Studies of marine magnetic anomaly data from the Coral Sea basin reveal magnetic lineations which strike N70¿W almost parallel to the northern margin of the Queensland Plateau. The lineation pattern is best developed in the eastern part of the basin, and we can confidently identify a sequence of anomalies 26 (and perhaps 27) through 24 repeated about an extinct spreading center along the long axis of the basin. The extinct spreading center is associated with a short-wavelength (λ≲40 km) free air gravity anomaly low of 10--20 mGal and a region of rough acoustic basement. We infer that the Coral Sea basin began opening at about 62 m.y. B.P. at a half-spreading rate of 2.4 cm/yr and that spreading ceased at about 56 m.y. B.P. Although the Coral Sea ceased opening at the same time as the Tasman Sea, finite rotations determined for anomaly 26 lineations from these two basins are distinctly different. We thus infer that at least one additional plate boundary was active in the Paleocene and that it met the Coral Sea and Tasman Sea plate boundaries at a triple junction near the eastern end of the Coral Sea basin.