Sediment redistribution processes in Baffin Island fjords

Abstract

Four decades of studies on pristine Baffin Island fjords are summarized with respect to sediment redistribution processes and resulting deposits. Sediment fill in these fjords occurred during the Holocene epoch , when deglacial and postglacial processes led to sandy-mud basin fills. The sand component mostly enters the fjord basins from fjordhead sandurs and their shoreline chute failures, triggering the release of yearly turbidity currents . These currents can travel long distances, often within leveed channels, leaving behind a seafloor of migrating cyclic steps that eventually transform into unconfined sediment waves . Channelized cyclic steps migrate upstream at up to tens of meters per year whereas unconfined finer-grained sediment waves migrate at much lower rates. Moored instruments and sediment traps in two fjords show turbidity currents to occur mostly in June through August when meltwater supply from glaciers is at a maximum. Not surprisingly, moored instruments were dragged downslope by turbidity current impact, suggesting high-concentration of suspended sediment within a thin near-bed layer. In rarer cases, large debris flows form even larger and longer submarine channels that carry sediment for tens of kilometers into the deep basin. These slide-generated debris flows can reorganize the basin floor as a sediment conduit for follow-on turbidity currents across thousands of years. Whereas sand is transferred to the deeper basin by turbidity currents, mud accumulates on the steep sidewall slopes and in the deep basin. Where mud accumulates on steep (≥13°) margins, many sidewall failures occur. Notably, right-hand margins contain a thicker sediment package and are affected by more sidewall failures than the left-hand side, primarily due to the Coriolis effect on increasing sediment accumulation rates. Of the many sidewall slope failures documented in Baffin Island fiords, iceberg collision with the seafloor is the only triggering mechanism directly observed. The association between subaerial debris flow fans and margin failures indicates that rock avalanches and subaerial debris flows also play a key role in triggering sidewall failures. The active seismic zone along Baffin Bay, likely initiated the rare but large deep-seated landslides observed in the sedimentary record. Baffin Island fjords are incredibly dynamic coastal environments with an ability to annually redistribute large masses of submarine sediment.

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