One approach to the problem is to carefully examine closely spaced outcrops all the way across the State. However, their conclusions about it have not always fit together. Black shale of this type is deposited in the deeper parts of a marine basin. Only fine mud reaches the area. Commonly, the deeper water in the basin also had a low level of oxygen.
Organic matter is one of the components that makes the shale black.
Tongues of black shale extend eastward from this main body. A number of black shale tongues lie right on top of other, shallower marine facies in more eastern sites. The upward change to black shale is sudden at these eastern sites. Therefore, we believe that the deeper basin environment expanded rapidly. Deposition of the black shale tongue would begin everywhere in the expanded basin at almost the same time.