That would be Bronze Age actually. Modern fans have a tenancy to act as though everything was the Silver Age until 1986 when Miller and Moore dropped out of the sky and made rated R superhero comics.
I am aware of the Silver/Bronze/Golden/Modern ages of comics. Claiming I am a modern fan is only true in the instance that I was not born in 1933.
I am aware that the first Superman film was made in 1978, late in the bronze age.
But the ideas in that movie were more based on the ideas of the Silver Age than the Bronze Age.
Bronze Age Superman couldn't move the moon in Superman 4 with that much ease.

He was vastly weakened from Silver Age.
Silver Age Superman once said after a vacation turned into a lot of danger, "Next time I want a vacation, I'll pick a safer place, like an exploding sun!"
Bronze Age Superman was knocked out by a Supernova. Silver Age Superman would laugh in the face of the Big Bang.
And since Superman Returns borrows from the first two movies, and the first movie had insane exaggerations of Superman's powers, from stopping the Earthquake by lifting up the continental plate,

something Bronze Age could do, but he wouldn't do it without complaining a bit.
Also, he spun the Earth backwards on it's own axis. This is a massive exaggeration of his Silver Age Superman power to turn back time like it was nothing.
Bronze Age Superman could have never pulled that off. Only Silver Age could have an exaggerated ability to change the Earth's rotation, create a temporal rift, and reverse time like that.
I know Bronze Age was awesome powerful, but Silver Age Superman could beat up the Anti-Monitor.
Also, Superman Returns also had Clark lift up the massive continent of rock and Kryptonite, and hurl it into space.
Only Silver Age Superman's ability to use his powers if he really concentrated on them under the influence of Kryptonite would allow him to do that.
First introduction of Metallo, in 1959 proves my point.
Superman was exposed to a Kryptonite rod, and to counteract it, he had to use his heat vision on it until it melted. Six hours later.

He recovered somewhat fast.
Bronze Age would have collapsed, just like Modern Age Superman from being too close to Kryptonite.
And only Silver Age Superman could perform the lifting of the continent up into the air. Especially with a piece of Kryptonite in his body.