https://en.wikipedia.org/wiki/Eocene
The world map was broadly similar to todays back in early Eocene times (55 Ma) where the sediments in the referenced article are dated to. You have to go back a further ~200 million years before parts of Canada were physically in the tropics.
It is thought there was a big release of methane from seabed methane clathrates that put the globe into a strong greenhouse situation. Global temperatures were cooler before that event and cool again by the late Eocene.