Oceanography vs Geology CoursesWatch
My advice would be to look at different unis that offer the same course and read through their modules and see what interests you. Because some unis specialise in other things for example, 1 might specialise in the chemistry side of geology whereas 1 might specialise in the physical side.
Both sciences are very broad, so you need know what you want to study. The environmental side, the biological/chemical side etc.
I've looked at Exeter's courses for an example. Their Oceanography course has modules of mainly natural process and ecology core modules and some maths and geology optional modules. Their Geology course has a lot of physical and chemistry geology core modules, and paleoclimate change, paleobiology, environmental geology and more as optional modules.