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How do Jurassic salt deposits and coal deposits provide clues about ancient rainfall?

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

In the study of the Jurassic Period, geologists use the distribution of specific sedimentary deposits to reconstruct ancient climate patterns:

Salt Deposits: Large deposits of evaporites—such as halite—serve as indicators of high aridity. These minerals form in environments where the rate of evaporation significantly exceeds the total water input from rainfall and river influx. Their presence suggests regions with high temperatures and low precipitation.12
Coal Deposits: Conversely, extensive coal deposits indicate areas characterized by high precipitation. Coal forms from the accumulation of organic plant matter in environments like swamps and bogs, which require consistent moisture to thrive and prevent the decomposition of organic material.13

By mapping these deposits, researchers have suggested that the Jurassic climate featured distinct regional variations, such as an arid belt on the western side of Pangea and more humid conditions in the east, likely influenced by the arrangement of large landmasses affecting wind and precipitation patterns.1