Two great sequestration periods occurred since the mid-Paleozoic and both appear to coincide with evolution of plants. The first woody plants and trees arose in the Middle Devonian and fueled the large coal swamps of the Carboniferous Period. Later explosion of the flowering plants (angiosperms) occurred in the Cretaceous. All the while additional C was being locked up in limestones. Also in high TOC (Total Organic Carbon) muds that were converted to the shale/mudrocks that we are now liberating with fracking.
Gregory R. Wrightstone