Origin of K-bentonites in the Doushantuo cap dolostones from South China and its potential link with the sedimentary model of the Marinoan cap dolostones

•Source magma of K-bentonite in Doushantuo cap dolostone at Jiuqunao is rhyodacitic.•Source magma of K-bentonite in Doushantuo cap dolostone at Heyu is pantelleritic.•Two episode K-bentonites in Doushantuo cap dolostone have been identified.•K-bentonites have potential significance to the genesis of Marinoan cap dolostone.