Source : Webster's Revised Unabridged Dictionary (1913)

Thalassic \Tha*las"sic\, a. [Gr. ? the sea.] (Geol.)
   Of or pertaining to the sea; -- sometimes applied to rocks
   formed from sediments deposited upon the sea bottom.

Source : WordNet®

thalassic
     adj : relating to the seas, especially smaller or inland seas;
           "deposits of sediment in gulfs and seas rather than in
           the ocean proper are known as thalassic deposits"-
           Scientific American