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Why did shallow seaways cover parts of continents during the Jurassic Period?
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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.
During the Jurassic Period, shallow seaways covered parts of continents primarily due to rising sea levels that caused marine waters to transgress upon continental interiors.31
While it is difficult to correlate specific local changes to global sea level fluctuations due to significant tectonic activity during this time, geologists attribute these rises to two main factors:
- Thermal Expansion: The absence of major glaciations and polar ice caps meant that warmer global temperatures led to the thermal expansion of seawater, which increased the volume of the oceans.234
- Plate Tectonic Activity: Accelerated seafloor spreading resulted in the enlargement of ocean ridges. This process displaced enormous amounts of ocean water, forcing it to flood onto the landmasses.3
These marine incursions were not permanent; the seas advanced and retreated repeatedly throughout the Jurassic, leaving behind extensive sedimentary deposits such as sandstones, limestones, and shales across various continental regions.231