Aquatic sill

[5]An aquatic sill can be a biogeographic barrier for species between two basins, which commonly include sponges, bryozoans, bivalves, and cold-water corals.

These communities tend to develop in highly productive waters, such as upwelling areas, and build non-tropical reefs, or bioherms, around sills.

The sill is characterized by rocky seabed, low, muddy sedimentation, and accumulations of reef-forming cold water corals up to 40 metres (130 ft) thick.

[3] The gateway formed after the Messinian Crisis, 5.96–5.33 million years ago, when the Mediterranean Sea experienced a near-complete drought.

During the late Miocene and early Pliocene, a north-south-dominated tectonic stress field created pull-apart basins under a transtensional regime, thereby forming the gateway.