hello. Marín is a spanish surname. I found members of my very family since 1484, when at the final of Granada war,the Catholics kings reconquered Setenil (Cádiz)and Ronda (Málaga), and one Marín family establish in my town, five centuries ago. Before, there are Marín in the 13th century in Sevilla, etc. The origin of the surname isn´t sefardí, as you said, but christian from the north of Spain (Galicia and Cantabria), but its possible that some sefardies has this surname like other ones. Sorry for my english.