Figure 1.

Locality map and relative generalized stratigraphy of the Doushantuo Fm. (A) Location of the Weng'an phosphorite deposits in Guizhou Province, China. Outcrops of the Doushantuo Fm are shown by the black areas. (B) Relative stratigraphy of the Terminal Proterozoic and Cambrian. The Doushantuo Fm is older than the late Neoproterozoic paleocommunity Zone III, which bears fossil evidence of cnidarian as well as bilaterian forms. Sponges are clearly present in Precambrian deposits (41, 42), including the Doushantuo (26). Beneath the Doushantuo Fm is a layer of tillite, deposited during the global glaciation, which is believed to have terminated about 590 Ma ago. On the left are interpolated absolute dates; the solid horizontal lines represent divisions dated by U-Pb geochronology. Also indicated are representative Cambrian lagerstätten. The dates shown for the Cambrian are from Landing et al. (43, 44) and Davidek et al. (45); the Precambrian/Cambrian boundary date is from Bowring et al. (30) and Grotzinger et al. (5). See text for discussion and references. The fossils shown are, from top to bottom: Opabinia, a middle Cambrian Burgess Shale arthropod; a Lower Cambrian olenellid trilobite (left) and Haikouella lanceolata (46), an early Cambrian chordate (right); a small shelly fossil of the Lower Cambrian; Arkarua, a possible Precambrian echinoderm (left) and a sea pen, Charniodiscus, from the later Precambrian (right); a possible sponge embryo from the Precambrian Doushantuo Fm (left), and a fossil embryo resembling a deuterostome gastrula (right; for more details see Fig. 3A).