According to the death certificate released by the Los Angeles County Department of Public Health, obtained by TMZ ... the official cause of death is pancreatic cancer -- which happens to be the 4th leading cause of cancer deaths in the country.

According to the doc, there were no other contributing factors to his death.

This update comes more than a week after the music titan, who worked with everyone from Michael Jackson to Frank Sinatra, died at his home in Bel-Air, in Los Angeles, California at the age of 91.

Quincy's publicist, Arnold Robinson, confirmed the sad news to TMZ at the time ... sharing QJ was surrounded by his family when he died.

The family issued a joint statement following Quincy's passing, revealing his death was "an incredible loss" for them all.

They added ... "We celebrate the great life that he lived and know there will never be another like him."

Quincy's daughter, "Parks and Recreation" star Rashida Jones, penned her own tribute to the music legend on Instagram ... remembering him as an "icon," "culture shifter," and a "genius."

Quincy was laid to rest in Los Angeles in a private ceremony attended by his 7 children, his brother, 2 sisters, and other family members. The family confirmed a public celebration of life would also be held ... but no date has been announced.

They previously requested that, in lieu of flowers, donations be made in Quincy's name to the Jazz Foundation of America.