I remember that in the case of the rounded, 65 million years, Chicxulub 170-180 km crater, there are scientists who believe that, because the perpendicular hit, the shockwave was so powerful that actually created in the opposite part of Earth, huge basaltic erruptions. At that time...India! Who was an island in her travel towards Asia. In a nutshell...Deccan Plateau. [en.wikipedia.org]
And let's not forget the Shiva crater! [en.wikipedia.org]
So, inspite of the fact that I don't believe your "craters" are connected with Clovis Impact Theory, maybe there are much older, and one way to figure it out is to look in opposite part of the world. The problem is how old and were are the basaltic floods(if they exist) because of the continental drift...
God is the only Simpsons character to have 5 fingers on each hand.