During Alvin dives on the Laurentian Fan aimed at exploring the nature of the deposit of the 1929 Grand Banks earthquake and turbidity current, large, dense communities of living vesicomyid and thyasirid clams, gastropods, and other epifaunal taxa similar to those found in hydrothermal and cold seep environments were unexpectedly discovered. The communities are at 3800–3900 m in a passive margin setting, with no apparent mechanism for enhanced fluid flow. The communities occur near the crests of ‘gravel waves’, depositional bedforms created during the passage of the turbidity current, and on the slope and crest of a steep (20–30°) scarp of outcropping valley floor material. We speculate that these communities have established themselves since 1929 and that they are sustained by chemosynthetic processes. The reduced compounds fueling the chemosynthesis presumably are derived from older, organic-rich fan valley floor sediments that were exposed by the 1929 event.