Shale forms in low-energy environments where fine-grained sediment can settle and accumulate. These environments can include:

* Deep ocean basins: The slow currents and vast depths of the ocean floor allow fine clay and silt particles to settle out, forming layers of shale.

* Lakes: Similar to ocean basins, lakes can provide a quiet environment for shale formation, especially if they are deep and have limited inflow.

* Coastal lagoons: These protected areas, sheltered from strong currents, can accumulate fine sediments rich in organic matter, leading to shale formation.

* Floodplains: During floods, rivers deposit fine-grained sediments that can later compact and lithify into shale.

The specific environment and conditions that lead to shale formation influence its composition and characteristics.