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RE: Public Database of Geologic Formation Ages?



> -----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).

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA