Phanerozoic Eustasy

Isolation of the eustatic signal from the sedimentary record remains challenging, yet much progress is being made toward understanding the timing, magnitude, and rate of eustasy on both long-term (10⁷-10⁸ years) and short-term (10⁵-10⁶ years) scales throughout the Phanerozoic. Long-term eustasy is primarily driven by a number of factors relating to plate tectonics. The magnitude and rate of short-term eustatic change strongly suggests glacio-eustasy as the key driving mechanism, even in episodes of the Earth’s history often typified as having “greenhouse” climates. This notion is, in turn, supported by a growing body of both direct and proxy evidence for relatively substantial polar glaciation in many periods of the Earth’s history (with the possible exception of the Triassic). An understanding of eustasy is important for the development of the geologic time scale because it contributes to the sequence stratigraphic organization of sedimentary successions (including chronostratigraphic reference sections) and helps to understand the often incomplete nature of the geologic record. The integration of eustasy with our evolving knowledge of the Earth systems science (e.g., paleoclimate evolution, orbital forcing of sedimentary systems, geochemical evolution of the oceans, and biological evolutions and extinctions) will help to provide the tools to develop a context for the subdivisions of the geologic time scale.