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The age of the Daohugou Bed (and the rest of China)



The *Pseudotribos* paper asserts a Middle Jurassic age for the Daohugou Bed and refers to the supplementary information.

The supplementary information, which BTW has 98 pages, contains the following paragraph (p. 3):

"The holotype specimen of CAGS-IG0408-11 was discovered at the Daohugou Locality (N41°18.979', E119°14.318') of Ningcheng County of Inner Mongolia Autonomous Region of People's Repbulic [sic] of China. The fossil is from Bed 3 of the Jiulongshan Formation (sensu Ren et al. 2002). The fossiliferous bed yielding *Pseudotribos* and other fossil vertebrates is 20 meters below the volcanic ash beds dated at 164.2±2.5Ma from feldspar by 40Ar/39Ar dating, and at 164.6±2.4Ma from zircon by SHRIMP 206Pb/238U dating (Chen et al. 2004; Ji et al. 2004; Liu et al. 2006). We follow the field geological interpretation of the Daoguhou site by Liu and Liu (2005; see also Liu et al. 2006) that represents the latest on-site investigation and widely accepted by most workers of this site. Therefore the fossil beds of CAGS-IG0408-11 are approximately 164 ma and is the Middle Jurassic. This age determination is consistent with the biostratigraphical correlation by invertebrates, such as insects (Ren et al. 2002) and conchostracans (Shen et al. 2003), and by fossil plants (personal communication from Prof. Zhi-Yan Zhou)."

Not cited is this paper:

Wang Xiaolin, Zhou Zhonghe, He Huaiyu, Jin Fan, Wang Yuanqing, Zhang Jiangyong, Wang Yuan, Xu Xing & Zhang Fucheng (2005): Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia, Chinese Science Bulletin 50(20), 2369 -- 2376

Abstract:

"Recent fieldwork has extended the distribution of the Daohugou Bed deposits from the Daohugou Village to its several neighboring areas. The fossil-bearing Daohugou deposits uncomformably overlie complex bedrocks, and comprise three major parts. The red shales in the lower part were misidentified as belonging to the Tuchengzi Formation. Field excavation has indicated that the shales of upper part of the bed are the major fossil-bearing horizon. Due to strong tectonic activities, sediments were often folded with the sequences inverted in the region. Some newly recognized con-tacts between the Daohugou Bed and the volcanic rocks showed that the ignimbrite of the Tiaojishan Formation (159--164 Ma) underlies the Daohugou deposits, rather than overlying the latter as previously proposed. Thus, the age of the Daohugou deposits should be younger than the age of the ignimbrite, and thus it was incorrect to correlate the Dao-hugou Bed with the Middle Jurassic Jiulongshan Formation. Although biostratigraphic studies based on conchostracans and insects support a Middle Jurassic-early Late Jurassic age for the Daohugou deposits, vertebrate fossils such as *Liaoxitriton*, *Jeholopterus* and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of *Lycoptera*, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota. We propose that the Daohugou fossil assemblage probably represents the earliest evolutionary stage of the Jehol Biota based on both vertebrate biostratigraphy and the sedimentological and volcanic features which suggest the Daohugou deposit belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group."

The paper has 14 color photos of stratigraphic sections. It can be downloaded for free: http://www.ivpp.ac.cn/pdf/magazine233.pdf.

If you prefer the Chinese version (published in issue 50(19) of the Chinese version of the Chinese Science Bulletin, also in 2005), here it is: http://www.paleomag.net/members/huaiyuhe/publication/05kz2127.pdf.

Furthermore, while the U-Pb dates (164 to 165 Ma ago) are likely in the Middle Jurassic, around the beginning of the Callovian (which began 164.7 +- 4.0 [!] Ma ago), the other date, 159 Ma, is probably not: the Middle-Late Jurassic boundary is dated to 161.2 +- 4.0 Ma ago, and the Oxfordian-Kimmeridgian boundary to 155.7 +- 4.0 Ma ago. http://www.stratigraphy.org/gssp.htm

Insects and conchostracans don't seem to give very precise dates. Remember that both were used to put the Yixian Fm into the Jurassic.

In sum, because it overlies the Jiulongshan Fm and is older than the Yixian Fm, the Daohugou Bed can be Late Jurassic, Berriasian, Valanginian, Hauterivian, or even Barremian in age.

Its relationship to the Dabeigou Fm, which is Hauterivian (ref below), stays unknown; both lack *Lycoptera*, which is present in the Yixian and Jiufotang Fms.

He H. Y., Wang X. L., Jin F., Zhou Z. H., Wang F., Yang L. K., Ding X., A. Boven & Zhu R. X.: The ^40Ar/^39Ar dating of the early Jehol biota from Fengning, Hebei province, northern China, Geochemistry, Geophysics, Geosystems 7(4), pages "1 of 8" to "8 of 8", 12 April 2006
http://www.paleomag.net/members/huaiyuhe/publication/JCG.pdf


Incidentally, the Lujiatun Bed of the Yixian Fm is no older than the Jianshangou Bed of the same formation -- 123.2 +- 1.0 Ma:

He H. Y., Wang X. L., Zhou Z. H., Jin F., Wang F., Yang L. K., Ding X., A. Boven & Zhu R. X.: ^40Ar/^39Ar dating of [the] Lujiatun Bed (Jehol Group) in Liaoning, northeastern China, Geophysical Research Letters 33(L04303), pages "1 of 4" to "4 of 4", 24 February 2006
http://www.paleomag.net/members/huaiyuhe/publication/2005GL025274.pdf


That is not Hauterivian and not Barremian, but _Aptian_. The Barremian-Aptian boundary was 125.0 +-1.0 Ma ago. http://www.stratigraphy.org/gssp.htm

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And by the way... have a look here... http://www.ivpp.ac.cn/pdf/
Not that there was any danger, but I shall never get bored again.