in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
Astronomical Calibrated Time Intervals for the Non-marine
Badaowan Formation, Lower Jurassic in Haojiagou of Ürümqi City,
Western China
22
Jingeng Sha 1
, Daoyi Xu 2
, Xiaogang Yao 1
, Yanhong Pan 1
, Yaqiong Wang 1
,
Xiaolin Zhang 1
, Bo Peng 1
1. LPS, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
(E-mail: jgsha@nigpas.ac.cn)
2. Institute of Geology, China Earthquake Administration, Beijing 100029, China (E-mail: xdy505@tom.com)
The thick coal-bearing sediments of Badaowan
Formation (BF) accumulated at Haojiagou (about 50
km southwest of Ürümqi City), Northern Xinjiang, are
very well exposed and structurally only slightly de-
formed. It is near 800 m thick, conformably resting on
the Haojiagou Formation (Late Triassic) and dis-
conformably underlying the Sangonghe Formation
(Early Jurassic) (Zhang, et al., 2003; Lu and Deng,
2005; Huang, 2006; Sha, et al., 2010).
Lithologically the BF at Haojiagou section can be
subdivided, from bottom to top, into three members,
Lower Member (LM), Middle Member (MM) and
Upper Member (UM). The LM and UM of BF are
predominantly fluvial sediments, and the MM of BF is
characterized by lacustrine deposits. On the basis of
palynology, the Triassic−Jurassic boundary has been
located between underlying Haojiagou Formation (HF)
and BF (Lu and Deng, 2005; Sha, et al., 2010).
Table 1 Comparison of calculated dominant periods of LM of BF and upper part of HF to the related astronomical periods
Astron. Period/ kyr
Dominant period
Thickness/m Time/ kyr
Deviation/ kyr
978(Ec 7) 81.9 973 5
405(Ec 1)
131(Ec 5)
34.1 ( 405 )
124(Ec 3)
99(Ec 4)
10.2 121.1 2.9
95(Ec 2)
46.3(Ob 3)
36.5(Ob 1)
35.4(Ob 2)
8.03
3.94
3.03
95.4
46.8
36.0
-0.4
-0.5
0.5
26.6(Ob 4)
22.1(Pr 2)
21.0(Pr 1)
17.9(Pr 3)
15.7(Pr 4)
2.09
1.83
1.72
1.42
24.8
21.7
20.4
16.9
1.8
0.4
0.6
1.0
Note: Ec-Eccentricity; Ob-Obliquity; Pr-Precession. The number followed after alphabet (1, 2, 3, ...7) indicates that the
contribution of defined cycle in the spectrum decreases from larger to smaller.
The BF demonstrates a series of regular sedi-
mentary cycles, which has been attributed to orbital
climatic (Milankovitch) cycles. In this study, a cyclo-
stratigraphic investigation, using lithologic variations
in the Lower Jurassic terrestrial deposits of the BF and
also upper part of HF based on the field investigations,
spectral analysis and digital filter results, was employed
to: (1) test for regular cycles; (2) establish an astro-
nomically calibrated time intervals for Badaowan
Formation; (3) independently determine microrhythmic
(cyclic) comparison between LM of non-marine BF and
marine Blue Lias deposits in south England.
As the period of 405 kyr (405EC) is the most
stable of the orbital cycles over geological time (Olsen
et al., 1996), and it is characterized by largest amplitude
in the eccentricity, Laskar (2004) suggested it may be
used for the calibration of the Mesozoic time scale.
An average duration of BF is 6.07 Myr, and the
duration of LM of BF is 3.03 Myr, which is very
consistent with the current estimation of the duration of
the Hettangian Stage (3.10±0.8 Myr).
There are 65 obliquity cycles which have been
recognized from the LM of BF, and the obliquity cycles
are also remarkable in LM of BF. Such obliquity cycles
could be cyclically compared to the 65-67 micro-
rhythms within three ammonite zones in Hettangian