional environment, not 
>>> > depositional time. Classic example: the boundary between
>>> > the lower (nearshore sand deposits) Tapeats Sandstone and the upper 
>>> > (offshore mudbank) Bright Angel Shale happened during the Early
>>> > Cambrian in the western part of the Colorado Plateau, but during the 
>>> > Middle Cambrian further East. The formational boundaries shift
>>> > throughout time: they are diachronous or "time transgressive".
>>> >
>>> > 2) As David pointed out, the vast majority of units do not have 
>>> > radiometric dates, and they age is determined by interpolation
>>> > between datable units and by biostratigraphic, magnetostratigraphic, or 
>>> > other means.
>>> >
>>> > In other words, DON'T PUT IN NUMBERS when you don't have justification 
>>> > for them! That is unscientific. Use the units that the
>>> > geologists use: that is the reason we use geochronologic terms like "late 
>>> > Maastrichtian": they are accurate if not precise.
>>> >
>>> > Also makes sure that you get the aid of someone who has studied 
>>> > stratigraphy to do the editing of the stratigraphic entries.
>>> >
>>> > (Just want to add that there are a lot of even professional 
>>> > paleontologists--more today than in the past, actually--who actually are
>>> > lacking in basic knowledge of historical geological disciplines. This is 
>>> > what comes from the field shifting to being predominently a
>>> > biological one rather than a shared geological-biological one).
>>> On the positive side, a lot more palaeontologists understand anatomy now!
>>> -- Mike.