Preservation of Biological Signature within Impact Melt Breccias, Haughton

Introduction: The response of organic matter to impact events is of widespread interest for what it tells us about the likelihood of survival of life and/or fossilized biological signatures [1,2,3] following impacts. This is relevant to the history of life on Earth, and to our exploration of other solar system bodies, including Mars. The Tertiary Haughton Impact Structure, Cana-dian High Arctic [4], is well suited to such studies because the target bedrock consists of Lower Palaeo-zoic carbonates that contain kerogen and pre-impact hydrocarbon residues. A further advantage of using the Haughton Impact Structure is that there has been no heating in the crater after the impact event and subsequent hydrothermal activity. This enables us to compare the impact-affected rocks with rocks from outside the crater. Objectives: Previous research showed that although the crater centre registered greater heating than the rest of the crater, it still contains organic compounds that are a signature of fossil biological activity [3]. In the next phase of this research we have examined the Haughton carbonate impact melt breccia. This is a crater-fill deposit which is composed of lithic (non-melted) fragments of the target rocks, including clasts of the carbonate bedrock, embedded in a matrix of a carbonate/silicate melt. The melt experienced temperatures of at least 600 ºC [5] and possibly much higher. Our objective is to determine if biomarkers survived within the carbonate clasts embedded in the hot melt, and if so, to compare heating at the edge and the centre of the clasts, were the centre may have been buffered from extreme heat. Sampling and analytical procedure: The car-bonate clasts in the melt breccia vary in size from less than a centimetre to a few meters across. For investigation of a possible increase in heating from the centre of a clast to the edge of a clast, samples of clasts each of ca 20 cm 3 were sampled. Smaller sizes of clasts were also selected to see if there is a minimum size in which organic molecules are preserved. The matrix attached to the edge of the clasts was removed and the samples were cleaned with solvent to eliminate possible contamination. Material 0-1 cm from the edge and material from the centre of the