Answer:
Shale is defined as a clastic sedimentary rock that is made up of clay particles that are very fine-grained in nature. This Clay results from the breaking down of feldspar minerals.
Shale generally forms in deep marine environment, lagoonal environment, lakes and swampy areas where the amount of water is sufficient for the accumulation of fine clay and silt size particles on the seafloor. These sediments after getting deposited is subjected to compaction and lithification as a result of which shales are formed.
Thus, it can be concluded that the environment of the formation of shales was a deep and shallow marine environment, lagoonal and swampy areas.
