Arrangements of manganese nodules in rows and cellular networks decorate Miocene chalk surfaces stripped by erosion at depths of 2700-3000 m on the north flank of Carnegie Ridge, eastern equatorial Pacific. The patterns are interpreted as bedforms, similar to the transverse ribs and stone cells of fast, shallow rivers in appearance, but probably not in origin. The powerful currents responsible for shaping these deep-sea bedforms and adjacent fields of foraminiferal sand waves are believed to be density flows of Peru Basin water that episodically spills into the warmer Panama Basin. These thermohaline density currents cascade down their erosional valley with many of the characteristics and some of the geologic competence of channelled turbidity currents.

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