Sea-Level Changes: Mechanisms, Magnitudes and Rates
Published:January 01, 1998
Sequence stratigraphy of third-order cycles is not determined by global eustasy but by local and regional tectonics interplaying with long-wavelength sea-level change. We can discern no mechanism that can cause the necessary short-wavelength, large-amplitude sea-level changes implicit in globally synchronous eustatic third-order cycles. Some mechanisms have the required amplitude but far too long a wavelength, some the necessary short wavelength but insufficient amplitude. Continental glaciation gives the correct amplitude/wavelength combination but did not operate for long periods of earth history. Much circular reasoning has been used to ‘establish’ eustatic third-order cycles. We believe that the magnitudes have been overestimated and that biostratigraphic correlation cannot be achieved to the necessary precision. The value of sequence stratigraphy lies not in its supposed relationship with global eustasy but as a basis for our understanding of basin dynamics. Long-term sea-level change is related to the episodic assembly, dismemberment and dispersal of supercontinents, which controls long-term sea-floor spreading rates, hydrography, climate, and the surficial geomorphic/stratigraphic evolution of the earth.
Figures & Tables
Paleogeographic Evolution and Non-Glacial Eustasy, Northern South America
Paleogeographic Evolution and Non-Glacial Eustasy Northern South America - Published eustatic cycle charts commonly call for eustatic fluctuations of more the 40 m every few million years or less. These cycles are interpreted as eustatic, but, so far, waxing and waning of continental glaciations is the only known mechanism which clearly has the ability to drive such large, short-term eustatic fluctuations. High-magnitude, high-frequency ?glacio-eustatic cyclicity? may be a valid concept for times of continental glaciations, but what about times when such glaciations was absent from Earth? Why do cycle charts have a similar form and style for time periods with and without glaciation? Is it that we have missed the identification of a fundamental driving cause which is as important as glaciation and which might have operated during non-glacial times? Or, is it that we are confusing local and eustatic drivers of relative sea-level change? These persistent questions, and others, continue to cast doubt on the entire subject of sequence correlatability. The papers in this book collectively address these questions.