Buried Pockmarks Associated With Listric Faults of Salt Minibasins (Espírito Santo, SE Brazil): Evidence for Local Hydrocarbon Escape Since the Miocene

Abstract

Buried pockmarks are features associated with fluid seepage through ancient seafloors. In this work, high-quality 3D seismic reflection and well data are used to investigate the geometry, distribution and significance of listric faults and associated pockmarks in a salt minibasin from offshore Espírito Santo, SE Brazil. The results show that six out of ten pockmarks interpreted in the study area have crescent, elliptical, or elongated shapes. They occur along the trace of listric faults and on their immediate hanging-wall blocks, with pockmarks' long axes being nearly parallel to the strike of the faults. The pockmarks are approximately 1300–6200 m long, 600–4000 m wide, 30–139 m deep, and buried 50 to 500 m below the modern seafloor. They can be divided into fault-strike (type I) and fault hanging-wall (type II) pockmarks based on their spatial relationships. Type I represents pockmarks developed along the trace of listric faults, which acted as fluid conduits. Type II pockmarks were developed away from fault traces on their hanging-wall blocks. Their occurrence near listric faults was controlled by multiple factors, including the relative depth, length, area, and maximum displacement of listric faults. In addition, listric faults below horizon H4—an Upper Paleogene unconformity—do not show pockmarks around them. Listric faults with greater length, area, and maximum displacements were more likely to form pockmarks. In conclusion, the studied pockmarks are evidence for local hydrocarbon escape occurring in the Espírito Santo Basin since the Miocene. The results presented here can be applied to other regions around the world prone to geohazards and where carbon and hydrogen storage solutions are being proposed.