In 1962, ice island Arlis II drifted over a portion of the southern half of the Siberia Basin. Depth recordings made between 81 degrees N, 170 degrees E and 82 degrees 30'N, 160 degrees E show that the ocean floor in this area is an abyssal plain at about 2,825 m depth dissected by several interplain channels. This abyssal plain, here called the Wrangel Abyssal Plain, is bounded on the north by Arlis Gap, which joins it with the Siberia Abyssal Plain at about 3,946 m depth. The Siberia Abyssal Plain occupies the northern half of the Siberia Basin. Seismic reflection profiles show that a prominent subbottom basement ridge exists in the vicinity of Arlis Gap. This ridge strikes in an approximately northwest direction and appears to connect with Alpha Ridge, which bounds the Siberia Basin on the east and north, and with Lomonosov Ridge, which bounds the Siberia Basin on the west. The seismic reflection profiles also show that at least 3.5 km of subhorizontal, stratified sediments underlie Wrangel Abyssal Plain south of the ridge. Each layer within these sediments appears to correspond to a fossil surface of Wrangel Abyssal Plain. This thick sequence of stratified sediments shows the influence of the Asian continent, which bounds the Siberia Basin on the south, on sedimentation within the Siberia Basin. Presumably the buried basement ridge forms a dam which has permitted the accumulation of a thick sequence of sediments under the higher-level Wrangel Abyssal Plain. Turbidity currents moving through Arlis Gap presumably carried the overflow of sediments from Wrangel Abyssal Plain into the lower-level Siberia Abyssal Plain. The structure of the sediments suggests that the Siberia Basin has been free from deformation during the deposition of the sediments, except for possible broad crustal down warping. A crustal model based on the water depth measurements, seismic reflection profiles, gravity measurements, and magnetic measurements yields a crustal thickness of 15 km south of the buried ridge and 22 km under the ridge measured from sea level.

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