"海相成因" can be translated into English as "marine origin" or "marine genesis".
"Marine origin" emphasizes that something (such as sedimentary rocks, minerals, or certain geological features) has its origin in a marine (sea) environment.
"Marine genesis" also conveys the idea of formation or origin in a marine context, with "genesis" often used in a more technical or scientific sense to refer to the beginning or formation of something.
In specific geological contexts, both terms can be appropriate depending on the nuance you want to convey.