The type of energy possessed by a fluid above its base level is

Potential energy.

Explanation:

By the definition of potential energy we know that it is the energy possessed by the body by the virtue of its position. It is different from kinetic energy which is the virtue of the motion of a body.

Now formula of potential energy is:

PE = mgh

Where

PE = Potential energy

m = Mass of body

g = Acceleration due to gravity

Now imagine a container filled with water. Everyone knows that water is contained in form of tiny molecules which can be considered as layers on each other. Now the layers get higher and higher, each molecule on the higher layer is getting farther and farther from the base line of container.

Now according to formula of potential energy,

mass and acceleration due to gravity are same but height is increasing continuously, thus every molecule has greater potential energy comparing the molecule which belongs to the lower layer. In this way you can see that the only energy contained by the molecules of fluid at the higher level than the base is potential energy.

Now PE at base = mgh(1)

PE = at height = mg(h2)

since h2>h1

So magnitude of potential energy at the higher level will increase. So you can say that, above the base level, energy possessed by a fluid is Potential Energy.