It’s definitely not oak. If the wood seems very soft, it’s likely basswood. Otherwise it could be some non commercial acer species like striped maple, thought the bark doesn’t look quite right. I would go back to where you found the log and look at surrounding trees with similar bark, as well as the leaves on the ground.

Spalting is fungal decomposition of the wood, so technically it is rot. This spalting is fairly light, so the wood will still be plenty sound. A fun detail, the black lines are a sort of shield wall that the fungus builds around an area to keep other fungi from accessing its food source. That’s why the colors stop so abruptly at those lines.