Seismic is exactly the right word for it. From Joe Lauria at consortiumnews.com:
The Chinese-brokered diplomatic deal between Saudi Arabia and Iran not only opens the way for resolution of region-wide conflicts, but foils U.S. Mideast designs based on Saudi-Iranian enmity, writes Joe Lauria.

King Salman greets Chinese President Xi Jinping. (Chinese Foreign Ministry)
Ever since the 1979 Islamic Revolution that overthrew the U.S.-allied Shah of Iran, the rivalry between the two major Middle East powers — Iran and Saudi Arabia — has been at the heart of every conflict across the region.
The announcement on Friday that Iran and Saudi Arabia have normalized relations could have a seismic effect on all these conflicts and leave the U.S. on the outside looking in.
In Lebanon, Iranian-backed Hezbollah and Saudi-backed parties might begin to resolve their differences, a unity that would worry Israel and lessen U.S. influence in the country.
In Syria, Hezbollah and Iranian militias have been battling Saudi-backed jihadists for more than a decade. The Syrian war could now come to an end.
In Yemen, U.S.-backed Saudis have been fighting the Houthi, who have been driven into a closer alliance with Iran. Obstacles to a peace deal could now have been removed.
In Iraq, reconciliation between Sunni and Shia could make the U.S. presence and influence irrelevant and unwelcomed by all sides.
In Bahrain, Iranian-backed Shi’ites no longer in conflict with the Saudi-aligned monarchy could sideline the presence of the U.S. Fifth Fleet in a region on the mend.
And in Saudi Arabia itself, the state’s tensions with Shi’tes in the eastern oil regions should lessen.