Question

How can geologists use sequences of sedimentary rocks to tell where sea level was in the past on a passive continental margin, like North Carolina? How does the position of the shoreline change in a transgression vs. regression?

Answer 1

Geologists use sequences of sedimentary rocks to determine past sea levels. Different types of rock indicate different environments, e.g., deep water, beach, or coral reef. A transgression sees sea levels rise or land sink, moving the shoreline inland. In contrast, a regression involves falling sea levels or rising land, moving the shoreline seaward.

Step-by-step explanation:

Geologists can use sequences of sedimentary rocks as a historical record to determine past sea levels on passive continental margins like North Carolina. Each layer of sedimentary rock represents a particular period of time, with different rock types indicating different environments. For example, shale might indicate deep water, sandstone might signify a beach environment, and limestone might suggest a coral reef.

Transgression and regression refer to the movement of the shoreline relative to the continental margin. During a transgression, sea levels rise or the land sinks, so sedimentary deposits shift landward, moving the shoreline inland. In contrast, during a regression, sea levels fall or the land rises, causing the shoreline to move seaward.

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