eustasy
A worldwide change in sea level, especially one caused by melting ice or tectonic activity.
The age of the dunal or other deposits, formed on it after the sea had begun to withdraw, in accordance with the theory of glacial eustasy, and which I have named Berardian, is, however, the crucial thing here.
Where it comes from
A back-formation from eustatic (borrowed from German eustatische (“eustatic”), from Ancient Greek εὖ (eû, “well, good”) + στάσις (stásis, “standing”)) + -y.
Adapted from the Wiktionary entry eustasy (CC BY-SA 4.0).