https://www.lpi.usra.edu/planetary_news/202...n-an-early-sea/
Interesting concept in this being giant deposits of pumice. The currents of a possible ancient Mars ocean would favor any floating debris to be carried to the southwest of the volcano.
If true, apparently Olympus Mons has its guts all over the planet, thought a relatively small feat to Tooting crater supposedly throwing them all over neighboring planets.

There's a lot to like in this idea, but I wonder how the dates of the successive processes work out. Is Olympus Mons old enough (or the ocean recent enough)? I expect this is covered in the full paper. Perhaps someone with access can sketch the proposed chronology for us.

There is also a hypothesis that the MFF consists of vast piles of volcanic ash from all the Tharsis volcanoes and/or Apollinaris Mons, once forming a continuous belt around half or even more of the equator, now eroded into separate mounds. Mt. Sharp could be an outlier of the same material.

Phil

The main theory for years has been ash deposits from Apollinaris and Arsia/Pavonis. Like this new one, it has its support with climatological winds while raising further questions. I wish we could send a rover to the Mangala/Medusae area to check it out. It is geologically youthful either because it is recent or because it has been eroded overtime, erasing the craters.

Just out of interest, this image of a 200 square kilometre pumice raft was taken in the South Pacific in March 2020, arising from a small underwater fissure. If the Northern Ocean existed when the Tharsis bulge began to form the hypothesis on the Medusae Fossae Formation has some merit.

Looking at a topographic map of Mars, the Medusae Fossae looks like it is "truncated" near uniformly at around a kilometer below mean datum level from higher elevations to the south almost like a large "pumice iceberg" of material piled up against shoreline. https://www.researchgate.net/figure/Locatio..._fig2_327167111