I'm not real qualified to answer you but your dirt might be similar to mine. Most ponds here hold water well. I have seven ponds dug by someone else (one is a dairy lagoon and one ins a cooling pond for cows) and I have dug two and deepened out a third. Two of the ones dug by someone else and the one I deepened were not constructed properly. You can see that they didn't move the black topsoil away or core the dam first. They leaked slowly.
With such good soils in your area you probably just have to make sure that you move the black dirt away first before you start the dam and compact it some with the dozer.
What I did with my ponds was move the black dirt and then when I started the dam I built it toward the hole so the top of my dam went straight up instead of the top getting farther from the hole. Does that make sense?
In the pond that I dug deeper, you could clearly see that the dozer guy pushed the clay up, over, and behind what he previously just pushed and it left a black seem. I put about two foot of clay on top of that seam which essentially moved the dam in. I have yet to get enough rain to see results.
As far as the rock, two of my ponds have rock bottom and even if there are cracks, they are surrounded by the same clay that holds water.
I think you'll be okay but I can't guarantee it.