T15 Understanding the Links between Life, Biogeochemical Cycles, and Environmental Feedbacks throughout the Mesozoic

Sunday, 22 September 2024
8:00 AM - 12:00 PM
207B

NEW CONSTRAINTS ON TRIASSIC TO JURASSIC ATMOSPHERIC GAS CONCENTRATIONS FROM FLUID INCLUSIONS IN SURFICIAL MINERALS

Paper number: T15-5
Program: Technical Sessions
Time: 8:55 AM – 9:10 AM

Authors

Abstract

Proxies for the composition of the ancient atmosphere are inaccurate and rarely quantitative. Estimates of pCO2 and pO2 in Earth’s deep past are particularly poorly constrained; in periods as recent as the Mesozoic, atmospheric pO2 estimates disagree by 50%. We address this conundrum by quantifying the contents of fluid inclusions in minerals formed in surficial environments that capture geochemical snapshots of the overlying atmosphere. We developed an analytical technique whereby inclusions are mechanically decrepitated and contents released directly into a quadrupole mass spectrometer. In addition, a gas-aqueous partition based on measured N2/Ar ratios provides a method for determining the atmospheric gas composition that equilibrated with aqueous fluid prior to entrapment. We examine three mineral systems from two case studies – the Mesoproterozoic ‘boring billion’ (~1.4 Ga), and the End Triassic Extinction (ETE) that is temporally associated with the eruption of the Central Atlantic Magmatic Province (CAMP, ca. 201.5 Ma). Lacustrine halite from the Sibley group (Ontario Canada) provides a snapshot of the Mesoproterozoic atmosphere from the 1.443 Ga Outan Island Formation, which we find was dominated by N2 and contained 23.8 ± 15.7 mbar O2, and 3.82 ± 1.41 mbar CO2. The high pO2 coincides with the diversification of plastid-bearing eukaryotes (red algae), and moderate CO2 density indicates Earth’s climate was warm enough to avoid global glaciation. In the Triassic we find coherence of atmospheric gas concentrations measured from inclusions in deep marine and palustrine cherts and paleosol carbonates. Remarkably, these determinations from three contemporaneous but geographically disparate depositional regimes converge on single values for atmospheric pCO2 and pO2. Moreover, both the marine and terrestrial realms show a contemporaneous increase in pCO2 coincident with the emplacement of the initial pulse of CAMP lavas and the ETE. In addition, argon isotope analyses of the Triassic cherts reveal significant radiogenic Ar, indicating that the entrapped gas is indeed ancient.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-405432

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