Within the American moral system there are many explicit separate moral systems. I do not think the divergence is very great, or we could not sit on juries together as readily as we do.
I do not think that our moral system is directly connected to our religious heritage. It is distinctly American.
Let me suggest what this moral system is.
We Americans have morals built around a simple proposition: a child is born with the right to fully develop his or her best qualities, skills and talents. Society must have a parallel moral system that supports this simple proposition.
This is why we so fervently support meritocracy. We are outraged that anyone should benefit from their family birth. Hereditary advantages are viewed as offensive. We fervently support learning opportunity equally for everyone. We fervently believe in scholarships and subsidies for the talented.
We abhor and punish insider trading that keeps legitimate people out of the loop. We abhor people, products and services that mislead individuals. Those individuals have a right to the best knowledge and skills to develop their own lives.
I do not need to go further. I think most of my readers will agree that these are fundamental American moral precepts. They are much more important and universal than issues of monogamy, church attendance or charitable giving.
As far as I can tell there is no particular book or article that summarizes the American moral system that I have just outlined. The closest I know is Charles Taylor's The Ethics of Authenticity.
It is also evident that American morals, because they support everything that enhances the individual's opportunities to develop their full capacity, includes environments that promote diversity as a moral value, meritocracy and openness. The values that help commerce to thrive.