Cryptic terrestrial fungus-like fossils of the early Ediacaran Period.

The colonization of land by fungi had a significant impact on the terrestrial ecosystem and biogeochemical cycles on Earth surface systems. Although fungi may have diverged ~1500-900 million years ago (Ma) or even as early as 2400 Ma, it is uncertain when fungi first colonized the land. Here we report pyritized fungus-like microfossils preserved in the basal Ediacaran Doushantuo Formation (~635 Ma) in South China. These micro-organisms colonized and were preserved in cryptic karstic cavities formed via meteoric water dissolution related to deglacial isostatic rebound after the terminal Cryogenian snowball Earth event. They are interpreted as eukaryotes and probable fungi, thus providing direct fossil evidence for the colonization of land by fungi and offering a key constraint on fungal terrestrialization.

Timing the termination of the Doushantuo negative carbon isotope excursion: evidence from U-Pb ages from the Dengying and Liuchapo formations, South China.

The Doushantuo negative carbon isotope excursion (DOUNCE) is the largest known marine inorganic carbon isotope anomaly. The origin of this pronounced negative excursion is still an enigmatic issue that attracts geologists. Time constraints on the excursion are the critical information that would provide insight into its genesis. In previous decades, the timing of its termination has been constrained by the widely cited zircon U-Pb age of 550.5 ±â€¯0.8 Ma for the tuff at the top of the Miaohe Member at the Jiuqunao section in the Yangtze Gorges area, South China. However, results of recent studies indicate that the reliability of this time constraint needs to be re-evaluated. Here, a geochronological study was carried out using two K-bentonites from Fanglong in South China. A K-bentonite in the lower Dengying Formation yielded a U-Pb age of 557 ±â€¯3 Ma, while a K-bentonite in the basal Liuchapo Formation yielded an age of 550 ±â€¯3 Ma. Based on regional correlations between the Ediacaran successions in South China, the age (557 ±â€¯3 Ma) for the K-bentonite in the lower Dengying Formation may serve as a second critical timing constraint for the ending of the DOUNCE. Combined with available estimates of the DOUNCE duration, our new data indicate that the DOUNCE has a maximum onset age ∼570 Ma.