During the Oligocene and early Miocene, large swathes of Patagonia were subject to a marine transgression, which might have temporarily linked the Pacific and Atlantic Oceans, as inferred from the findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation.[26][27] Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography.[26][28] The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction.