Mid-Cretaceous marine Os isotope evidence for heterogeneous cause of oceanic anoxic events

Hironao Matsumoto,Jairo F Savian,Ricardo Trindade,Kotaro Shirai,Junichiro Kuroda,Rodolfo Coccioni,Luigi Jovane,Fabrizio Frontalini

doi:10.1038/s41467-021-27817-0

Abstract

During the mid-Cretaceous, the Earth experienced several environmental perturbations, including an extremely warm climate and Oceanic Anoxic Events (OAEs). Submarine volcanic episodes associated with formation of large igneous provinces (LIPs) may have triggered these perturbations. The osmium isotopic ratio (187Os/188Os) is a suitable proxy for tracing hydrothermal activity associated with the LIPs formation, but 187Os/188Os data from the mid-Cretaceous are limited to short time intervals. Here we provide a continuous high-resolution marine 187Os/188Os record covering all mid-Cretaceous OAEs. Several OAEs (OAE1a, Wezel and Fallot events, and OAE2) correspond to unradiogenic 187Os/188Os shifts, suggesting that they were triggered by massive submarine volcanic episodes. However, minor OAEs (OAE1c and OAE1d), which do not show pronounced unradiogenic 187Os/188Os shifts, were likely caused by enhanced monsoonal activity. Because the subaerial LIPs volcanic episodes and Circum-Pacific volcanism correspond to the highest temperature and pCO2 during the mid-Cretaceous, they may have caused the hot mid-Cretaceous climate.

Highlights

During the mid-Cretaceous, the Earth experienced several environmental perturbations, including an extremely warm climate and Oceanic Anoxic Events (OAEs)
From the Os isotopic variations, we found that midCretaceous OAEs can be classified into two types according to their triggering factors as: (1) volcanic-induced OAEs (e.g., OAE1a, Wezel Level, Fallot Level, and OAE2) with unradiogenic Os isotopic shifts; and (2) monsoon-induced OAEs (OAE1c and OAE1d) without unradiogenic Os isotopic shifts
The upper Barremian of the composite record belongs to the Maiolica Formation and consists of white cherty limestone cyclically intercalated with thin (~few centimeters) black shale layers[8]

Summary

Introduction

During the mid-Cretaceous, the Earth experienced several environmental perturbations, including an extremely warm climate and Oceanic Anoxic Events (OAEs). The warm climate during the mid-Cretaceous is considered to have been sustained by a high pCO2 (e.g., ~1500 ppmv during the Cenomanian6) derived from active outgassing associated with the production of oceanic crust and/or massive volcanic activity[7]. This greenhouse world experienced distinctive repeated oceanic anoxic events (OAEs), representing major perturbations in the carbon cycle characterized by deposition of organic-rich sediments in various depositional settings. Massive volcanic events associated with the formation of large basaltic plateaus called large igneous provinces (LIPs) are the most probable triggering factors of environmental perturbations[15]. The Os isotopic record from the mid-Cretaceous is limited to the latest Barremian to early Albian and Cenomanian–Turonian transitional intervals[13,16,19,20,21], and these records are not sufficiently long to elucidate the evolution of the prolonged hydrothermal activity associated with volcanic episodes during the mid-Cretaceous

Methods

Results

Conclusion