Studying fine-grained siliciclastic deposits of late Middle Devonian in the northern Appalachian Basin provides an exquisite natural laboratory to observe the complex environments in which mud can accumulate. More detailed correlation and facies characterization of this succession provide a wealth of information and insight into the diverse transport mechanisms responsible for distributing clastics hundreds of kilometers away from a tectonically active source area. Commencement of the third tectophase of the Acadian orogeny and a concurrent transgression is expressed throughout the region through the development of a basin-scale unconformity (the Taghanic Onlap) above a shelf collapse (i.e., Tully Limestone) and widespread deposition of organic-matter–rich mudstones. Deposition of the lower Genesee Group is believed to reflect the coupling of this local expression of a global eustatic highstand event and contemporaneous cratonic downwarping as a flexural response of the craton to a continent–microcontinent collision. High-resolution stratigraphy has allowed differentiation of genetically related packages, composed of distinct lithofacies, with characteristic physical, biological, and chemical attributes. The present paper advances an overview of this detailed investigation based on detailed core measurement and surface correlation to assess the controlling factors on the mid-Devonian stratigraphic fill of the northern Appalachian Basin and demonstrate the distribution in mudstone facies and their relation to changing environmental conditions.