Disentangling Diagenesis From the Rock Record: An Example From the PermoTriassic Wordie Creek Formation, East Greenland

The measurement of isotope ratios in sedimentary rocks deposited over geological time can provide key insights to past environmental change over important intervals in the past. However, it is important to be aware that secondary alteration can overprint the original isotopic records. We demonstrate this principle using high-resolution carbon, sulfur, and oxygen isotope measurements in organic carbon, pyrite, and carbonate minerals (dCorg, d Spyr, d SCAS, d Ccarb, and d Ocarb) and kerogen analyses (HI and OI) from the Wordie Creek Formation, East Greenland. These sediments were initially deposited across the Permo-Triassic transition, but as we will show, the carbonate record has been altered by interaction with meteoric water significantly after initial deposition. Comparison of the better preserved organic carbon and pyrite records with a proximal Permo-Triassic sequence reveals significant pyrite-sulfur isotope variability across the Permo-Triassic transition. This regional heterogeneity argues against basin-wide euxinia and instead suggests localized changes in sulfur fractionation in response to variations in organic carbon flux. This hypothesis can be used to explain seemingly inconsistent regional trends in other sulfur isotopes across the Permo-Triassic transition. Plain Language Summary Much of what is known about environmental change in the past has been determined through measuring the chemical properties of rocks. In this study, we demonstrate how those chemical properties may have been altered by processes occurring millions of years later. We show new chemical records from rocks deposited during across the Permo-Triassic boundary (the world’s largest mass extinction event) in East Greenland and discuss how some of the records have been altered by interaction with rain water millions of years after they were deposited. Finally, we talk about the records that have been unaffected by alteration, and what they imply for environmental changes occurring across the PermoTriassic boundary.