Reloaded using autosave but forgot to make a proper savegame, so the autosaves before turn 72 was lost. Continued playing for a couple of turns, until the game froze at the start of turn 102. Loaded the latest autosave, and saved it properly. But I wasn't able to reproduce the crash despite trying a couple of times.
The log only mentions warnings regarding combat and barbarian units, like Peltasts. I thought it might have to do with the fact that the Global Era changes to Classical at the start of turn 102, but the log doesn't mention anything as far as I can tell.
From now on, I'm going to enable all debug logging in GCO_ModUtils, in case I get a crash.