The puzzle of the Marlborogh City:

Unlike new modern types of corals that appeared in the Early Triassic and Devonian periods, the two coral atolls that are the main characteristic features of the Marlboro city archipelago are an exception due to their very young nature. It surprises many scientists that the atolls were able to achieve this degree of growth and aging within such a short time.


There are more interesting observations that are outright puzzling:

• The Silversand atoll (the smaller) has distinct volcanic subsidence characteristics, however, it has a high central peak (see Zion Island), pronounced outward radial formations (the four major islands, Dutch Fort, Goodhugh, Spade and Silversand, and eight smaller islands) and terraced patterns with submerged radial features pointing towards the center of the atoll so characteristic of Tycho-type impact craters(!) on the Moon
  
• the Scotch atoll has an impact crater characteristics, except that together with the Silversand atoll it lacks geological composition - no brecciated rock, no laminated or molten rocks, and no central peak
  
• both atolls are ellipses and their major axes have a common alignment along 15 degrees true north