"16 And Pregnant" star Sean Garinger's official cause of death is blunt force injury to the head ... according to the M.E.'s office.
TMZ obtained the docs from the Raleigh, NC Medical Examiner's office, and the report on his February death says his skull was fractured in multiple places -- after his horrific freak accident involving an ATV in the driveway of his home.
As we previously reported ... Sean was driving his ATV when the ground gave way, flipping the off-road vehicle and pinning him underneath. The accident crushed his skull, tragically ending his life before help could arrive.
His family has since marked the accident site as hallowed ground -- and TMZ got the first look at the makeshift memorial with flowers and signs that read, "We Love You Squishy"—Sean's nickname.
Sean was on Season 6 of the show with his ex, Selena Gutierrez ... which chronicled their life after welcoming their 2 daughters, 3-year-old Dareli and 19-month-old Esmi.
Selena told TMZ their kids were too young to grasp what happened to their dad -- but she was grateful they got to spend time with him just a few weeks before he passed.