ESPN's Adam Schefter first reported the news.
When asked whether he tried to get Turner to remain with the team, head coach Mike Zimmer said the two had a long talk but Turner was set in his decision, per Rand Ball of the Star Tribune.
"He's been my right-hand man," Zimmer said, per Albert Breer of The MMQB. "I was very, very surprised."
On Sunday, CBSSports.com's Jason La Canfora provided insight into Turner's departure:
Differing philosophies over how to direct the Vikings offense out of a recent funk led to [Turner's] surprising decision to resign from [Zimmer's staff], league sources said. The decision caught virtually the entire organization off-guard. Turner was not pushed to leave midway through his third season with the Vikings (5-2), contrary to some reports, but expressed a belief it may be best for all parties if Minnesota moved on without him given differences over the team's scheme and how to rebound after consecutive lopsided defeats.
Turner actually had a strong working relationship with [Shurmur], the tight ends coach before Turner's departure, according to multiple team sources.
Quarterback Sam Bradford said he found out from his wife, who received an alert on her phone, per Pro Football Talk.
"I feel bad for Norv," an unnamed Vikings player said following the announcement, per Ed Werder of ESPN. "Wish I could have done more to help this offense so we wouldn't be in this situation."
Minnesota is 5-2, but since starting the season 5-0, it has averaged 10 points per game in losses to the Eagles and Bears.
The Vikings are tied for 23rd in the NFL with 19.9 points per game and are 31st with 293.3 yards per contest.
With superstar running back Adrian Peterson on the shelf with a knee injury, the ground game has suffered significantly, as Minnesota ranks 31st with 71.9 rushing yards per game.
In addition, offensive tackles Matt Kalil and Andre Smith were placed on injured reserve, while quarterback Teddy Bridgewater was lost for all of 2016 just prior to the start of the regular season.
The 64-year-old Turner has been the offensive coordinator since 2014, and running the football was the team's specialty for much of his tenure.
Minnesota was fourth in rushing last season with Peterson at the helm, but the combination of Matt Asiata and Jerick McKinnon has struggled in his absence.
Bradford has eight touchdown passes and just one interception, but his efficiency has dropped over the past two games. He posted a QBR of 7.6 against the Eagles and 20.9 against the Bears, per ESPN.com.
Minnesota remains in first place in the NFC North thanks to an elite defense that ranks first in points allowed per game (14.9) and second in yards allowed per game (297.1).
The Vikings are threats to make a deep run in the playoffs if the offense can become more efficient, and moving on from Turner is a potential quick fix that could provide a boost.
He figures to land a job elsewhere in the near future if he so chooses, especially since Peterson's injury affected what he was able to do in Minnesota.
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