Aglobal synthesis of Paleozoic sequence-stratigraphic data has led to new insights into the nature, amplitude, and causes of base-level changes for this era. A “modal mean” Paleozoic sealevel curve is proposed based on “reference districts” from around the world, corroborated with data from ancillary sections. Estimating the amplitude of sea-level changes in the Paleozoic involves two separate measures: 1) long-term envelope of the sealevel changes driven by long-term tectonic processes, and 2) shorter-term third- and higher-order eustatic sealevel changes driven by glacial and other, unknown, processes that can be widely documented.

For the long-term envelope, a consideration of the global continental flooding estimates with epeirogenic corrections, stacked regional sea-level data, and modeling results for mean age of the oceanic crust seem to yield consistent results. For the shorter-term eustatic changes, sea-level rise and fall estimates from “reference districts” for various time slices is considered the best approach. Reference districts are localities where tectonic quiescence prevailed and thus the “modal mean” signal is more likely to be preserved.

Nevertheless, accurate estimates of the magnitude of sea-level changes from

Cambrian-Ordovician sea-level changes. The time scale and standard and regional stages are modeled.

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stratigraphy remain a challenge. As for the causes of short-term sea-level changes, nearly 38% of the Paleozoic experienced some or significant glaciation and thus a glacio-eustatic cause can be invoked for those intervals. For the remaining time, when there is no known evidence of ice accumulation, the trigger for sea-level changes is as yet unknown and remains one of the major mysteries of the earth sciences.

Crozon Fieldtrip

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