The transfer of organic signatures from bedrock to sediment

A case study in the Canadian Arctic demonstrates how an organic geochemical signature in the regional bedrock can be transferred by erosion and redeposition to younger geological formations and surface sediments. The hydrocarbon composition recorded in Laurentian (Lower Palaeozoic) carbonate bedrock was incorporated into overlying Miocene and Quaternary formations, and modern mass waste, alluvium, snow/ice, and proglacial deposits, and further distant in ice-rafted detritus. The retention of the original geological organic signature is reflected in consistent thermal maturities (hopane ratios) and environmental indicators (sterane distributions). In the modern sediments, the geological signature is variably mixed with a modern microbial organic signature reflected in high values of carbon preference index and diploptene. These data show that hydrocarbon occurrences in bedrock may be detected by the analysis of surface detritus, especially in carbonate terrains. However they also indicate that environmental signatures may be misleading if they are inherited from older geological units. (C) 2007 Elsevier B.V. All rights reserved.