Widespread elevated iridium in Upper Triassic\u2013Lower Jurassic strata of the Newark Supergroup: implications for use as an extinction marker

Lawrence H Tanner,John H Puffer,Frank T Kyte

doi:10.1038/s41598-020-76238-4

Abstract

Anomalous levels of iridium in sedimentary strata are associated with mass extinction events caused by impact events. In the case of the end-Triassic extinction event, the anomalies as well as the extinctions are linked to the eruption of the Central Atlantic Magmatic Province (CAMP) flood basalts. We report new data on concentrations of iridium in continental strata of the Fundy, Deerfield, Hartford and Newark basins, both above and below the oldest CAMP flows in these basins, that demonstrate that these anomalies are more common than previously known. We conclude that the enrichments were at least in some instances likely derived locally by concentration due to leaching directly from the lavas into sediments proximal to the CAMP flows due to post-eruptive hydrothermal activity. In other instances, the enrichments likely record the global fallout of aerosols and/or ash particles during the eruptions of the CAMP basalts. The common association of the highest levels of enrichment with organic matter suggests either redox control or stabilization by formation of organometallic complexes following post-eruptive redistribution. These findings demonstrate the importance of considering the distribution and magnitude of iridium anomalies in considering the source of the iridium and possible extinction mechanisms.

Highlights

The occurrence of iridium (Ir) in sediments surrounding paleontological event boundaries has long garnered interest for its potential in identifying bolide impact as a possible driver of mass extinction
A pronounced negative carbon-isotope excursion (CIE) that records a disturbance of the global carbon cycle has long been associated with the end-Triassic extinction (ETE) in the marine realm[20,21,22,23,24,25,26] and is identified from terrestrial Triassic–Jurassic boundary (TJB) sections[16,27]
The presence of a Late Triassic pollen assemblage in the lowest few meters of the Scots Bay Member proves that the TJB occurs above the NMB8

Summary

Introduction

The occurrence of iridium (Ir) in sediments surrounding paleontological event boundaries has long garnered interest for its potential in identifying bolide impact as a possible driver of mass extinction. The focus of attention in the study of the end-Triassic extinctions has been the environmental effects of the eruption of the flood basalts of the Central Atlantic Magmatic Province (CAMP). It is well-established that the products of the CAMP eruptions span the system boundary[6,7,8,9], with the majority of the total lava volume ejected during an initial eruptive episode prior to the paleontologically-defined TJB10,11. The horizon of Ir concentration was generally a carbonaceous shale with abundant trilete spores (the so-called “fern-spike”)[30,31] that coincided with

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