UPDATE: Bungie has posted a notice about Marty O'Donnell's departure, saying the following:
For more than a decade, Marty O“Donnell filled our worlds with unforgettable sounds and soundtracks, and left an indelible mark on our fans. Today, as friends, we say goodbye. We know that wherever his journey takes him, he will always have a bright and hopeful future.
We wish him luck in all his future endeavors.
Marty O'Donnell has long been the man behind Bungie's legendary soundtracks for the Halo games and Destiny, but it seems that that has all come to an end now. The celebrated composer tweeted tonight that Bungie's board of directors had terminated him without cause.
The motive behind O'Donnell's termination is unclear at the moment, and Bungie has yet to make a comment on these developments but we'll keep you updated as more information comes in.
Image Source: Giant Bomb