BIOMARKER BINDING INTO KEROGENS - EVIDENCE FROM HYDROUS PYROLYSIS USING HEAVY-WATER (D2O)

Solvent-extracted Kimmeridge Clay Formation kerogen was heated to 315 degrees C for 72 h in the presence of excess water (H2O) or heavy wate r (D2O). Hydrocarbons generated from the kerogen during the D2O experi ments contained variable amounts of deuterium atoms [0 to as high as 1 2 deuterium atoms per molecule in the compounds we examined (mean of < 0.5-4.2 atoms), varying with compound type and pyrolysis conditions]. The observed patterns of deuteration are nor a function of simple homo geneous exchange, but must derive from the cleavage process in the pre sence of excess D2O. The diagnostic mass spectral fragment ions (elect ron impact ionisation) of selected regular acyclic isoprenoid alkanes, hopanes and steranes generated in the presence of D2O showed highly l ocalised areas of deuteration, at or near the positions or functionali ty in the original biological precursor molecules. We interpret deuter ation to have occurred at, or in close proximity to, the inferred link ages (e.g. ether or sulphur) by which the different biomarker hydrocar bons were formerly attached to kerogen (i.e. the tail of the asymmetri c acyclic isoprenoids, the A-ring of steriods, and the side chain of h opanoids). (C) 1998 Elsevier Science Ltd. All rights reserved.