Organic geochemistry of impactites from the Haughton impact structure, Devon Island, Nunavut, Canada

Organic matter in impactites from the 24 km wide and 39 Ma old Haughton impact structure, Canadian High Arctic, is a mixture of fossil and modern biological components. The fossil component represents a conventional oil that was generated from Lower Palaeozoic marine source material before impact and permeates bedrock dolomites. Biomarker maturity parameters record the thermal effect of the mid-Tertiary impact. Maturity-influenced sterane, rearranged hopanoid, and triaromatic steroid ratios all increase towards the centre of the impact structure, where thermal alteration was greatest. The heating was probably dominated by an impact-related hydrothermal system, as such systems last long enough for kinetically-based thermal alteration to occur. Kinetically-related biomarker data suggest that the hydrothermal heating lasted for c. 5000 years. Biomarkers are also preserved in dolomite clasts within impact melt breccia, and indicate strong thermal alteration. Modern biological contamination of the rocks is responsible for the superposition of two geochemical signatures (which could be cyanobacteria, non-marine algae, or higher plant matter) onto the fossil component, but they can be recognized and distinguished. The data show that the impact structure system holds a record of both the pre-impact organic signature and the thermal signature of the impact, and thereby indicates that organic geochemistry is a valuable tool in documenting the response of rocks to impacts.