Friday, October 23, 2015

Ediacaran Oceanic Oxygenation may be Older Than Previously Thought

Stratigraphic position of the Ediacaran Miaohe biota and its constrains on the age of the upper Doushantuo δ13C anomaly in the Yangtze Gorges area, South China


An et al


The siliceous shale unit that hosts the Ediacaran Miaohe biota in the Yangtze Gorges area, commonly referred to as the Miaohe Member, has an age of 551 ± 0.7 Ma. This unit is thought to be time-equivalent with the Doushantuo Member IV, which marks the top of the upper Doushantuo negative δ13C excursion. New bio-, sequence- and chemostratigraphic studies presented here demonstrate that the Miaohe Member is significantly younger than the Doushantuo Member IV, most likely time-equivalent with the lower Shibantan Member of the Dengying Formation. The new findings indicate that the top of the Doushantuo Formation, i.e., the top of the upper Doushantuo/Shuram δ13C excursion, should be much older than 551 Ma (likely ≥ 560 Ma). The ocean oxygenation event documented from the Doushantuo Member IV black shales should also be older than 560 Ma and predate the Miaohe biota for more than 10 Ma.

No comments: