Abstract More than 15,000 line-km of new regional seismic reflection and refractiondata in the western Arctic Ocean provide insights into the tectonic andsedimentologic history of Canada Basin, permitting development of new geologicunderstanding in one of Earth's last frontiers. These new data support arotational opening model for southern Canada Basin. There is a central basementridge possibly representing an extinct spreading center with oceanic crustalvelocities and blocky basement morphology characteristic of spreading centrecrust surrounding this ridge. Basement elevation is lower in the south, mostlydue to sediment loading subsidence. The sedimentary succession is thickest inthe southern Beaufort Sea region, reaching more than 15 km, and generally thinsto the north and west. In the north, grabens and half-grabens are indicative ofextension. Alpha-Mendeleev Ridge is a large igneous province in northernAmerasia Basin, presumably emplaced synchronously with basin formation. Itoverprints most of northern Canada Basin structure. The seafloor andsedimentary succession of Canada Basin is remarkably flat-lying in its centralregion, with little bathymetric change over most of its extent. Reflectionsthat correlate over 100s of kms comprise most of the succession and on-lapbathymetric and basement highs. They are interpreted as representing depositsfrom unconfined turbidity current flows. Sediment distribution patterns reflectchanging source directions during the basin's history. Initially, probably lateCretaceous to Paleocene synrift sediments sourced from the Alaska andMackenzie-Beaufort margins. This unit shows a progressive series of onlapunconformities with a younging trend towards Alpha and Northwind ridges, likelya response to contemporaneous subsidence. Sediment source direction appeared toshift to the Canadian Arctic Archipelago margin for the Eocene and Oligocene, likely due to uplift of Arctic islands during the Eurekan Orogeny. The finalstage of sedimentation appears to be from the Mackenzie-Beaufort region for theMiocene and Pliocene when drainage patterns shifted in the Yukon and Alaska tothe Mackenzie valley. Upturned reflections at onlap positions may indicatesyn-depositional subsidence. There is little evidence, at least at a regionalseismic data scale, of contemporaneous or post-depositional sediment reworking, suggesting little large-scale geostrophic or thermohaline-driven bottom currentactivity.