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Why did very thick ancient rock salt beds likely form in partly enclosed sea basins?
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salt dome
Figure 1: Interrelationships of salt structures (see text)
Very thick ancient rock salt beds likely formed in partly enclosed sea basins because these environments allowed for the sustained concentration of brines necessary for evaporite precipitation.12
The formation of these extensive deposits required specific conditions:
- Aridity: Evaporation rates had to exceed the rate of water replenishment from precipitation and inflow.12
- Basin Isolation: A barrier or sill on the seafloor at the basin's entrance prevented concentrated saline water from flowing back into the open ocean.13
- Replenishment: Periodic breaching of the barrier—caused by global sea-level changes or crustal downwarping—allowed fresh seawater to enter the basin. This replenished the volume of water available for evaporation, enabling the accumulation of inordinately thick, regionally extensive salt sequences over time.13
Because the evaporation of a large quantity of seawater yields only a small volume of salt, this "barred" basin model explains how such massive beds could accumulate in the geologic record.3