in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
Toward the Stratigraphic Correlation and Reconstruction of
Atmospheric pCO2 in Terms of Stable Carbon Isotope in the
Terrestrial Jurassic Carbonates, China
H. Hirano 1* , G. Li 2 , T. Sakai 3 , T. Kozai 4 , H. Ishiguro 5
1. Waseda University Tokyo, Japan (E-mail: hhirano@waseda.jp)
2. Nanjing Institute of Geology and Palaeontology, CAS, Nanjing, China
3. Kyushu University, Fukuoka, Japan
4. Naruto University of Education, Naruto, Japan
5. Waseda University, Tokyo, Japan
We have been studying the non-marine middle and
late Mesozoic in China from the bio-, stable carbon
isotope-, and sequence stratigraphic points of view. In
2009, we collected samples from the lower to upper
Jurassic in and around Heibei, Chongqing, Sichuan
Provinces for the international correlation by using the
fluctuation curve of the stable carbon isotope as well as
for the reconstruction of atmospheric pCO2 by cal-
careous concretions in paleosols.
The non-marine lower Jurassic Ziliujing, Middle
Jurassic Xintiangou, Lower Shaximao, and upper
Jurassic Upper Shanximao Formations (Liet al., 1997)
distributed in the studying area. This age correlation is
based on dinosaurs (ditto). For the stable carbon isotope
stratigraphy, we collected samples from the Daanzhai
Member of the Ziliujing Formation. The member is
lacustrine beds composed of quarts grains with car-
bonate matrix.
We have tried high resolution correlation by using
stable carbon isotope curves for the non-marine lower
Cretaceous which is correlated with the Jehol Group in
Heilongjiang, Jilin, Liaoning, and Hebei Provinces.
We obtained δ 13 C from the terrestrial organic matter in
visual kerogen contained in mud stones of those beds.
This method is based on the successful results which we
conducted for the marine Cretaceous Yezo Group
distributed in Hokkaido, Japan.
Ninety-nine percent of visual kerogen is composed
of terrestrial organic matter in the marine Cretaceous
Yezo Group (e.g. Uramoto et al., 2007, 2009). There-
fore, it is not always difficult to obtain the d13C of
terrestrial organic matter in the Group for the
stratigraphic correlation. However, in the non-marine
lower Cretaceous of northern China often the ratio of
terrestrial organic matter is low and there is much
amount of algae (e.g. the Jiufotang Formation, δ 13 C
values range from -29 per mil to -23 per mil; in some
levels the amorphous organic matter occupies 98% of
TOC).Algae show different δ 13 C values from terre-
strial organic matter. Therefore, it is often impossible
to make stratigraphic correlation by using the stable
carbon isotope fluctuation. It is necessary to develop
the method to remove algae from the visual kerogen by
using specific gravity separation, which we are trying.
Additionally, the lower Cretaceous which is famous by
well preserved fossils like feathered dinosaurs contains
too much amount of tuff and the total organic carbon
contents are relatively smaller amount. It is also
difficult to obtain δ 13 C from such beds.
It is desirable to make cross checks for the
obtained correlation by stable carbon isotope from
various aspects. In the case of the Yezo Group,
ammonoids, inoceramid bivalves, planktic foraminifers,
radiolarians, sporopollen, dinoflagellates and radio-
metric method were used for the cross checks and the
validity was confirmed (e.g. Uramoto et al., 2007,
2009).In the case of the Chinese non-marine beds, the
validity of the obtained excursion curve of stable
carbon isotope would be checked by some marine
organisms which are sometimes found in the marine
invasions.
The analytical results of the terrestrial lower
Jurassic Daanzhai Member (carbonate matrix) do not
show the negative spike of the early Toarcian anoxic
event (Jenkyns, 1988) which continued for 500,000
years. The analytical values are different from the
expected values. We are now considering it.
We also began to reconstruct the atmospheric
pCO2 of Jurassic and Cretaceous by using calcareous
concretions obtained from the paleosols. For Jurassic,
we have studied the pCO2 by samples from the above
mentioned Jurassic in and around Beibei district. The
analytical results are fairly concordant from various
data obtained in the world. At present, we are
analyzing concretions and calculating the raw data.
We would like to show you the results at the time of the
symposium.
Key words: Stable carbon isotope stratigraphy;
International Correlation; Atmospheric pCO2; Ter-
restrial Jurassic
References:
Hesselbo S.P., Grocke D.R., Jenkyns H.C., et al.
Massive dissociation of gas hydrate during a
Jurassic oceanic anoxic event. Nature, 2000, 406:
392-395.
Jenkyns H.C. The early Toarcian (Jurassic) anoxic
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