NEW MULTICELLULAR ALGAL FOSSILS AND ACRITARCHS IN DOUSHANTUO CHERT NODULES (NEOPROTEROZOIC; YANGTZE GORGES, SOUTH CHINA)

Abstract

The late Neoproterozoic Doushantuo Formation in South China contains several exceptionally preserved biotas in its cherts, phosphorites, and black shales (Xiao et al., 1998b, 2002; Zhang et al., 1998). The three taphonomic windows—silicification, phosphatization, and carbonaceous compression—responsible for most of the preservation of nonbiomineralizing organisms in geologic history are all open in the Doushantuo Formation. In combination, these three taphonomic windows have the potential to give us a clearer and more complete picture of late Neoproterozoic biodiversity. Comparison across the three also allows us to evaluate possible taphonomic biases and paleoecological heterogeneity. To accomplish these, however, a more thorough paleontological investigation of each taphonomic facies is necessary. Monographic studies on Doushantuo shales, cherts, and phosphorites (Steiner, 1994; Zhang et al., 1998; Xiao et al., 2002) demonstrate that macroscopic (millimeter to decimeter) fossils are typically preserved as carbonaceous compressions, while microscopic (micrometer to submillimeter) fossils are preserved as permineralized (silicified and phosphatized) forms. Published reports also indicate that, although both the silicification and phosphatization windows preserve microscopic organisms, taxonomic compositions of the silicified and phosphatized biotas appear significantly different. Doushantuo phosphorites contain a plethora of multicellular eukaryotes (algae and animals), a moderate diversity of acritarchs, and relatively few cyanobacteria filaments. In contrast, coccoidal and filamentous cyanobacteria and acritarchs are abundant and diverse in Doushantuo cherts; multicellular eukaryotes are comparatively rare in Doushantuo cherts (Table 1). View this table: Table 1 —List of prokaryotes, acritarchs, multicellular algae, and animal fossils from upper Doushantuo chert nodules in the Yangtze Gorges area and upper Doushantuo phosphorites at Weng’an and elsewhere in South China (updated from Zhang et al., 1998). Synonyms are not listed Since the monographic study of permineralized microfossils in Doushantuo cherts and phosphorites (Zhang et al., 1998), several reports of new microfossils and new localities have appeared in the literature …