TAPHONOMY OF THE ENIGMATIC EDIACARAN FOSSIL SHAANXILITHES: NEW EVIDENCE FOR A BODY FOSSIL AFFINITY

Shaanxilithes is an enigmatic ribbon-shaped fossil commonly found in great numbers in Ediacaran silty and calcareous shales in South China. Originally discovered near the town of Kuanchuanpu in Shaanxi Province, Shaanxilithes has been found at numerous sites in South China, North China, Chaidam, and southern Siberia, and is a potential index fossil for inter-regional biostratigraphic correlation of upper Ediacaran successions. This potential has been masked by divided affinities of Shaanxilithes, having been variously interpreted as a trace or a body fossil. Shaanxilithes is often preserved as a thin film along the bedding plane with no evidence of vertical intrusion into other bedding planes and containing little to no carbonaceous material. Through detailed microstructural and microchemical investigation using light microscopy, thin section petrography, environmental scanning electron microscopy, and energy dispersive X-ray spectroscopy, new details of the mechanisms of Shaanxilithes preservation are revealed. The new data show that Shaanxilithes is preserved as a clay mold in a phosphate-rich silty and calcareous matrix; this style of preservation shares some similarities with Ediacara-type and Burgess Shale-type preservation. Together with other taphonomic features, such as folded ribbons, overlapping but not cross-cutting ribbons, and possibly disarticulated ribbon sections, these microstructural and microchemical data suggest that Shaanxilithes is likely a body fossil rather than a trace fossil.