Chapter 9: A challenge: Is it possible to determine eustasy and does it matter?
Christopher G. St. C. Kendall, Philip Moore, Gregory Whittle, Robert Cannon, 1992. "Chapter 9: A challenge: Is it possible to determine eustasy and does it matter?", Eustasy: The Historical Ups and Downs of a Major Geological Concept, Robert H. Dott, Jr.
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An interest in eustasy, after a long dormancy, has been revived by the development of seismic stratigraphy. Eustatic events signal their occurrence through the synchronous creation or loss of worldwide accommodation of the space available for sediment fill. Such events can only be recognized if this signal is large enough, and of worldwide extent. The signal is dependent on reliable stratigraphic markers spaced sufficiently closely in time to resolve the sea-level events. The amplitude cannot be determined. Evidence for eustatic events are widely separated synchronous sedimentary sequences and the unconformities which bound these features.
To unequivocally interpret the stratigraphic record, one must be able to disentangle the effects of changing tectonics, eustasy, and sediment supply. In practice it is impossible to accomplish a complete calibration of seismic sequences, therefore it will always be a matter of interpretation. However, a wide range of geological characteristics place limits on tectonism and eustasy. This allows the application of a family of reasonable tectonic and eustatic models to explain basin history. In most instances, models within the family are similar enough to reproduce the stratigraphic record at the level of resolution produced by seismic sections. In many cases this is due to the fact that tectonics, eustasy, and sediment supply are linked, rather than being independent of each other. Hence, although absolute values of bathymetry and tectonics may never be determined with precision, models can generate complex basinal sequences with high fidelity using plausible inputs. Thus assumptions heaped on assumptions work.
Examples used to demonstrate the above paradigm are from the Mesozoic and Tertiary of the Bahamas, the Gulf Coast of the United States, and the South Carolina Coast; and the Permian of the Midland basin of Texas.