Reply to Comment by Liu and Liu on “40ar/39ar Dating of Ignimbrite from Inner Mongolia, Northeastern China, Indicates a Post‐middle Jurassic Age for the Overlying Daohugou Bed”

[1] Liu and Liu [2005] have questioned our conclusion of the post Middle Jurassic age for the Daohugou bed [He et al., 2004], and instead suggested that the same deposit is equivalent to the Tiaojishan Formation of the late Middle Jurassic. Their arguments were mainly based on their own understanding of the Daohugou Biota-bearing sequences and a series of SHRIMP U-Pb ages of the zircon from the igneous rocks in the Daohugou area. Unfortunately, their comments have provided neither any new direct evidence from the field observation to falsify our sequence of the Daohugou Bed, nor any of the new dating which is in direct conflict with our dating results of the ignimbrites. [2] First, although there exists dispute over the interpretation of the Daohugou Biota-bearing sequence, there is little dispute over the Ar/Ar age of the ignimbrite in the Daohugou section by He et al. [2004]. Liu and Liu [2005] provided a series of SHRIMP U-Pb ages of the zircon ranging from 152–165Ma, which is, however, generally consistent with our dating result [Chen et al., 2004; He et al., 2004; Liu et al., 2004; Ren et al., 2002]. [3] Second, Liu and Liu [2005] referred one SHRIMP U-Pb zircon age (164–165Ma) of the tuff interbedded in the fossil-bearing shale [Yang and Li, 2004]. We had dated by ourselves the interbedded tuffs (arguably the same tuff as by Yang and Li) by Ar/Ar step-heating (Table 1 and Figure 1) and single crystal fusing by CO2 laser (Table 2 and Figure 2) on K-feldspars. Our dating results indicate that the tuffs were heavily contaminated by old crystals, thus explanation of the dating result should be made with caution. [4] Third, Liu and Liu [2005] also questioned our explanation of the sequence of the ignimbrite overlying the Daohugou deposits, and cited some references to argue that the deposits overlies the ignimbrites. Unfortunately, none of these authors has provided any evidence of direct contact between the ignimbrite and the Daohugou deposits in their papers [Liu et al., 2004], and neither have Liu and Liu done so in their comment. On the contrary, the weathered layer shown in our paper (the direct contact) between the ignimbrite and the fossil bearing shales [He et al., 2004] had, for the first time, provided convincing evidence to reveal the stratigraphic sequence in this region, which unambiguously indicated that the fossil bearing shales are younger than the dated ignimbrite as mentioned in our original paper [He et al., 2004]. [5] Fourth, our recent field investigation has clarified some observations while providing more evidence in support of our original opinion [Wang et al., 2005]. We have discovered a new locality (Jiangzhangzi, Wuhua, N 41 240 26.800; E 119 150 31.600) in Ningcheng, Inner Mongolia, where the fossil-bearing Daohugou bed deposits are found to be directly overlying the ignimbrites, indicates that the Daohugou bed is younger than the ignimbrite (Figure 3). The red or greenish shales and mudstone that were previously referred to the Tuchengzi Formation near the Daohugou village are now recognized as representing the lowermost deposits of the Daohugou bed (contrary to Liu and Liu’s [2005] suggestion of the upper or top part of the section), with a broad distribution than previously understood.