FACIES AND BIOLOGICAL CONTROLS ON THE PRESERVATION OF ATMOSPHERIC INPUTS IN ARCHEAN MARINE ENVIRONMENTS

The modes of sulfur preservation as pyrite in a variety of marine facies are important to understand the sources and sinks of atmospheric and terrestrial inputs to the Archean marine environments. To evaluate these issues we studied the recently-drilled AIDP-2 core, which intersects the Jeerinah and overlying Carawine formations (~2.65-2.55 Ga) from the Hamersley Province in Western Australia. Our time-series isotopic study demonstrated that pyrites in the deep water organic-rich shale and limestone facies of the Jeerinah Formation preserved progressively positive Δ³³S and δ³⁴S signatures that lie along the previously established Archean Reference Array [1, 2]. In marked contrast, the shallow marine dolomites of the Carawine Formation are characterized by moderate positive to negative Δ³³S signals with variable and some strongly negative δ³⁴S values, especially preserved in macroscopic pyrite that was micro-drilled from dolomite samples. These observations suggest that the primary sulfur source for Carawine pyrite was sulfate from atmospheric and/or terrestrial sources with negative or near 0‰ Δ³³S isotopic compositions that was reduced through microbial sulfate reduction. On the other hand, sulfur in shale and limestone facies appears to have mostly originated from an atmospheric source of elemental sulfur with positive Δ³³S signatures. Neoarchean oceanic sulfate, which is estimated to have been ~1000x less than in Modern seawater [3, 4], may have been concentrated in shallow environments and utilized by sulfate reducers. In contrast, particulate elemental sulfur appears to have preferentially accumulated in deeper environments where it was converted to sulfide through biological sulfur reduction/oxidation processes. [1] Ono et al. (2003). EPSL, 213(1), 15-30. [2] Kaufman et al. (2007). Science, 317(5846), 1900-1903. [3] Crowe et al. (2014). Science, 346(6210), 735-739. [4] Zhelezinskaia et al. (2014). Science, 346(6210), 742-744.