If I'm not mistaken, the reason there's no treaty is that the indigenous people did not entertain the concept of sovereignty. There was no one to sign a treaty.
Sovereignty is the supreme authority within a territory. Sovereignty entails hierarchy within the state, as well as external autonomy for states. In any state, sovereignty is assigned to the person, body, or institution that has the ultimate authority over other people in order to establish a law or change an existing law.