(adj) relating to the seas, especially smaller or inland seas; - Scientific American, Example:deposits of sediment in gulfs and seas rather than in the ocean proper are known as thalassic deposits
The Collaborative International Dictionary of English (GCIDE) v.0.53 Collaborative International Dictionary (GCIDE)
a. [ Gr. qa`lassa the sea. ] (Geol.) Of or pertaining to the sea; -- sometimes applied to rocks formed from sediments deposited upon the sea bottom. [ 1913 Webster ]