Field of Science

I've Been Waiting For This For A Long Time

Walker, J., & Geissman, J. (2009). 2009 GSA Geologic Time Scale GSA Today, 19 (4) DOI: 10.1130/1052-5173-19.4-5.60

The Geological Society of America has just released its updated geological timescale for 2009 (here and here). A significant revision of this timescale is the Triassic section based on recent studies by Furin et al. (2006) and Kent and Olsen (2008). Most notably is the incorporation of the "long Norian" stage. In the previously published version of the timescale, the Carnian/Norian boundary was dated at 216.5 Ma. Now this boundary is dated at 228 Ma, which in the previous version was the date for the Ladinian/Carnian boundary (Middle/Late Triassic boundary).

The beginning of the Late Triassic is now dated at 235 Ma (previously a strong Middle Triassic date). Incredibly the majority of the Triassic now consists of the Late Triassic. In fact just the Norian stage (24 my) of the Late Triassic is longer than the combined Early (6 my) and the Middle (17 my) Triassic Epochs! The base of the Triassic is still at 251 Ma (defined by a GSSP); however, the age of the Triassic/Jurassic boundary has changed from 199.6 Ma to 201.6 Ma.

As it is now "official" the "long Norian" will have significant implications for the age of the Chinle Formation and other supposed "Carnian" fossil assemblages worldwide as suggested recently by studies such as that of Furin et al. (2006) and Irmis and Mundil (2008). As more GSSPs are established for the Triassic these dates should stabilize.

REFERENCES

Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi: 10.1130/G22967A.1.

Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.

Kent, D.V., and Olsen, P.E.,2008, Early Jurassic magnetostratigraphy and paleolatitudes from the Hartford continental rift basin (eastern North America): Testing for polarity bias and abrupt polar wander in association with the central Atlantic magmatic province: Journal of Geophysical Research, v. 113, B06105, doi: 10.1029/2007JB005407.

No comments:

Post a Comment

Markup Key:
- <b>bold</b> = bold
- <i>italic</i> = italic
- <a href="http://www.fieldofscience.com/">FoS</a> = FoS