Sulfur and carbon isotope analyses of the 2.7Ga Jeerinah Formation, Fortescue Group, Australia.

Abstract

Sulfur and carbon isotope ratios have been determined on carbonaceous shales of the 2.7 Ga Jeerinah Formation, Hamersley Group, Australia. The analyses were performed using the Nd-YAG laser microprobe method.The δ 13 C (PDB) values of organic matter range from -38.3‰ to -35.1‰ with an average of -37.0‰ (44 analyses). These carbon isotope compositions support the previously proposed hypothesis that methanogens and methanotrophs were involved in the carbon cycles in the 2.7 Ga Hamersley ocean. Sulfur isotope compositions are ranging from +0.4‰ to +10.2‰ with an average of +4.6‰ (90 analyses). A notable feature is variable δ 34 S values within a micro-scale area; approximately 6 to 7‰ variations of δ 34 S values were detected within 5 × 5 mm areas. Such δ 34 S variations clearly indicate that pyrites in the Jeerinah shales were formed as a result of the sulfate reduction. This suggests that the 2.7 Ga Hamersley ocean contained appreciable amount of dissolved sulfate, opposing to the previously popular H 2 S-rich ocean model. Because of no evidence for the hydrothermal alterration on the examined samples, pyrites in the 2.7 Ga Jeerinah shales were most likely formed by the biological sulfate reduction in sediments.ganisms were active in the 2.7 Ga ocean and that these organisms played an important role in the global carbon cycle. These suggestions were based on the discovery of organic matter with extremely light δ 13 C values, -60 to -40‰, in some sedimentary rocks in the Hamersley Basin in Australia, in the Abitibi greenstone belt in Canada and the Transvaal basin in South Africa (Hayes et al

Carbon and sulfur isotopic signatures of ancient life and environment at the microbial scale: Neoarchean shales and carbonates

“…Previous δ 34 S measurements of Jeerinah Fm pyrite using laser ablation showed 6–7‰ mm‐scale heterogeneity, interpreted as strong evidence for microbial sulfate reduction (Kakegawa et al ., ; Kakegawa & Nanri, ). The sample of the Jeerinah Fm analyzed in this study exhibits even larger, micrometer‐scale heterogeneities in δ 34 S, Δ 33 S, and Δ 36 S (e.g., RHDH2a 285.3#16 and #19; Fig.…”

Evolutionary timing of the origins of mesophilic sulphate reduction and oxygenic photosynthesis: a phylogenomic dating approach

“…(2001) reported sulphides in 2.7 Ga shales to have δ 34 S values as low as −19.9 and an ɛ max of 36.6. Archean carbonaceous shales, by contrast, show very little sulphur isotopic fractionation (Watanabe et al ., 1997; Kakegawa et al ., 2000; Ono et al ., 2003). Large fractionations of sulphur isotopes that are unambiguously due to large‐scale bacterial sulphate reduction are not observed until about 2.35 Ga (Cameron, 1982; Hattori et al ., 1983, 1985), or just before or nearly concurrent with the inferred oxygenation of the atmosphere.…”

Diamond growth from oxidized carbon sources beneath the Northern Slave Craton, Canada: A δ13C–N study of eclogite-hosted diamonds from the Jericho kimberlite

“…However, there are also examples in the Archean to Proterozoic sedimentary record where 13 C-depleted organic matter is hosted within thick black shales with little carbonate content. For example, the carbonate-poor Neoarchean shales of the Jeerinah Formation of the Hamersley Basin contain abundant organic matter (TOC 2-4 wt.%) with d 13 C values from À35& to À39& and (Kakegawa et al, 2000). Similarly, in the ca.…”

“…This anomaly is found, for example, in rocks of the ca. 2.0 Ga Zaonezhskaya Formation located on the Kola Peninsula, NW Russia (Melezhik et al, 1999), the 2.7 Ga Abitibi and Wabigoon Belts of the Superior craton, Canada (Strauss, 1986), and from Late Archean sediments of the Hamersley Basin in Australia (Kakegawa et al, 2000;Eigenbrode and Freeman, 2006;Thomazo et al, 2009). These extreme carbon isotope compositions are thought to be the product of methane-fixation by methanogenic bacteria (Eigenbrode and Freeman, 2006).…”