PRE-GLACIAL NITROGEN CYCLE IN THE LATE ORDOVICIAN VININI FORMATION

The Late Ordovician is a time of extreme climate events. While most of the Ordovician climate was warm and equitable, the Late Ordovician culminated in a severe glaciation. The Vinini Formation in Central Nevada provides an excellent record of the Late Ordovician glacioeustatic events along the continental slope of Laurentia.

Denitrification in the oxygen-minimum zones along continental slopes of modern oceans plays an important role in the global N budget, and variation in rates of denitrification at the timescale of glaciations may represent an important forcing of global climate. Low δ¹⁵N values in the black shale unit of the Vinini Formation, ranging between +1 ‰ to -1‰, indicate nitrogen fixation and a lack of denitrification during the deposition of these deposits. This suggests that nitrogen denitrification might not have played a mayor role in controlling global climate dynamics in the Hirnantian.