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

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 (Os-187/Os-188) is a suitable proxy for tracing hydrothermal activity associated with the LIPs formation, but Os-187/Os-188 data from the mid-Cretaceous are limited to short time intervals. Here we provide a continuous high-resolution marine Os-187/Os-188 record covering all mid-Cretaceous OAEs. Several OAEs (OAE1a, Wezel and Fallot events, and OAE2) correspond to unradiogenic Os-187/Os-188 shifts, suggesting that they were triggered by massive submarine volcanic episodes. However, minor OAEs (OAE1c and OAE1d), which do not show pronounced unradiogenic Os-187/Os-188 shifts, were likely caused by enhanced monsoonal activity. Because the subaerial LIPs volcanic episodes and Circum-Pacific volcanism correspond to the highest temperature and pCO(2) during the mid-Cretaceous, they may have caused the hot mid-Cretaceous climate. Mid-Cretaceous experienced a series of drastic environmental perturbations called Oceanic Anoxic Events. Here, the authors asses high-resolution Os isotopic records which indicate that most of these events were associated with massive submarine volcanic episodes, but some minor ones were not.

Automated summary

During the mid-Cretaceous, the Earth experienced drastic environmental perturbations, mainly triggered by submarine volcanic activities. High-resolution Os isotopic records indicate that most of these events were associated with massive submarine volcanic episodes, but some minor events may have been caused by monsoonal activity.