The fault escarpment

The eastern limit of the Infante D.Henrigue Basin is a steep, locally up to 65°, slope corresponding to the front of the "Marques de Pombal" Thrust. The fault scarp, trending N15E, has been mapped from the Chirp-sonar profiles. (Fig. 12). The lower part of the escarpment corresponds to the free face, characterized by the outcropping of the hanging block material. The slope sometime shows a step-like topography, with narrow terraces covered by a thin (less than lm) pelagic drape. The base of the scarp (slope break) is covered by a debris talus fan, filling and/or onlapping the lowest part of the basin (Fig. 13). Diffraction hyperbolae from the foot of the scarp make difficult to well constrain the limits of this talus. The debris talus is characterized by a rough ondulated topography, transparent acoustic facies, and a lenticular-wedge shape. Its thickness varies from 5 m up to 12 m. It has a good lateral continuity and extends up to 4 km away from the fault scarp. Chirp-sonar profiles show similar transparent lenticular bodies interstratified within the turbiditic sedimentary sequences. In this area three gravity cores have been acquired (BSC1, 2 and 6) to study this unit in order to have an age constrain for the deposition of most superficial debris deposit.

Figure 13: BS98. Cores BSC 2 and 1, with Chirp data.