THE SUB-GUADALUPIAN (SUB-MIDDLE PERMIAN) UNCONFORMITY IN ARCTIC CANADA AND ALONG NW PANGEA: A MAJOR PLATE REORGANIZATION LINKED TO THE URALIAN OROGENY

One of the most significant unconformities of the Carboniferous to Triassic succession of the Sverdrup Basin, Arctic Canada, is the sub-Guadalupian (sub-Roadian) unconformity. It is a major reflector on seismic profiles, a sharp erosion surface that is also easily recognizable in the spectacular outcrops of Ellesmere and Axel Heiberg islands. The unconformity is locally angular, indicating differential uplift, block rotation and exhumation of half-grabens that had developed during an earlier Mississippian to Early Pennsylvanian rifting phase. Subsequent regional crustal collapse led to a widespread Roadian transgression that coincides with the establishment a new sedimentary regime across the basin, one that was dominated by heterozoan carbonate and biosiliceous chert accompanied by a pronounced clastic influx. In the Sverdrup Basin, the unconformity post-dates Early Permian inversion tectonics and magmatic arc plutonism evidenced by structural relationships and zircon geochronology. The sub-Roadian unconformity and subsequent collapse represents a tectonic event that affected the entire NW margin of Pangea. In the Barents Sea and Svalbard, it coincides with the deposition of the Kapp Starostin Formation. In Arctic Alaska, it marks the onset of Sadlerochit sedimentation. In western Canada, it heralds the onset of chert dominated sedimentation represented by the Fantasque and Ranger Canyon formations. In the western USA, it marks the depositional onset of the Phosphoria Formation. In all these areas, the unconformity marks the end of fault-controlled subsidence and establishment of a regime of passive subsidence. The unconformity thus marks the end of compressional tectonics all along NW Pangea. These tectonic events can be tied to the final consolidation of Pangea and a contemporaneous plate reorganization linked to the Uralian Orogeny, as Kazakhstan and Siberia sutured with the already amalgamated Laurussia and Gondwana. Tectonism resumed along NW Pangea briefly around the Permian-Triassic boundary, as evidenced by the Sonoma Orogeny in the USA and contemporaneous tectonic uplifts in the Sverdrup Basin and Barents Sea, likely contemporaneous with a final Uralian push.