This ornamentation 1st appeared on 2pc. plates 1830. It’s oak leaf and acorn background was part of a common 1840-1850 stock pattern. This was the latest style of plate displaying the Army’s button motif on the breast shield of the Eagle. The eagle on this buckle is facing the olive branch.
“American Military Belt Plates, 1st and 2nd Ed.”, by O’Donnell & Campbell, Pg. 205, plate 309.