Hydrocarbon Analysis of Hamersley Basin Deep Drill Cores: Preliminary Results

Characterization of the organic constituents of Precambrian rocks is complicated by serious questions as to the provenance of organic material recovered from such ancient and generally altered deposits. The problem is particularly acute in Archean terranes where the rocks are invariably metamorphosed to some degree. Organic matter indigenous to the original depositional environment of the host sediments can be difficult to distinguish from material that subsequently migrated into the rock from other sources. Further, contamination by ubiquitous petroleum products and derivatives can easily be introduced at any point during sample recovery and preparation. Nevertheless, analysis of the molecular and isotopic signatures of Archean biomarker compounds has the potential to provide key insight into ancient biology and ecology. Several continental drilling efforts in recent years have concentrated on obtaining organic-bearing sedimentary samples of low metamorphic grade from Archean and Paleoproterozoic terranes while minimizing sources of contamination. Experimental techniques have been developed to avoid laboratory contamination and to assess the origins of various types of organic matter. Using ultraclean protocols, and a combination of molecular, isotopic and geologic evidence, confident assessments can be made as to the syngeneity of biomarkers in Archean rocks. We present results of analyses of drill core collected from the Hamersley Basin, Western Australia in the summer of 2004.