Abstract

The Triassic-Jurassic (T-J) boundary has been located within the strata of the Sverdrup Basin through palynological analysis of both outcrop and subsurface sections. In the east the boundary occurs within the Fosheim Member of the Heiberg Formation, which consists mainly of delta-plain strata. In the west the boundary occurs within the marine shales and siltstones of the Grosvenor Island Formation. In all studied sections the boundary appears to be an unconformity which separates Rhaetian strata from Hettangian strata. The boundary is one of a number of low-order sequence boundaries which punctuate the Mesozoic succession of the basin with a frequency of 5-8 m.y. These data support the interpretation that the T-J boundary coincides with a global sequence boundary.

Palynological analysis indicates that the spore assemblage changes gradually throughout the Norian and Rhaetian and that a significant and relatively abrupt change occurs across the T-J boundary. The boundary is marked by the termination of common Norian-Rhaetian palynomorphs and by an influx of Jurassic bisaccates and the first appearance of typical Early Jurassic forms. These data support the hypothesis of a mass extinction at or very near the boundary, but the lack of detailed sample control precludes an interpretation of the suddenness (a few versus hundreds of thousands of years) of the extinction.

One explanation for the changes in the lithologic and paleontologic characteristics across the T-J boundary is that they were caused by short term environmental stresses (large bolide impact) which were superimposed on longer term stresses and base-level shifts associated with terrestrially-driven tectonic and eustatic changes.