Fig. 3.

Chemostratigraphy of the Lower Jurassic Fernie Formation from East Tributary of Bighorn Creek, Alberta and of the Lower Jurassic Posidonia Shale from the Dotternhausen Quarry in Germany; δ¹³C_org, organic carbon isotopic compositions from refs. 19 and 29; Fe_HR/Fe_T, amount of highly reactive iron relative to total iron; Fe_Py/Fe_HR, amount of pyrite iron relative to highly reactive iron (see SI Appendix for discussion of this redox proxy); ε²⁰⁵Tl, thallium isotopic composition of seawater during deposition. Lithostratigraphic members of the Fernie Formation, stages of the Jurassic, and ammonite zonations for both northwestern Europe and western North America are shown to the left of the stratigraphic column (refer to ref. 19 and SI Appendix for the details of their placements). Vertical gray lines in ²⁰⁵Tl records are the modern ²⁰⁵Tl_SW composition of ∼−6 (32). Light gray ε²⁰⁵Tl values in the German section are from lithologies that are not ideal for many metal isotope studies (total organic carbon values are less than 0.3%), and we therefore do not interpret these as primary oceanographic signals (SI Appendix). Gray boxes represent CIE intervals. Data from refs. 19 and 29.