Marine Ecological State-Shifts Following the Triassic–Jurassic Mass Extinction

Abstract

One of the most severe extinction events in Earth history, the Triassic–Jurassic extinction, struck against a backdrop of radical increases in atmospheric CO2and supercontinent breakup. This juxtaposition of first-order geophysical and biotic changes produced excellent case studies in Earth-Life Transitions. Recent recognition of a worldwide “carbonate gap” following the extinction has focused attention on causes, often invoked as eustacy or ocean acidification, but the ecology of the extinction aftermath remains poorly understood. Results from paleoecological studies on three separate Triassic–Jurassic records are presented and incorporated into regional depositional models. Examination of the Penarth Group of Great Britain reveals a widespread, laterally homogenous, level-bottom microbial stromatolite regime across the innermost ramp. The Sunrise Formation in Nevada, USA, was deposited during a biosiliceous (“glass”) regime dominated by demosponges across the inner ramp that lasted at least two million years. Investigations of the Pucará group in the central Andes of Peru revealed a demosponge-dominated level-bottom glass ramp with many similarities to the Nevada deposits, but offering broader regional extent and variation in recorded depositional settings. This suite of studies demonstrates state-shifts in marine ecological systems that also profoundly altered regional sedimentation regimes. The sponge-dominated systems produced glass ramp conditions instead of carbonate ramps, and indicate the importance of marine silica concentrations. The post-extinction changes in regional marine ecology demonstrate connectivity to changes in global climate and terrigenous weathering driven by global-scale geophysical processes.