So many different ideas have been tossed out for this piece now. I thought perhaps some folks who aren’t in the Facebook group I regularly post in might have some clue to be able to narrow this down.
The tan-colored half seems to be two layers of diagonal lines stacked on top of one another in a crisscross pattern, creating the holes in between.
This is another Mississippian Coldwater Shale packstone from South Haven, MI.