Well-identified magnetic anomalies in the Caroline Basins define a sequence 28 to 38 m.y. old; reflection profiles show fracture-zone offsets on the Eauripik Rise, and narrow, broad topographic ridges help identify two abandoned spreading centers and several fossil trenches. A combination of these geophysical parameters supports an interpretation of the evolution of the region in two phases.
Two phases of sea-floor spreading are recognized in the East and West Caroline Basins. The West Caroline and Kiilsgaard troughs represent two disjointed segments of an extinct spreading center abandoned at 28 and 31 m.y. B.P., respectively. The spreading center then jumped into the Eauripik position and was active for the next 5 m.y.