“…While the upper BSR is generally interpreted to represent the current BGHSZ, the origin of the lower BSR has remained controversial. Several interpretations have been proposed, such as a relic of a former position of the BGHSZ (Posewang and Mienert, 1999;Matsumoto et al, 2000;Foucher et al, 2002;Baba and Yamada, 2004;Bangs et al, 2005), a current equilibrium feature associated with layers of gas hydrates with distinct compositions (Posewang and Mienert, 1999;Andreassen et al, 2000), or the lower boundary of a transitional zone between gas hydrates and free gas (Baba and Yamada, 2004). Alternatively, other processes not associated with gas hydrates such as transition from opal-A to opal-CT may create a normal-polarity diagenesis-related BSR (Hein et al, 1978;Berndt et al, 2004).…”