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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
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
"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:
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.
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
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
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
That is not Hauterivian and not Barremian, but _Aptian_. The
Barremian-Aptian boundary was 125.0 +-1.0 Ma ago.
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.