EAGER: Do Mass Extinctions Have Diagenetic Consequences? Investigating Unique Early Diagenesis at the Triassic-Jurassic Boundary

University Of Southern California, Los Angeles CA

Investigators

Abstract

Do Mass Extinctions Have Diagenetic Consequences? Investigating Unique Early Diagenesis at the Triassic-Jurassic Boundary PI: David J. Bottjer Co-PI: Frank A. Corsetti EAR-1017536 ABSTRACT The geological process of diagenesis occurs when soft sediments are turned into hard rocks. Diagenetic features are commonly considered ?secondary features? because they occur after the sediments are buried, mostly isolated from surface conditions. As secondary features, they are usually overlooked when investigating ancient environments. In contrast, PIs recent discoveries suggest that diagenetic processes operating at or just below the seafloor during the time of a mass extinction may indeed hold previously unnoticed clues to the causes of mass extinctions. PIs have discovered unique diagenetic features?calcium carbonate fan layers?associated with the Triassic-Jurassic (T-J) boundary, one of the ?Big 5? mass extinctions, in eastern British Columbia. Textural and geochemical evidence suggests that the calcium carbonate layers grew immediately below the seafloor, likely influenced by ocean chemistry at the time of the mass extinction. Carbon isotopic analysis coupled with mass balance calculations suggest dissolution of preexisting carbonate likely provided the source of calcium carbonate for the early diagenetic layers, potentially indicating ocean acidification in their formation and as a potential extinction mechanism. Here, PIs propose the novel concept that mass extinction mechanisms could affect the diagenetic realm and that studying long-ignored diagenetic features might elucidate the extinction mechanisms in ways not previously exploited. Intriguingly, a literature search turned up unusual carbonate diagenetic features at other T-J boundary sites from around the world, but their nature and occurrence with respect to the extinction is unclear. To determine whether the features are relevant to the extinction, PIs propose a pilot study to investigate unusual diagenetic phases found elsewhere (e.g., St. Audrie?s Bay, England; Lavernock Point, Wales; and Larne, Northern Ireland) within their emerging framework of extinction-related diagenetic effects. The discovery that the carbonate diagenetic features from multiple localities are indeed relevant to the extinction will provide the impetus for a subsequent full-scale study of numerous other T-J sites to exploit a new window?the early diagenetic realm?in the study of mass extinctions.