I don't believe theists and reject their claims of theism.

[fr0d0]

Supernatural fits very well. Potentially natural supernatural, as you propose, doesn't.

What grounds can one rationally posit such an oxymoron? I don't just propose it doesn't, it is the default option. My question is how does one bridge the gap between no grounds for plausibility to attempting to justify it as potential?

Yours was the oxymoron I refer to. I have no idea how you justify it.
What is 'no grounds for plausibility'?

At one point the Sun rising was by definition a supernatural occurrence, that became understood as natural, and the turtle example I gave, absurd or not, would have served as a more possible explanation than invoking an explanation from that which is imaginatively possible, i.e. God.

A lack of accurate information on any physical phenomenon does nothing to inhibit an accurate assessment of purpose. You make the mistake of mixing an obsession to know how things happen with a religious statement of meaning.

We draw upon our rationalising abilities that a world we are able to rationalise made possible.

Agreed, my question still stands. From what position do you justify conjuring explanations that are not grounded in the world you rationalize and then attempt to claim they are in fact, rational?

If the question is, "Where did the universe come from?" At what point is it rational to throw out the world around us, and simply posit that The Universe was created?...rationally? That is to say, with good reason?

I don't justify any explanations that are not grounded in the world I rationalise. I claim nothing as 'fact'. That would be irrational.

The question of origins is weakly dealt with in religion. Because that is out of the scope of religion. Every point known and to be known of origins affirms a creator. Why? Because creation invokes the supernatural > that which never can be known. No gap invoked. Rather a subject change.