ROV study of a giant pockmark on the Gabon continental margin

A giant, 800-m wide pockmark, called Regab,
was discovered along the Equatorial African margin at
3160-m water depth and was explored by remote operated
vehicle (ROV) as part of the Zaiango (1998–2000)
and Biozaire (2001–2003) projects carried out conjointly
by TOTAL and a number of French research institutes.
A microbathymetric map obtained using the ROV sensors
shows that the pockmark actually consists of a
cluster of smaller pockmarks aligned N70 along a 15-m
deep depression. Methane was recorded all over the
pockmark, the highest values along the axis of the
depression where massive carbonate crusts and dense
seep communities were also found. Several faunal species
belong to the Vesicomyidae and Mytilidae bivalve
families, as well as to Siboglinidae (Vestimentifera)
tubeworms. Preliminary analyses confirm their association
with symbiotic bacteria, thus documenting their
dependence on fluid seeps. The pockmark appears to be
related to an infilled channel, visible on the seismic data
300 m below the seafloor, which may act as a reservoir
for biogenic fluids supplied to the trap from the surrounding
sediments.