As a geologist, and looking at the photos, #3 seem to be stromatolites, the result of algal mound edifications. They end up lloking like bath tubs upside down. These algae have been doing this stuff for hundreds of millions of years, and keep doing it at present day.
In fact, Shark Bay in Australia is often cited as a modern day analogue for these things, where one can look at present day structures.
Nice lighting on the photos too!