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How do unconformities provide evidence for changes in Cambrian sea level?

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Cambrian paleogeography — Cambrian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cambrian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

In the context of the Cambrian Period, unconformities—defined as interruptions in the deposition of sedimentary rock—serve as key geological evidence for fluctuations in sea level.12

Specifically, extensive unconformities are interpreted as indicators of a global drop in sea level, as these gaps in the stratigraphic record suggest periods where marine deposition ceased, likely due to the retreat of shallow seas from continental shelves. A notable example is the Hawke Bay event, where such unconformities appear in sectors of Laurentia and Baltica that border the Iapetus Ocean.2

These physical breaks in the rock layers often correlate with significant biological changes, such as the extinction or restricted geographic distribution of various trilobite groups and archaeocyathans, which were likely impacted by the loss of shallow-shelf habitats during these sea-level regressions. Conversely, periods of rising sea level are evidenced by the abrupt displacement of sedimentary environments, where shallow-water deposits are overlain by deeper-water sediments.21