Tian Gan, Guanghong Zhou, Taiyi Luo, Ke Pang, Mingzhong Zhou, Weijun Luo, Shijie Wang, Shuhai Xiao

Speleothems can offer insights into terrestrial life because their formation is critically dependent on soil-microbial ecosystems. Here we report the wide distribution of miniature paleo-speleothems from the ~635 Ma Doushantuo cap dolostone in South China in order to understand the recovery of terrestrial life after the terminal Cryogenian Marinoan snowball Earth glaciation. The cap dolostone was deposited during the initial transgression following deglaciation, but subsequently developed extensive karstic cavities or sheet-cracks when the cap dolostone was brought to the phreatic zone during post-glacial rebound. The sheet-cracks were filled with multiple generations of cements, including isopachous dolomite formed in the phreatic zone and speleothems formed in the vadose zone. The paleo-speleothems are millimeters-centimeters in size and include stalactites, stalagmites, helictites, moonmilk, flat crusts, and botryoids. The speleothems were silicified by subsequent hydrothermal processes, which also precipitated the chalcedony and quartz in the sheet-cracks and occurred before a renewed transgression in which ~632 Ma shales overlying the cap dolostone were deposited. The wide distribution of paleo-speleothems indicates the presence of an active soil-microbial ecosystem in the earliest Ediacaran Period and in the aftermath of the Marinoan snowball Earth.