Decoupling δ¹³C_carb and δ¹³C_org at the onset of the Ireviken Carbon Isotope Excursion: Δ¹³C and organic carbon burial (f_org) during a Silurian oceanic anoxic event

Highlights

• Clear demonstration of the scale of high-resolution sampling required for future studies of this and other events

• First paired demonstration of a negative δ¹³C_org excursion during rising δ¹³C_carb values at the onset of the Ireviken Event

• First continuous high-resolution record and calculation of Δ¹³C and f_org during a Silurian global carbon cycle perturbation

• Likely the highest resolution paired record of δ¹³C_carb and δ¹³C_org ever produced from a Paleozoic biogeochemical event

• Further demonstration of the Silurian Ireviken biogeochemical event as a potential Paleozoic Oceanic Anoxic Event

Abstract

Paired records of δ¹³C_carb and δ¹³C_org across the Llandovery-Wenlock boundary demonstrate asynchronous behavior during the onset of the Ireviken Biogeochemical Event (IBE). The extremely high-resolution data produced from the Altajme Core, drilled from Gotland, Sweden, capture a negative excursion in δ¹³C_org during the initiation of the Ireviken Extinction Event (IEE) and prior to the onset of the Ireviken positive δ¹³C_carb Excursion (ICIE). The record of carbon isotopic changes through this interval illustrate that both Δ¹³C (the difference between δ¹³C_carb and δ¹³C_org) as well as the relative flux of organic carbon burial (f_org) vary in unique ways and at different times during the progression of the IBE. Both process-oriented variables within the global carbon cycle (Δ¹³C and f_org) track a series of events that help to demonstrate potential causative mechanisms of both the extinction and carbon cycle perturbation. The sequence of events demonstrated here largely mirror the cascade of events that took place during the Cretaceous Oceanic Anoxic Event 2 (OAE2) and a detailed comparison between the two events is provided here for the first time. The unique insight into the IBE presented in this work results primarily from the novel, nearly Neogene-scale resolution of the paired isotope data, which demonstrates the critical importance of high-resolution chemostratigraphic research to evaluating ancient perturbations to the Earth-life system. Additional data sets of equal or greater resolution through this interval will be critical to evaluate the global synchroneity of these short-lived events during the IBE, and similar high-resolution studies of other Paleozoic biogeochemical events may shed light on potentially similar causative mechanisms.