primeval chaos
沌 centers on a state of undifferentiated, formless confusion: the primeval chaos before order emerged.
沌 combines the water radical 氵 with 屯, which likely contributes the sound. The compound suggests a watery, murky state of confusion, fitting the idea of primeval chaos.
Water 氵 mixed with the tangled shape 屯 creates a murky, swirling mess: primeval chaos before things settled into order.
For トン, imagine a ton of chaotic water swirling together: ton -> トン, and the heavy mass is formless confusion.