The variably elongated and slot-like morphology as well as the crude alignment of organic pores in samples from wells on the anticline forelimb suggest that the organic pores collapse under tectonic deformation. However, samples with a constant TOC or clay mineral content exhibited lower bulk porosity in wells located on the forelimb than in wells located on the crest and backlimb of the overthrust anticline. The content of both total organic carbon (TOC) and clay mineral was correlated with bulk porosity, indicating the relevance and impact of both organic and inorganic pores on bulk porosity. The study encompassed mineralogical composition, petrography, and porosity, along with the state of tectonic stress and pore pressure in the Wufeng-Longmaxi shale of a basement-involved fold-thrust belt located in the southern Sichuan Basin. A systematic comparative analysis was conducted in the Changning area to detect the tectonic deformation of organic-rich shale.

Pore evolution in organic-rich shale is widely reported to be related to thermodynamic reactions, but its connection with tectonic deformation is overlooked. The regional Upper Devonian stratigraphy of western New York state indicates that the onset of overpressure occurred at a depth of ∼1100 m, well in advance of the Rhinestreet shale's entry into the oil window during the Alleghanian orogeny. Early and relatively shallow overpressuring of the Rhinestreet shale likely originated by disequilibrium compaction induced by a marked increase in sedimentation rate in the latter half of the Famennian stage (Late Devonian) as the Catskill Delta Complex prograded westward across the Appalachian Basin in response to Acadian tectonics. The depth at which the Rhinestreet shale became overpressured, the palaeo-fluid retention depth, was estimated by use of published normal compaction curves and empirical porosity-depth algorithms to fall between 8 m. The palaeoporosity of the Rhinestreet shale suggests that porosity reduction caused by normal gravitational compaction of the low-permeability carbonaceous sediment was arrested at some depth shy of its maximum burial depth by pore pressure in excess of hydrostatic. Compaction strain was recalculated to a palaeoporosity of 37.8%, in excess of that expected for burial >3 km. Analysis of differential gravitational compaction strain of the organic-rich shale around embedded carbonate concretions that formed within a metre or so of the seafloor indicates that the Rhinestreet shale was compacted ∼58%. These overpressure events were thermal in origin and induced by the generation of hydrocarbons during the Alleghanian orogeny close to or at the Rhinestreet's ∼3.1 km maximum burial depth. The Upper Devonian Rhinestreet black shale of the western New York state region of the Appalachian Basin has experienced multiple episodes of overpressure generation manifested by at least two sets of natural hydraulic fractures.

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