Isopycnic

An isopycnic surface is a surface of constant density inside a fluid. An isopycnic surface is a surface of constant density inside a fluid. In geology, Isopycnic surfaces occur especially in connection with cratons which are very old geologic formations at the core of the continents, little affected by tectonic events. These formations are often known as shields or platforms. These formations are, relative to other lithospheric formations, cooler and less dense but much more isopycnic. Isopycnic surfaces contrast with isobaric or isothermal surfaces, which describe surfaces of constant pressure and constant temperature respectively. It is common in conversational use to hear isopycnic surfaces referred to simply as 'iso-density' surfaces, which while strictly incorrect, is nonetheless abundantly more clear.