A sudden surge in the concentration of carbon dioxide in the air and the ocean 56 million years ago may have triggered the Paleocene-Eocene thermal maximum (PETM), a period of rapid and dramatic warming. In conjunction with the rising atmospheric temperature, ocean acidification significantly increased the dissolution, or “burndown,” of carbonate sediments on the seafloor, destroying the preservation quality of seafloor foraminifera shells.
Schultz C., 2013. A selective approach to draw data from altered foraminifera shells.Eos, Transactions American Geophysical Union 94(45):420. Article (subscription required).