Root, who finished the day on 111 not out, refused to divulge what Gabriel said when asked about the incident at the end of day's play, saying it should stay on the field.
'It's Test cricket. He's an emotional guy trying to do everything he can to win a Test match. "Sometimes people say things on the field that they might regret", the report quoted Root as telling reporters. "I don't want anything said in the middle to ruin what's been a good Test series for him and his team", Root added. "The battle was a good contest".
"Gabriel already had five demerit points against his name for two earlier incidents - three demerit points during the Jamaica test against Pakistan in April 2017 and two demerit points in the Chittagong test against Bangladesh last November", the ICC said in a statement.
It takes Gabriel's total demerit points to eight in a two-year period, resulting in a four-match ODI ban.
Injuries to key players meant he may well have been recalled before the punishment was handed down.
Gabriel reportedly called Root a "b**** boy" in a confrontation with the England captain when he was batting on Monday, although a West Indies source told Sportsmail that he said "little boy". "What [prayer] have you got her to say for you today?"
Meanwhile, fellow MP Johnny Mercer hailed Root's "moral courage" in a tweet, while Nigel Owens, who came out as gay in 2007 and refereed rugby union's World Cup final in 2015, said Root's response was "wonderful and hugely important".
Gabriel was not included in the initial squad for the five ODIs against England but the Windies had made it clear he would be added after a brief rest period and meant to call up the 30-year-old as injury cover for Keemo Paul and Rovman Powell.
West Indies head coach Richard Pybus, speaking at close of play, told BBC Radio's Test Match Special: "Nothing has been reported to me but if a comment was made we'll review it and if it was untoward we'll be addressing it".
"It's always a proper tussle out there".
"I just did what I thought was right".
"Shannon is a proper old-school fast bowler, I think we need to find out if there is anything behind the rumours and then we'll address it".