zompist bboard

The sporadic <au> for Modern English <a> before /n/ (straunge, Caunterbury), what did it indicate? Was there a diphthong in those words or maybe a back rounded vowel? I've been toying with an alternative orthography dating back to that period and I'm not sure how to transcribe the mentioned words.

Good question. Could it be nasalization? Or the rendering of a nasalized borrowing? [apparently straunge comes from Anglo-Norman estraunge, but idk what that means]