Complex sentence: During late Jurassic times, this was an archipelago at the edge of the Tethys Sea, which included placid lagoons that had limited access to the open sea, where salinity rose high enough that the resulting brine could not support life.
Split into simpler sentences: During late Jurassic times, this area was an archipelago at the edge of the Tethys Sea. This included placid lagoons that had limited access to the open sea and where salinity rose high enough that the resulting brine could not support life.