9:15 AM - 9:30 AM
[BPT27-02] When did the "Cambrian agronomic revolution" start?
Keywords:Ediacaran, Cambrian, ichnofossil, Cambrian explosion, Cambrian agronomic revolution
Upper Proterozoic to Cambrian deposits are widely distributed in the Govi Altay area in western Mongolia. In the Bayan Gol valley, we found large-sized Arenicolites isp. with vertical burrows from as many as 11 horizons in the Ediacaran bedded limestones. These burrows reaches 4 cm in maximum in vertical orientation. We collected rock samples in 2 m interval, for the carbon isotope stratigraphy.
The horizons with Arenicolites isp. are in the bedded limestone of the upper Tsagaan Oloom Formation. They are located at 190-140 m lower than the base of the Cambrian determined by the first occurrence of the ichnofossil Treptichnus pedum in this section, and at 120-70 m lower than the horizon of the "BACE event", which is characterized by a clear negative excursion and is correlated approximately to the horizon of the Pc/C boundary. It is clarified that the ichnofossil Arenicolites isp. with vertical structure certainly occurs from the Ediacaran as opposed to the previous interpretation. This shows that "The Cambrian agronomic revolution" had already begun in Ediacaran in western Mongolia. This early start of this revolution can be attributed to the geographic position of Mongolia in late Ediacaran-early Cambrian, because Mongolia was located near the equator under warm environment during this interval.