Name: Doushantuo Formation Location: South China Age: 550-590 million years old (latest Precambrian)

2. Geological Setting and Age

The Doushantuo Formation is Sinian in age (part of the Neoproterozoic, in the Precambrian Period) (Xiao et al., 1998a). The Sinian is made up, from the base, of: the Liantuo Formation (sandstone and conglomerate), the Nantuo Formation (mainly tillites - glacial debris that has been cemented into rock), the Doushantuo Formation (including limestones, phosphate rocks and shales), and the Dengying Formation (Yuan and Hoffmann, 1988).

The Doushantuo Formation is 250m thick in its type area (Zhang and Yuan, 1992), and it can be divided into two fossiliferous sequences. The lower Doushantuo sequence has been interpreted as a shallowing-upward sequence (Shen et al., 2000), as has the upper Doushantuo sequence (Xiao et al., 1998a). According to (Shen et al., 2000), the Doushantuo phosphorites were deposited in "relatively shallow environments along a Neoproterozoic, east-facing passive margin." (Shen et al., 2000, p. 771).

The Doushantuo Formation has been dated using its surrounding formations. Tuffs from the underlying formation have been dated at 736-760 million years old; and the ash beds in the overlying formation have been dated at 505-573 million years old (Shen et al., 2000). However, Qian, Chen and Chen (1979) found that acritarchs (spherical organic-walled microfossils) in the Doushantuo Formation could be correlated with other, better-dated successions. These successions indicate a date for the Doushantuo Formation accumulations, of 550-590 million years ago (Qian, Chen and Chen (1979).

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