This is the score in question:
And this is my attempt to translate it to clefs I'm familiar with:
It should be noted that the whole structure is kind of harmonic ornamentation of the C chord (which precedes this section). Assigning a chord symbol to every vertical structure might be a bit of an overkill. But let's try anyway.
For a chord containing strictly the notes G-D-F-A there are in general three possibilities:
- Dm/G (read: D-minor chord with G in bass)
- G7sus2 (read: G7 chord: G-B-D-F with third, B, replaced by second A)
- Dmadd11 (D-minor with added G)
The fourth possibility is suggested by Tim: Dm11. It means a D-minor chord with added 11 (F), which also may contain flat 7 (C). And guess what, horns are holding that C! so it's not bad choice either
My choice would be Dm/G or Dm7/G (thus including C), because it's the most compact symbol, and indicates the bass note.