INTEGRATED PALEONTOLOGIC, SEDIMENTOLOGIC, AND STABLE ISOTOPIC DATA ACROSS THE IREVIKEN AND LUNDGRENI EXTINCTION EVENTS IN THE CAPE PHILLIPS FORMATION, NUNAVUT, CANADA

Stratigraphic sections of the basinal Cape Phillips Formation, Nunavut, Canada, have been sampled across the Llandovery-Wenlock, and lower-upper Homerian (upper Wenlock) boundary intervals for the integration of paleontologic (graptolite, radiolarian, palynomorph), sedimentologic, and geochemical (¹³C) data for two well-known extinction events, the Ireviken and lundgreni Extinction (LEE) events. Graptolites are abundant and well-preserved, and provide a solid biostratigraphic base for other data. Graptolites were globally severely affected by both extinction events: about 80% reduction for the Ireviken, and 90-95% for the LEE. Recovery from the LEE was slow and diversity low through the late Homerian. Radiolarians, which are diverse, abundant, and beautifully preserved in the lower Homerian, are sharply reduced slightly below the LEE boundary. Upper Homerian data are more scattered, but diversity appears low with few radiolarian taxa surviving the LEE. Palynological studies are only preliminary, but it appears that chitinozoans were impacted by the LEE, briefly disappearing across the lower-upper Homerian boundary. Other rare palynomorphs, including prasinophytes and sphaeromorphs of varying preservation were recovered, but data are presently insufficient to determine the local impact of the LEE on these palynomorphs. Stable isotope geochemistry shows well-marked, positive excursions in the d¹³C_organic fraction associated with the Ireviken event and LEE. The Ireviken excursion (C1) curve has a sharp base, reaches a peak at about the Llandovery-Wenlock boundary, and tapers to the top of the centrifugus Zone. The LEE excursion (C4) peaks at, or slightly below, the lower-upper Homerian boundary. Both positive excursions appear to be close to, or coincident with regressions, particularly so across the LEE interval. The C4  excursion has a greater magnitude in the inshore sections relative to the offshore section, and is interpreted to be a result of accelerated weathering of carbonates exposed during a lowstand.