KUNGURIAN TO LOPINGIAN CORRELATIONS ALONG WESTERN PANGEA

Kungurian to Lopingian correlations along the Pangea western margin from the Delaware to the Sverdrup basins cannot be achieved by biostratigraphy alone. Correlation requires the integration of biostratigraphy, sequence stratigraphy, paleoecology and evolution models because major sea-level fluctuation and climatic changes affected conodont distribution and morphology. The GSSP for the Kungurian-Guadalupian boundary is located in West Texas where smooth neogondolellids represented by Mesogondolella idahoensis lamberti disappeared and serrated neogondolellids represented by Jinogondolella nankingensis nankingensis evolved. This rapid, punctuated change was associated with a major transgression that can be recognized along the Pangea western margin in the lower Meade Peak of the Phosphoria Basin and in the lower Assistance Formation of the Sverdrup Basin. Temperature gradients along this margin are reflected by conodont clines; in the latter two regions the boundary is recognized by the transition from M. idahoensis idahoensis to J. nankingensis gracilis. This serrated biome was very short-lived in the Sverdrup Basin; cold-water environments, smooth biome and very gradual morphologic evolution of Mesogondolella species represent the rest of the Guadalupian and Lopingian. In contrast, several species of Jinogondolella, recognized by gradational morphologic changes, define zones within the Delaware Basin during the Guadalupian. The Phosphoria Basin includes mostly smooth forms, but occasional and rare serration may indicate some gene flow between the two biomes that could provide a means for correlation. Two major Guadalupian sequences can be recognized in the Sverdrup Basin where a major unconformity within the Trold Fiord Formation may approximate the Wordian-Capitanian sequence boundary. In West Texas the Guadalupian ends with a major sequence boundary terminating the Delaware Basin. Only evaporative facies of the Tessey and Castile may correlate with the beginning of the Lopingian. In the Sverdrup Basin, a distinct post-Guadalupian sequence within the Lindstrom Formation includes M. rosenkrantzi, M. aff. sheni, and M. sheni that may reflect gradual changes in a cold-water Lopingian succession, but interregional correlation is problematic.