[geordief (OP)]

Can we call spacetime a field or is it just a coordinate  system?

Do  all the local curvatures  of spacetime  constitute  a field?

If so ,is it possible to apply the description"an excitation  of the field" to this gravity/spacetime curvature  field and ,if so what would we be talking about?

[evan_au]

"an excitation  of the field" to this gravity/spacetime curvature  field

Excitations of gravity (and gravitational time dilation) can travel through spacetime.
- This is the hypothetical graviton
- With our current technology, we have no way of detecting individual gravitons
- But we can detect coherent waves of enormous numbers of gravitons, using detectors like LIGO
- Detecting huge events like the merging of two black holes (in some observed cases, such mergers have blasted off a mass/energy equivalent to several times the mass of our Sun)
See: https://en.wikipedia.org/wiki/Graviton#Experimental_observation