Abstract

A Pliocene–Quaternary submarine channel system, influenced by localized mass wasting, is investigated using high-resolution 3D seismic data from offshore Espírito Santo Basin, SE Brazil. Three abandoned channels, a channel belt, and a mass-transport deposit (MTD) are recognized in the channel system in a confluence region confined by salt diapirs. In this confluence region, the cross-sectional area (CSA) of the channel system can be up to 1.2 km², i.e., 4 to 10 times larger than other parts of the study area. These significant changes in the architecture and morphology of the channel system resulted from the interaction between mass-wasting processes and turbidity flows. We postulate that a basal erosional scar created by mass-wasting processes was later filled with an MTD. This basal scar was then used as a preferential pathway for turbidity flows, which were captured by its headwall and lateral margins. The interpreted data show that the captured turbidity flows greatly widened the basal scar but caused only small modifications in scar height. This predominance of widening processes over channel incision occurred because part of the MTD in the basal scar was removed downslope by turbidity flows and replaced by channel-fill deposits. This paper shows that important flow-capture processes can predominate in channel-confluence regions of continental slopes. Basal scars can capture turbidity flows and facilitate flow channelization, which are key processes for submarine-channel initiation. Importantly, the replacement of MTDs by channel-fill deposits has profound implications for reservoir volumes and net-to-gross ratios in channel systems and partly depends on the properties of the turbidity flows, such as their erosive ability and frequency. The more erosive and frequent flows are captured by the basal scar, the larger is the accommodation space created for subsequent sand-prone turbidites.