The Major Depositional and Tectonic Changes Across the Near-Base Rhaetian (latest Triassic) Sequence Boundary in the Sverdrup Basin, Arctic Canada

Ashton Embry¹ and Erik P. Johannessen^2
1GSC, Calgary, AB, Canada.
²Statoil, Stavanger, Norway.

The Mesozoic succession of Sverdrup Basin (Canadian Arctic Archipelago) is about 10 km thick. Six 1st order sequence boundaries occur at the base, within, and at the top of the succession. One of these 1st order boundaries is the near-base Rhaetian (very late Triassic) sequence boundary.

This sequence boundary marks a significant change in depositional regime. Throughout the Triassic, the Sverdrup Basin received sediment from the extensive Canadian and Greenland shield areas to the south and east and also from an enigmatic land area to the north called Crockerland. During the Norian, Crockerland was by far the main source region for the entire basin. Thick, shallow water sandstones prograded southwestwardly over slope and shelf shales in the eastern and central portions of the basin from a sediment input area in eastern Crockerland.

A relatively short-lived interval of tectonic uplift occurred near the Norian/Rhaetian boundary, exposing the basin flanks and resulting in the final progradation of the Norian sandstone. Following this, widespread subsidence occurred and the basin margins were submerged. During the subsequent regression in early Rhaetian, a huge supply of sediment came into the basin from the shield areas to the east and southeast. Crockerland contributed little if any sediment to the basin and was never again a notable source area for the Sverdrup Basin.

Another major change which occurred across the near-base Rhaetian sequence boundary was the demise of the Tanquary Arch, a large positive area in the northeastern portion of the basin. The final episode of uplift of the arch was at the end of the Norian and all post-Early Paleozoic strata were stripped from its crest. Following the base Rhaetian transgression, the Tanquary Arch ceased to be a tectonic entity.

It would seem that the major, tectonic episode at the Norian/Rhaetian boundary, which affected basins throughout the world, was generated by plate-tectonic processes likely driven by changes in the mantle. The global, plate reorganization at the Norian/Rhaetian boundary had a profound effect on the tectonic and sedimentary patterns of the Sverdrup Basin presumably through the creation of a new stress regime for the basin and the surrounding source regions.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.