A continental margin which is not also a plate margin. Such margins are also known as ‘aseismic margins’ or ‘Atlantic-type margins’ and are contrasted with active margins. Passive margins are characterized by rifted and rotated blocks of usually thick sedimentary sequences. These rocks are often highly prospective for oil and gas, with a variety of traps, including those related to the diapiric (see diapirism) rise of the rock salt formed during the initial separation of the continents.