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@hunter-thurmond – No, the Needmore formation is not equivalent to the Mahantango. However, they are very similar.
They USED to be part of the same group. Now, the Mahantango is part of the Hamilton group, while the Needmore shale is part of the Onondaga Group.
Looking at the stratigraphy, the Magantango is on the top, the Marcellus shale is in the middle, and the Needmore is below the Marcellus. (I attached a picture of the stratigraphy.)
The Magantango is a few million years younger than the Needmore. Also, the depositional environment was a little bit different, as the Needmore is composed of soft oily gray calcareous shale, while the Magantango is composed of siltstones and sandstones.
With that said, they are of similar age, and they do have similar fossils.