Marin painting (that's the signature)

The work was conveyed via an antique shop in Norfolk about 10 years ago. On the back of the painting there is an original paper that indicates a purchaser in-between who resided in Richmond, Virginia. As I understood the story from the dealer, her uncle had an antique and fine art business in Greenwich Village; he moved to Richmond in his later life and eventually passed along (as he had always done fine art, American Brilliant Cut Glass and good Chinese pieces) the painting to her many years ago. It had sat in her business (along with so many other pieces, away from view, as she was not really as much into art sales at the end of her life). I bought it and held on to it.

You can see that the painting has a patina wash over it, even in my not-so-great photos. We had art curator research the piece and it is her belief that this is authentic of its period and also pinpoints it to the dark portraiture that Marin did in the year or so following the death of Stieglitz and his wife. There are only pictures of similar dark portraiture in Marin catalogs. This is a piece that is totally 180-out from what he normally painted, but not outside what he did in his early career and at the end of his life. The piece still stumps me. I only buy what I like and this portrait appealed to me for completely different reasons than its signature. I would like to know more about it.