solarpunk memes

Probably not. It's likely carbon that is pretty much completely oxidized since OP said it was captured as a byproduct of industrial activity (after all, why would you sequester carbon that still had useful energy?) If you store fully oxidized carbon underground for millions of years, it will still be fully oxidized when it's dug up because that carbon's most stable state (especially in an oxygen-rich environment like Earth). The only reason fossil fuels exist is because the carbon was sequestered in a mostly reduced (aka energy-rich aka unstable) state, so you get a mess of goopy hydrocarbons after millions of years. If you try the same thing with CO~2~, you just get limestone.