MERCURY ANOMALOUS EVIDENCE FOR STRONG VOLCANISM IN LATE-NEOPROTEROZOIC BEFORE THE RISE OF ANIMAL LIFE

Following earth’s most severe glaciations, the Ediacaran period (635 to 542 Ma ago) witnessed a time of fundamental environmental and evolutionary change. Before the Ediacara biota developed at ~580Ma, the environment may be still hostile and nonpermissive for animal evolution. Here we selected two sections which developed well Nantuo to Doushantuo Formation successions, namely Zhangshuping and Siduping sections in South China, and systematically established mercury chemostratigraphy. Results show that Mercury (Hg)/total organic carbon(TOC) present rather high values, up to a maximum of 5.0 (ppm/wt%) in Nantuo formation of glaciation. The relatively high values, go through the upper capdolomite and continue to the Doushantuo formation Ⅱ member. In ascending order, Hg/TOC generally keep relative lower values less than 0.4 with slight fluctuation through two sections. The High Hg/TOC values was interpreted to be related with strong volcanism in that period, maybe because of earth's crust active movement. This may be the first time that evidence has been produced that volcanism may be related to the Nantuo formation of glaciation. The early Ediacaran ocean with high Hg levels is logically toxic and not avail to the animal evolution. Ediacara biota could well develop after the earth entered into a status with less volcanism and permissive environment for animal evolution. This research result may imply the causal relationship between crustal evolution and coeval environment, climate and animal evolution.