Not Marin. Looks to be a fairly low end frame judging by the rack mounts, kick stand mount and dynamo bracket. Not worth a lot, would build into a heavy but solid bike
A quick weight will also reveal if it's worth saving. My guess is that's over 3.5kg...and therefore gas pipe. Such bikes can ride nicely though and make excellent transport.
A basic frame works ok - but if you festoon it with matching cheap components, it will break - so the value of a build kit worth using way exceeds the cost of a nice old frame