Based on this article it would seem that the transition from a unified people into two groups, Ashkenazim and Sephardim, began in the 9th century and proceeded over time. I would like to know if there is any demarcation as to when these groups were formally viewed as separate, so for example Rabbinic bans enacted by one group would not apply to the other. By way of analogy there are individuals who are seen as the last of a certain era (Tanaaim, Geonim, Rishonim etc.) these people can be viewed as demarcating between one epoch and another even though there was a transition which may have taken years. Does such a thing exist in terms of the split between Ashkenaz and Sephard?