COMBINING MAGNETIC SUSCEPTIBILITY WITH TRADITIONAL LITHOSTRATIGRAPHY, BIOSTRATIGRAPHY, AND SEQUENCE STRATIGRAPHY TO IMPROVE THE STRATIGRAPHIC RESOLUTION OF UPPER DEVONIAN CARBONATES IN WESTERN CANADA

MISSLER, Rebecca J., Geology & Geophysics, University of Alaska Fairbanks, P.O. BOX 755780, Fairbanks, AK 99775-5780, [email protected] and WHALEN, Michael T., Geology & Geophysics, University of Alaska Fairbanks, Fairbanks, AK 99775-5780

The Frasnian-Famennian boundary represents one of the most significant biotic crises of the Phanerozoic and is well exposed in rock outcrops in Eastern British Columbia. These Upper Devonian carbonate platforms are also significant petroleum reservoirs with related basinal source rocks. Various causes for the demise of a wide range of benthic and primarily low-latitude stromatoporoid-coral reefs and pelagic organisms have been suggested but none have proven undisputable. In this project we combine litho-, bio-, sequence, and magnetic susceptibility stratigraphy to better understand the pattern and timing of platform (reservoir) development.

While carbonate platforms are able to keep up with most sea level change through aggradation and progradation, basinal settings generally lag behind due to a lack in sedimentation leaving a bypass or erosional margin in the rock record making stratigraphic correlation difficult. While biostratigraphy is used, it is not always helpful due to the lack of diagnostic conodont species in platform environments and the limited biostratigraphic resolution of stromatoporoids, rugose corals, or brachiopods. Clearly another technique is required in order to gain a better understanding of the depositional environments and the timing of events in the Late Devonian. Magnetic susceptibility stratigraphy provides a means to analyze the timing of depositional events in the Late Devonian to a higher degree of accuracy. With marine regressions comes an increase in erosion resulting in an influx of terrigenous material into the carbonate dominated areas. The continentally derived debris has a greater magnetic susceptibility than the dominantly diamagnetic carbonate material. By comparing the magnetic susceptibility signals from coeval locales we will be able to correlate across basins and with other basins around the world.

The combination of biostratigraphy, lithostratigraphy, sequence stratigraphy, and magnetic susceptibility will improve the stratigraphic resolution of carbonate platforms and in doing so will increase our understanding of the depositional environments, the timing of events, and the controls on source and reservoir rock deposition in the Late Devonian. This will also further our understanding into the pattern and timing of extinctions at the F-F boundary.