The phrase "a calamitous turn" is correct and usable in written English.
It can be used to describe a situation that has taken a disastrous or unfortunate change.
Example: "The project was going well until it took a calamitous turn, leading to significant setbacks."
Alternatives: "a disastrous turn" or "a tragic turn".
Such an outcome here would signal a calamitous turn away from democracy for Ukraine, she said, but added that, "I am ready for anything".
Once a bright 17-year-old bound for M.I.T., she had taken a calamitous turn while drinking and driving, a detour that sent her to prison.
The God's Army's fortunes took a calamitous turn after it became enmeshed with an even more fringe group that led attacks on Myanmar's embassy in Thailand in 1999 and a Thai hospital in 2000.
The battle to reverse the calamitous turn that the American diet has taken is long and uphill.
This being the Balearic Islands, and they being English and full of booze and drugs things take several utterly calamitous turns.
The Houston Texans have turned a calamitous season into one streaking toward a potential playoff berth.
That pause isn't unusual: Frank is a thoughtful talker, carefully considering every answer, the sort of calm presence that could easily turn around a calamitous run when others might have panicked.
In a calamitous shift of emphasis, Ritchie turns Kuryakin into a semi-psychotic.
The timing of Margaret Hodge and Ann Coffey's motion of no confidence was too rash, and triggered a calamitous leadership challenge which has turned out to be a self-inflicted wound.
But a rocky June turned into a calamitous July, and by the end of the month, Sowood was on the brink of collapse.
He and his partners, dealing with the wreckage of a calamitous September collapse for the Red Sox, must hope buying Liverpool does not turn out to be a curveball.
