EUSTATIC AND TECTONIC CONTROLS ON SHAPING THE BERINGIAN CONTINENTAL MARGIN, BERING SEA, USA

The Beringian margin is ideally suited for studying erosional and depositional responses to sea-level change, climate, and tectonics because the Bering shelf is vast (>800 km wide), lies within a high-latitude ocean basin, and hosts immense submarine canyons that incise deeply into it. We present new compilations of multibeam, backscatter, acoustic subbottom, and seismic reflection data from a portion of the Beringian margin, which image features related to sediment transport and erosion across the shelf-slope-basin transition. The first set of features consist of topographic salients in the continental slope. These elongate ramps are commonly bounded by faults and eroded on their flanks. Seismic data image their internal stratigraphy as sharp, coherent, parallel seismic reflections corresponding to Pleistocene–Holocene pelagic and hemipelagic sediments. The scoured flanks along these features are consistent with localized mass-transport failures and proximal debris flows, which plausibly may have been triggered by fault movement and fluid/gas escape. In addition to the ramps, we identified 54 erosional (?) depressions with ~4-km-diameter and up to 150-m-depth along the 200-km-long section of the study area. We interpret these features as resulting from erosive density currents cascading over the steep margin during eustatic lowstands. Their presence implies that glacial intervals importantly modulate Bering shelf erosion over glacial-interglacial cycles.

Previous work has hypothesized that submarine canyon incision occurred during the Pleistocene-Holocene. However, modeling of rock uplift driven by such surface lowering requires at least 500 meters of uplift, even in the case of a rigid crust. Such a flexural response provides a mechanism for fault movement and uplift along the Beringian margin recorded by the observed tilting of the slope prolongations. However, this tilting is far more localized and uplift is far more subtle than that required by Pleistocene-Holocene incision of the Beringian canyons. Thus, a significant fraction of the erosion of this margin (and canyons) must have occurred prior to the Pleistocene.