THE CASE FOR SCIENTIFIC DRILLING IN THE ALEUTIAN BASIN

The history of the Aleutian Basin (Bering Sea) is largely unconstrained due to a paucity of direct sampling combined with the sparsity and age of geophysical data. Since the Aleutian Arc and Basin formed simultaneously, the basin history constrains formation models for the Aleutian Arc and subduction zone. Aleutian Basin sediments also include a high-latitude record of Cenozoic greenhouse-icehouse climate transitions. Direct sampling by drilling to basement (IODP) is the only way to tightly constrain crustal age and basin tectonic history, and also provides opportunities to study a high latitude sediment record reaching at least as far back as the Eocene.

Aleutian Basin oceanic crust underlies 1-7 km of well-bedded sediment, largely inferred to be turbidites. 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 interpreted from 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.

IODP drilling on the basin margins (Exp. 323) recovered little sediment >5 Ma. The only drilling in the basin interior, DSDP 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 or older, but Site 190 penetrated only about half of the sediment column at that location.

Dating direct samples of igneous basement obtained from IODP drill cores is required to understand the history of the Aleutian Basin oceanic crust and distinguish between several models of basin formation. Drilling to basement also provides opportunities for acquiring direct samples to 1) examine the overlying sediments to expand the high latitude picture of Cenozoic climate transitions; 2) study the volcanic history of the Aleutian Arc from cored tephra layers, 3) constrain the opening(s) of the Bering Strait oceanic gateway; and 4) examine the microbiological history of the high latitude Pacific.