Exobiology and Evolutionary Biology

Sulfur triple isotope stratigraphy of Archean Drill Core material

PI: James Farquhar

This project will focus on collecting and interpreting the multiple-sulfur data for the NASA Astrobiology Drilling Program (ADP) Hammersley-Fortescue core. A funded NSF investigation involving the collaborators of this proposal (but not the PI) supports collection of general lithological characterization, cm-scale logging, thin section microscopy, micropaleontology, and sedimentary petrology of all rock types as well as biomarker analysis, inorganic redox proxies, elemental and isotopic characterization (but not multiple-sulfur isotopes) of all major lithologies. The funds requested here will support efforts by the PI to join with these efforts by bringing a new tool and expertise to bear on this research. Multiple-sulfur isotope analyses will be undertaken using two analytical techniques available at the University of Maryland – a new rapid technique for obtaining Δ ³³ S and Ó ³⁴ S using EA combustion followed by continuous-flow IRMS of SO, and an established technique for obtaining high precision and accuracy determinations of Δ ³³ S and ?36S using fluorination and gas chromatography followed by dual inlet IRMS of SF6. The rapid determination of Δ ³³ S and δ ³⁴ S by EA-IRMS of SO provides an opportunity to survey the multiple-sulfur isotope record in the Hammersley- Fortescue ADP core at a meter scale allowing us to select targets for the high precision Δ ³³ S and Δ ³⁶ S by dual inlet IRMS analysis of SF ₆. The goals of this project include:

(1)establishing a record of Δ ³³ S and δ ³⁴ S for the Hammersley-Fortescue ADP core that can be used to evaluate systematic variations of Δ ³³ S and δ ³⁴ S between this and other cores (e.g., ongoing work by S. Ono at the Geophysical Laboratory for Agouron- Griqualand Paleoproterozoic Drilling Project (AGPDP) drill cores from the Transvaal supergroup),

(2)establishing the relationship between Δ ³³ S and D ³⁶ S (Δ ³⁶ S / Δ ³³ S) for different parts of Hammersley-Fortescue ADP core (Work undertaken at UMCP and the Geophysical Laboratory over the past year and a half has led to the observation that Δ ³⁶ S / Δ ³³ S varies for different formations, and can vary as a function of the stratigraphic position of samples within a single formation. It has not been established whether these variations are consistent for the same stratigraphic levels in different cores.), and

(3)evaluating the significance of the Δ ³³ S, Δ ³⁶ S, and δ ³⁴ S record that we observe in the Hammersley-Fortescue ADP core in the context of the lithological, geochemical, and isotopic characterization of the core material that being undertaken by the collaborators to this proposal.

The combination of high throughput and high precision analytical capabilities for measuring δ ³⁴ S, Δ ³³ S and Δ ³⁶ S at the University of Maryland and the expertise of the PI (Farquhar) and of the collaborators for collecting and interpreting data for the Hammersley-Fortescue ADP core presents a unique opportunity to study the evolution and cycling of sulfur during the middle and late Archean.