When I read some articles, I found the time was not consistent to the geological time scale. For example, In the Article Archaefructaceae, a new basal angiosperm family ( Sun G, 2002), the fossil was inferred 124.6 mya, and arttributed to upper Jurassic of China. I checked the geological time scale, the Jurassic was between 201.3 mya and 152.1 mya and Cretaceous began 145 mya. How to explain this？
In the article by Sun (2002), they had a small note stating the following:
(9) The age of the Yixian Formation of western Liaoning, China, is uncertain. We allow for a range from 145 to 125 million years, which corresponds with the Upper Jurassic to Lower Cretaceous (12, 31, 38–45).
Therefore, at that time, they didn't know whether it was Late Jurassic or Early Cretaceous in age. Be aware that since then, there has been new radiometric datings for the Yixian Formation in China showing that it was actually Early Cretaceous in age:
http://link.springer.com/article/10.1360/02tb9031#page-1
http://www.sciencedirect.com/science/article/pii/S0031018213002502
There is a review of all radiometric datings for this Formation in Wu et al. (2013), Palaeo3 and even an astronomical calibration so it appears that this Formation is now very well dated.
Thinks to all of you. The answers made me understand the question well. I can say the inferred time of the fossils is more accurate and gives us more important information, as the accurate years of historical events are more meaningful than the historical stages. Yet, I still cannot understand the scale of the geological time scale variation would reach to that extend.
Hi Mark,
it is a science forum, not a deep time adherent/doctrine/dogma forum, or a popularity context, you are entitled to your currently still popular opinions but repetition over and over does not make them facts :)
so to be a good scientist try and keep an open mind and do not get worked up when someone has an alternate view.
Xie, is it really so surprising ? As far as I can read on the Yixian Fm., it's mostly continental siliciclastic sediments trapped between basalts so it's no surprise that it was difficult to date with precision for a long time. Continental sediments are always more difficult to date with precision with fossils because, contrary to the marine sediments, the fossils contained in continental sediments have a much more limited geographical extent and their biostratigraphy is thus much more imprecise than marine groups. In the original article of 2002, an uncertainty of 20 Myr across the Jurassic/Cretaceous boundary is thus not so shocking. But of course, it's great that it's now much better constrained to Barremian-Aptian through the recent radiometric datings at 121 to 125 Myr.
The wikipedia webpage on the Yixian Fm. is quite informative:
https://en.wikipedia.org/wiki/Yixian_Formation
Dear Nicolas, thank you for giving me much more information. I major in sysematics, but I didn,t learn biostratigraphy systematically. I would read more papers about the question.
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