SEQUENCE STRATIGRAPHIC CORRELATION OF THE EARLY WENLOCK (VISBY-SLITE SUCCESSION) ON GOTLAND, SWEDEN WITH EASTERN NORTH AMERICA: EVIDENCE FOR A COMPOSITE IREVIKEN EVENT

The coastal exposures and inland quarries of Gotland provide an unparalleled opportunity to investigate the complex stacking patterns of facies and carbon isotope values present within the late Telychian-Sheinwoodian Ireviken Event. Abrupt facies changes within the stratigraphic succession are coincident with abrupt changes in trend and offsets in values of C-isotopes. Composite sections generated for the Visby and Slite areas of Gotland provide an onshore-off shore transect.

Detailed comparison of the uppermost Telychian-Sheinwoodian interval in Gotland with mixed siliciclastic carbonate successions in the Appalachian and Michigan basins of eastern North America and elsewhere reveal striking similarities of sequence stratigraphy, suggesting eustatic/climatic controls. For example, the Sheinwoodian succession features four major reef growth episodes (upper Visby, Hogklint, Stavklint and Kappelshamnsviken); each of these occurs above reworked deposits, interpretable as early transgressive systems tracts, and extend upward into thinly bedded, argillaceous facies of the highstand. Each of these episodes appears to be nearly synchronous with reef/biohermal intervals in eastern North America. We infer that upward building of mounds occurred in distinct episodes in the early Wenlock, associated with deepening episodes. The combination of clear, initially shallow water and rising base level fostered growth of bioherms. Collectively, these patterns indicate that the destabilization of the carbon cycle during the Ireviken Event resulted in at least three closely spaced excursion episodes, each associated with a cycle of sea level fall and rise.