news.scotsman.com/latestnews/Older-than-the-pyramids-buried.3883464.jp
Local plumber David Barnes saw the circular markings in the low afternoon light on Sandwick Bay. Julie Gibson, the county archaeologist, suggests it could come from a chambered tomb.
No picture at the link though, sadly.
A burn runs down to the Bay of Sandwick and there was a kirk and burial mound there. Near one side of the bay are the Nev Hill sites, a chambered tomb and a burial mound, on the other the Clouduhall cairn and standing stone. Weems Castle is a putative broch site falling into the sea. But the two concentric rings of this site remind me of phase ii of the mound on the southern end of the Ness of Brodgar, which archaeologists had also thought a broch [early antiquarians thought Kokna-Cummming more of a burnt mound]. How much more likely the highest waves in recent storms dislodged part of Weems Castle and the waves swept this RA to where it was found, rather than invoking some unseen sea-level site as an unhnown source for it to pop up out of.