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

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.