Aleutian Basin Stratigraphy: What We Know, What We Think We Know, and What We Don't Know

The history of the sediment-filled Aleutian Basin (Bering Sea) is largely unconstrained due to a paucity of direct sampling combined with sparsity and age of geophysical data. Since the Aleutian Arc and Basin formed simultaneously, basin history constrains models for forming the arc and subduction zone. Aleutian Basin sediments are also thought to include a high-latitude record of Cenozoic greenhouse-icehouse climate transitions. Based on combined analysis of all available seismic lines, correlation with existing drill sites, and regional depositional knowledge, we propose an interpretation of Aleutian Basin depositional history that extends as far back as the Eocene.

Aleutian Basin oceanic crust underlies 1-7 km of well-bedded sediment, largely inferred to be turbidites based on sparse drilling data. Seismic reflection data show bed pinch-outs and individual beds often finer than seismic resolution (esp. in 1970's-80's legacy data). Debris flow facies and mass transport deposits are prevalent on the southern (Aleutian) and eastern (Beringian) margins. Diatomite is abundant, as described in DSDP Site 190, and shown by a bottom-simulating-reflector in seismic data associated with the Opal A/CT transition. Basin sediments likely also include ice-rafted debris and volcanic tephra, although neither has been described in detail.

Ages of the oldest Aleutian Basin stratigraphy and underlying crust remain unknown. IODP drilling on the basin margins (Exp. 323) recovered little sediment >5 Ma. The only drilling in the basin interior, Site 190, penetrated Holocene to Pliocene diatomaceous silt and clay, unconformably overlying a minimal recovery of middle Miocene mudstone. Sediments below those drilled at Site 190 are middle Miocene in age or older, but Site 190 penetrated only about half of the total sediment column at that location.

Unfortunately, much of the regional seismic data is legacy or single channel, precluding many geophysical analyses. A single Marcus G. Langseth cruise (MGL1111) provides high-fold multichannel seismic reflection data. Some correlation of sediment packages across the basin is possible, but specific unconformities are difficult to trace beyond the few multichannel lines. IODP drilling to basement is needed to advance our understanding of Aleutian Basin formation and evolution.