Passive continental margins in the Australian region provide evidence of very extensive sedimentation and basement subsidence both before and after the time of continental breakup. Postbreakup sedimentation is largely marine, extends to deep water and follows an exponential or thermal cooling (concentration) accumulation pattern. Here, late stage prebreakup sedimentation occurs within faulted troughs or grabens, and is described as rift phase. All prebreakup sedimentation is non marine to shallow marine, and available vitrinite reflectance data suggests deposition in a relatively low heatflow environment. Continental crustal refraction velocities in the range 7.1 to 7.5 kms/sec. are observed beneath those margins studied, and the refractor rises markedly towards the continent-ocean boundary. The refractor is interpreted as the greenschist-amphibolite metamorphic facies boundary which has risen in response to increasing thermal conditions up until breakup time. A quantitative basement subsidence and palaeoheatflow model has been constructed in which a simple temperature anomaly deep within the lithosphere during the prebreakup period gives rise to the observed complex subsidence pattern plus low vitrinite reflectance values.