Via the turtle, Thomas Westerhold et al. "An astronomically dated record of Earth’s climate and its predictability over the last 66 million years" doi 10.1126/science.aba6853.
They're looking at plankton-shell formations, "benthic foraminifera". They hold records of carbon and oxygen isotopes. Such work been done before but - they say - it was only good from 34 mya to now. This one spans back to the latest Cretaceous and, yes, they do see Chicxulub 66 mya in there. But it's nowhere near as drastic as the Palaeocene / Eocene hot spike 56 mya, interestingly. h/t Ineffable Island.
Palaeocene was a "warmhouse" 5 C higher than now; followed, after the spike, by the 56-47 kya "hothouse" aka Climate Optimum. Then within this same Eocene, Warmhouse II - 47-34 mya. Oligocene-Miocene is marked "Coolhouse" until 3.3 mya when we enter the Icehouse but, as noted, we already knew that.
The Miocene hosts the middle-Miocene transition at 13.9 mya. That's West Antarctica, attracting ice so raising that half this planet's albedo. The counterpodal Arctic has no landmass on this scale (Baffin? Greenland? ...Svalbard -?) so the northern hemisphere is marked by instability.
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