Which layer in figure 4-1 forms the cap rock for the oil trap?

I am pretty sure that the layer in figure 4-1 which forms the cap rock for the oil trap is the layer  F that shows an example of stratigraphic traps that includes unconformity, lens, pinch-out in which you can see how the oil is stuck inside the porosity of the rocks. 
Do hope you will find it helpful! Regards.

The type of rock she find is a sediment rock