TESTING GLOBAL CORRELATIONS IN THE JURASSIC TOARCIAN STAGE WITH U-PB ZIRCON AND CHEMOSTRATIGRAPHY

Toarcian sedimentary and igneous rocks have yielded a variety of ages that broadly suggested links between the Toarcian Anoxic Event, a marine extinction, and the Karoo-Ferrar flood basalt volcanism. However, these relationships have yet to be tested with precise dating methods. Also, it has been previously suggested by others that Toarcian chemostratigraphic changes are such that their correlation potential may perfectly complement the time resolution provided by biochronology. Regardless of unusually precise chronostratigraphic value, these chemostratigraphic records are non-unique and need to be confirmed with independent chronometers. As a first step toward such tests we present five new CA-TIMS U-Pb zircon ages that range from 182.9 ± 0.3 to 180.0 ± 0.3 Ma (weighted mean ²⁰⁶Pb/²³⁸U ages with two-sigma error) that are associated with a new δ¹³C carbonate profile from southern Peru. Preliminary ammonite data suggests that this mixed carbonate-siliciclastic unit in Peru spans much of the Toarcian Stage. The Peruvian δ¹³C carbonate trend shows similarities with those in Europe, North America, South America, and Japan. These new U-Pb zircon ages are comparable with previously published U-Pb zircon ages from tephra in fossiliferous sedimentary successions. Also, these new data suggest a more precise age for the Pliensbachian-Toarcian boundary and help establish global correlations among chemostratigraphic changes associated with the Toarcian.