According to the Amtrak tracker, there are currently two Amtrak trains in Michigan. One going westbound from Detroit towards Battle Creek is traveling at 63 MPH, and one Eastbound from Battle Creek towards Jackson traveling at 57 MPH.
Looking at the history of both trains, they are both about an hour and a half late, but both were essentially on time until about 11:30 AM.
So whatever caused the hour-and-a-half stoppage appears to have been cleared up.