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Interglacial high sea levels—an absolute chronology derived from shoreline elevations

1971; Elsevier BV; Volume: 9; Issue: 2 Linguagem: Inglês

10.1016/0031-0182(71)90034-4

1872-616X

W. T. Ward, Phyllis Ross, Donald J. Colquhoun,

Methane Hydrates and Related Phenomena

The heights of some stranded shores in Gippsland, Australia, greatly exceed the level to which the ocean would rise if all present-day ice were to melt, and uplift is thus implied. Differences in level shown by comparison of these interglacial shorelines with others in South Carolina may therefore be the result of movement of one area relative to the other. Contemporary shorelines in the two localities can nevertheless be recognized from certain physiographic similarities and from the meagre measured age data presently available. We believe, furthermore, that there is sufficient information to permit estimation of the average rate of relative movement, and we attempt to analyse the field observations by applying a simple model that relates shoreline elevation to implied rate of uplift. This model is based on the supposition that the earth movements actually experienced were continuous, or can be reasonably represented as small fluctuations about a regular long-term trend. use of the model permits estimation of absolute ages (calculated from differences in altitude of correlated levels) for each high sea level stage that is recognized. Although the calculated or “altimetric” ages derived in this way are quite speculative, they agree with radiometric ages of Alaskan transgressions, interglacial littoral faunas, and warm intervals identified in deep-sea cores, and seem therefore to be verified by these comparisons. Particular correlations between high sea levels and warm core stages are implied: if these pairings are accepted, the altimetric ages can be re-estimated using the ages of the core stages. Predictions which use the calculated ages also provide tests of their value. Study of the data from Gippsland and South Carolina, supplemented by observations from New Zealand, Mangaia (Cook Islands), Morocco and Lebanon, suggest that six high sea levels occurred in the last 250,000 years, and two about 400,000 years ago. Other stages of high sea level are dated at 0.76, 1.43, 1.66, and 1.97 million years. The occurrence of regular earth movements at coastal localities seems therefore to provide a means for dating sequences of marine terraces that span the entire Pleistocene. Application to the important Quaternary sequence of New Zealand suggests that the last three major glaciations experienced in that country occurred during the last 145,000 years. The implied rates of long-term earth movement relative to Mangaia are shown by comparison of shoreline elevations to be 2.40 ft. per thousand years for the West Coast of New Zealand, 0.214 ft. per thousand years for Gippsland, Australia, 0.073 ft. per thousand years for South Carolina and 0.059 ft. per thousand years for Morocco and Lebanon. These relative values for uplift become absolute rates if Mangaia has been free of earth movements in Quaternary times as the observations suggest.