nai

Project Progress

Most fieldwork was directed towards drilling 3 deep diamond-drill cores in Australia for the NAI Astrobiology Drilling Program. These were completed through

1. the unconformity between the Coonterunah (3.52Ga) and Warrawoona (3.45Ga) Groups: 350 metres;
2. the lower Hamersley Group (2.65-2.47Ga): 1000 metres;
3. the Tumbiana Formation of the Fortescue Group (2.72Ga): 250 metres.

Notable intersections were: 1) a thickened basal sandstone unit to the Strelley Pool Chert in the Warrawoona Group; 2) two meteorite impact spherule horizons in the Wittenoom Formation; 3) ooid grainstones and evaporitic horizons in the Tumbiana Formation (Buick et al., 2004). Uncontaminated samples for organic geochemical investigation were collected immediately upon surfacing, which yielded confirmation that indigenous biomarkers compatible with host-rock thermal maturity are indeed preserved (Waldbauer et al., 2004).

Other fieldwork was conducted in the 3.52Ga Coonterunah Group, collecting samples for carbon isotope studies of metamorphosed early Archean sediments for comparison with older and more metamorphosed rocks from Greenland (Harnmeijer & Buick, 2005).

Studies completed during the year included:

1. a review of the Archean sulfur cycle and its constraints upon sulfur isotopic fractionation, confirming the existence of microbial sulfate reduction in ~3.5Ga oceans and showing that peripherally-branching bacterial phyla had already evolved (Shen & Buick, 2004);
2. a detailed geochronological transect through the ~2.7Ga Fortescue Group coupled to a paleomagnetic profile, which showed that apparent polar wander rates were periodically enhanced ten-fold over current maximum values. This implies that sea-floor spreading rates were much faster early in Earth’s history and, when contrasted with the intervening intervals of little apparent polar wander, suggests that tectonic plates were also smaller than at present.

Studies continuing included:

1. organic geochemistry of Paleoproterozoic oil-bearing fluid inclusions, to confirm the syngenetic origin of biomarkers;
2. organic geochemistry of mid-Archean shales, to extend the temporal biomarker record.