Norv Turner Steps Down as Vikings OC

In what certainly is another shocking bit of news in the NFL, Vikings offensive coordinator Norv Turner is stepping down at the position and will be replaced by Pat Shurmur, who will carry an interm tag.
The #Vikings are announcing soon that OC Norv Turner is resigning, source said (as @AdamSchefter reported). No other changes.
— Ian Rapoport (@RapSheet) November 2, 2016
Pat Shurmur is the interim OC for the #Vikings, source said
— Ian Rapoport (@RapSheet) November 2, 2016
This comes as a surpriss, considering the Vikings offense has been effective enough to bring them to a 5-0 record, but two consecutive losses to the Philadelphia Eagles and Chicago Bears, combined with the fact that their offense is the 4th-least efficient offense in the league (per NFL FPI), lead to this.
Turner is a former head coach with the San Diego Chargers, Washington Redskins, and Oakland Raiders, and joined the Vikings in 2014. Norv has been coaching since 1975 when he took a job at Oregon.
Pat Shurmur has some familiarity with QB Sam Bradford. He worked with him as OC of the then St. Louis Rams in 2009 and as OC/interim HC with the Eagles in 2015. He was the tight ends coach with the Vikings this year until his promotion. He has been coaching since 1990 when he held multiple positions with the Michigan State Spartans.
Turner released this statement regarding his resignation: