The Salinian orogeny is a major event recognized throughout the northeastern Appalachians. In  the northeastern Gaspé belt rocks, previous sedimentological analysis suggested that the Salinian unconformity was related to regional synsedimentary normal faulting during Late Silurian-Early Devonian. Within-plate volcanism in the Gaspé belt basin also occurred during this time interval. Even though these events strongly suggest that regional extension occurred during the Late Silurian-Early Devonian, brittle structures (fractures and faults) attributable to this event have never been recognized within the Gaspé sequences.

         A new approach, combining microstructural and microgeochemical studies was used to document the development of fractures during the Salinian event within the Upper Ordovician-Lower Silurian White Head Fm in northeastern Gaspé. Field and laboratory work was performed to determine chronological relationships between different microstructures and to define the progressive deformation history of the rocks. Petrography and isotope geochemistry were used to verify if the microfractures were enhanced by potential Salinian karsting. Samples from outcrops stratigraphically 200 to 1000 meters below the Salinian unconformity helped identify five sets of structures within the White Head Fm. They include bedding-parallel stylolites (T1); irregular dissolution planes and microfractures (T2), V-shaped veins (T3); subhorizontal veins and subvertical stylolites (T4); and subvertical veins (T5). d¹³C and d¹⁸O_VPDB of primary pore cement and vein calcites indicate that the general diagenetic trend for the White Head Fm evolves from marine conditions (d¹³C=0.5; d¹⁸O=-4.5‰), to progressively deeper burial conditions (d¹³C=0.2; d¹⁸O=-9.7‰). However at two sites, following a period of burial, the formation was subjected to shallower conditions during T3 (d¹³C=-1.0; d¹⁸O=-3.5‰). Cross-cutting relationships indicate that structures formed during T2-T3 events are post-lithification (T1) and pre-Acadian, because T4 and T5 are structurally compatible with the well-documented transpressional regime of the Gaspé Middle Devonian. T2 and T3 structures are brittle structures that imply shallow level P-T conditions, an interpretation which supports the isotopic indication. Results from fluid-inclusion microthermometry also suggest that rocks of the White Head Fm were buried, fractured, uplifted and then buried again. Thus, we conclude that T2 and T3 were brittle structures formed during a tectonic event of regional importance related to the Salinian disturbance.