Abrupt global-ocean anoxia during the Late Ordovician-early Silurian detected using uranium isotopes of marine carbonates.

ABSTRACT: Widespread marine anoxia is hypothesized as the trigger for the second pulse of the Late Ordovician (Hirnantian) mass extinction based on lithologic and geochemical proxies that record local bottom waters or porewaters. We test the anoxia hypothesis using δ²³⁸U values of marine limestones as a global seawater redox proxy. The δ²³⁸U trends at Anticosti Island, Canada, document an abrupt late Hirnantian ∼0.3‰ negative shift continuing through the early Silurian indicating more reducing seawater conditions. The lack of observed anoxic facies and no covariance among δ²³⁸U values and other local redox proxies suggests that the δ²³⁸U trends represent a global-ocean redox record. The Hirnantian ocean anoxic event (HOAE) onset is coincident with the exti

SUBMITTER: Bartlett R 

PROVIDER: S-EPMC6003337 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature