Deformations and Degasation in the Upper Part of the Sedimentary Section in the Western Passive Margin of the Chain Transform Fault (Equatorial Atlantic Region)

Seismoacoustic profiles along the western passive margin of the Chain transform fault made it possible to define anomalies in the wavefield within the upper sedimentary layers: abrupt loss of coherency, box folds, “flat” and “bright” acoustic spots, and thrust-type faults. These features are interpreted as signatures of the ascending fluid flow. The anomalies are localized in the transition zone between the Romanche and Chain transform faults, where negative Bouguer gravity anomalies are indicative of a reduced density in the upper mantle to a depth of several tens of kilometers. It is important to note that the sedimentary cover is less than 1000 m thick in these areas. Hence, the mud volcanism can be ruled out as a process for deep fluid ascent. Based on the total array of field data and theoretical prerequisites, the origin of the fluids is attributed to serpentinization. This process depends on the presence and activation of deep-seated fault systems within the intraplate setting. This fact explains the spatial correlation of the anomalies with the transform trough.