Thanks everyone for your responses above.
The chick was unable to turn itself over onto its stomach when I found it this morning, and he was crying. Some yolk and umbilical gunk was still exposed from his abdomen. I moved him from the brooder (a tub under a heat lamp, where he had his own little nook behind some cardboard). His feet were still in fetal position. I stuck him under the butt feathers of my one currently broody hen, and he quieted down. I suspect though she will dispatch him at some point. I will let you know.
BTW he had black coloring on his legs, so I suspect he has some Araucana or Easter Egger, in addition to the Marans (from the dark shell).