Submarine sediment routing over a blocky mass-transport deposit in the Espírito Santo Basin, SE Brazil

Abstract

The control of slide blocks on slope depositional systems is investigated in a high-quality 3D seismic volume from the Espírito Santo Basin, SE Brazil. Seismic interpretation and statistical methods were used to understand the effect of differential compaction on strata proximal to the headwall of a blocky mass-transport deposit (MTD), where blocks are large and undisturbed (remnant), and in the distal part of this same deposit. The distal part contains smaller rafted blocks that moved and deformed with the MTD. Upon their emplacement, the positive topographic relief of blocks created a rugged seafloor, confining sediment pathways and creating accommodation space for slope sediment. In parallel, competent blocks resisted compaction more than the surrounding debrite matrix during early burial. This resulted in differential compaction between competent blocks and soft flanking strata, in a process that was able to maintain a rugged seafloor for >5 Ma after burial. Around the largest blocks, a cluster of striations associated with a submarine channel bypassed these obstructions on the slope and, as a result, reflects important deflection by blocks and compaction-related folds that were obstructing turbidite flows. Log-log graphs were made to compare the width and height of different stratigraphic elements; blocks, depocentres and channels. There is a strong correlation between the sizes of each element, but with each subsequent stage (block–depocentre–channel) displaying marked reductions in height. Blocky MTDs found on passive margins across the globe are likely to experience similar effects during early burial to those documented in this work.