Tertiary sea levels in Australia and New Zealand

Abstract

Little is known of absolute Tertiary sea levels in Australia and New Zealand for periods prior to the Pliocene because of the widespread occurrence of earth movements, particularly in the Early and Middle Tertiary. Stratigraphic studies, however, reveal a sequence of large relative changes in land and sea level since Cretaceous times. Some of these changes are widely recorded, and there is evidence suggesting contemporary climatic changes. For these reasons it is believed that some of the changes in relative level of land and sea indicated by the sedimentary record represent, in part at least, real changes in level of the sea. In southwestern Victoria, two major Tertiary transgressional/regressional cycles can be found. The first is largely confined to the Paleocene. The second commenced in the Eocene and, with some reversals of direction, reached its culmination in the Miocene. In New Zealand, the record is inconclusive prior to the mid-Eocene, when the land was probably emergent. Subsequent transgression, recorded by sediments of Te Kuiti Group, continued to the end of the Oligocene and was interrupted in the Miocene by block-faulting. In the Pliocene, near stability seems to have been attained near Adelaide in Australia and in northern New Zealand, and sea levels in the Early Pliocene are believed to have been below the present. The later Pliocene record is one of rising sea levels; by the end of the period (the boundary to the Pleistocene being indicated by the incoming of cool-water faunas), sea level was substantially above its present position. Subsequent large changes in ocean level indicated by stratigraphic and geomorphic studies are attributed to the growth and decay of Pleistocene ice sheets, reinforced in part by presumed tectono-eustatic movements.