Side-scan imagery and 3.5 kHz profiles in the Norway Basin reveal ∼3–4 × 104 km2 of sea floor covered by regularly spaced (500–2000 m), low-relief hummocks previously attributed to bottom currents. Extrapolating from nearby borehole data, I attribute these mound fields to gravitational (Rayleigh-Taylor) instabilities resulting from superposition of 50–100 m of thick Pliocene-Pleistocene, glacigenic (glacier-derived) sandy clays (density 1800 kg/m3) on a several-hundred-metre thickness of Miocene biosiliceous oozes having a density of 1300 kg/m3. This hypothesis predicts or explains similar hummock fields in many oceanic regions where such density inversions exist.

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