How many turbidity currents pass through a submarine channel during its lifespan?

Sediment-gravity flows coursing through submarine channels are the most important conveyors of sediment and organic carbon to submarine fans. Submarine channel deposits, therefore, should record the archive of this sediment transfer. However, channel deposits have often been considered to be dominated by erosion and bypass, and thus an incomplete archive. We present data from a millimeter-scale investigation of an outcropping submarine channel element in the Cretaceous Tres Pasos Formation, southern Chile that indicates that at least 520 sediment-gravity flow events passed through a single channel during its lifespan. These 520 events are confined by one primary channel-form surface and 11 secondary channel-form surfaces that define the channel architecture. Three facies (axis, margin, drape) compose this architecture, with thick, coarser-grained, amalgamated event-beds deposited in the axis, usually separated across secondary channel-form surfaces with thinner, finer-grained, non-amalgamated event bed s deposited in the margin. The drape facies usually overlies secondary channel-form surfaces, and we interpret its presence as an indication of significant sediment bypass through the channel. The 520 events are mostly preserved in the channel margin (82%), but the volumetric composition of the channel element is dominated by axis deposits (58%), with margin (37%) and drape (5%) being less significant. This indicates that the axis deposits, while the focus of many channel-related studies, only record a fraction of the temporal evolution of the channel. The channel margin, on the other hand, is the archive of turbidity current activity in the channel. Using reasonable event recurrence intervals and turbidity-current-event sediment volumes, we estimate that the studied channel was active for approximately 5,000 years with a total sediment load of 5.2 km3, with 4.5 km3 of sediment bypassing the channel downslope to a fan/lobe deposit. Both estimates of timing and volume compare well to age-constrained Quaternary submarine channels (e.g., Amazon, Zaire, Niger Y) and illustrate the importance of submarine channels as conveyors of sediment to the deep ocean sink.