Your example with "for" doesn't really make sense. "Because of" is a much better choice.

In some older, more archaic writing, you'll often find something like, "he fell into the sea, for the storm was wild and fierce and he was unable to keep his balance." "For" in this case would mean "because." Maybe you encountered a similar usage? Either way, like others have already mentioned, "because of" would be the better option between the two examples you gave :)

My initial thought--without careful checking--is that FOR can mean BECAUSE (or SINCE), but not BECAUSE OF. Also, you can't say FOR OF. As I said, I didn't research this. So you should check elsewhere also.

because of = as a result of He fell into the sea because of the storm.