Siblings

Did Norwegian relatives marry each other in the 1600s. I am finding some people that I think are ancestors, and when you look through it looks like they married people who are eithe r siblings or cousins. For instance on this link I can find an ancestor, and then they look like either siblings or cousins to other ancestors.http://records.ancestry.com/ole_ellingson_nordre_records.ashx?pid=53438224