Ramps as modifiers of deformation of mass-transport deposits flow cells: A case study in the Santos Basin, SE Brazil

Mass-transport deposits (MTDs) are one of the several deepwater deposits and correspond to an important part of the gravitational sedimentation in the basins. MTDs register several pieces of evidence about their formation, which can indicate flow direction, level of internal deformation, and position in the deposit, for example. During the transport process, the flow can interact with the substrate and change its characteristics. Consequently, different structures are formed internally and in the basal surface according to the flow modification. In this study, 3D seismic data located in the northern Santos Basin was used to investigate the relationships between different MTD kinematic structures and styles of basal interaction. After conducting a comprehensive interpre-tation of the deposit, which involved morphological analysis, examination of basal and upper surfaces, and the assessment of internal facies distribution, we proceeded to correlate various structural elements, with the pur-pose of providing a clearer understanding of the sedimentation processes that took place within the deposit. On the basal surface, three distinct features (grooves, striations, and deformational elements) along with ramps, were interpreted. Apart from this, the distribution of large and small-size blocks, and normal and reverse faults within this MTD indicates that there were major changes in the flow behavior during the transport. Thus, we propose a model for the MTD transformation which considers ramp generation as a modifier of the MTD deformation and, consequently, as responsible for creating second-order flow cells, facilitating the substrate deformation, and providing erosive blocks near the flow base. In this model, the studied MTD was divided in five zones according to the nature of basal interaction. Typically, these zones are border by ramps. The variation in the internal structures suggest fluctuations in the flow velocity. Altogether, our findings indicate that the flow exhibited a compartmentalized behavior, giving rise to second-order flow cells.