The Laurentian Fan or Laurentian Abyss is an underwater depression off the eastern coast of Canada in the Atlantic Ocean.
[1] Not a trench, but more of an "underwater valley", it is estimated to be at most ~19,685 feet (3.7 miles; 6.0 km) in depth.
The Laurentian Fan is a product of glaciation and water currents from the Gulf of Saint Lawrence.
Towards the end of the 1980s, it was discovered unexpectedly that the fan is the site of hydrothermal vents with their own ecosystems functioning in the absence of sunlight.
These supported organisms such as vesicomyid and thyasirid clams, as well as marine gastropods and other epifauna similar to those found in hydrothermal and cold seep environments elsewhere.