Andrew Lim, of Dunedin, asks :-
Why has the abiogenic theory of oil formation failed to gain acceptance in general scientific concensus?
Richard Sykes, a rock and petroleum geochemist at GNS Science, responded.
The answer is because it can be demonstrated that virtually all commercial oil accumulations have a biological origin. They are derived in the main from marine or lacustrine (lake) phytoplankton or algae, or less commonly, from terrestrial plants. This can be shown from the presence of biomarker compounds within the oils. These compounds, which include steranes and hopanes, can be linked back to specific biological precursors.
I am most familiar with oils and gas condensates in Taranaki Basin where most of the oils and gas condensates are derived from coals and coaly mudstones. That is, they are derived from plant remains that accumulated in peat swamps, later to become coals and coaly mudstones. Many of these oils and gas condensates are rich in a compound called isopimarane, which is derived from gymnospermous plants, whereas other oils and condensates are rich in a compound called oleanane, which has been linked to angiosperm plants. Angiosperms didn't arrive in New Zealand in great abundance until the Tertiary period. Thus, we can use the relative abundances of angiosperm and gymnosperm biomarker compounds in the oils and gas condensates to say, for example, these oils are derived from Cretaceous coal measures sequences (as with the Maui, Maari and Tui oils), whereas other oils are derived from Tertiary coal measures (e.g. the McKee and Waihapa oils).
I have undertaken laboratory pyrolysis experiments to simulate the formation of oil and gas from different types of New Zealand coals and I've also looked at these coals under the microscope to observe the different types of plant components present. What I have shown is that it is the amount of preserved leaf cuticle material in the coals that primarily controls how much oil a particular coal can generate. Leaf cuticle is very waxy and this is why our oils also tend to be rich in wax (many are solid at room temperature). Coals rich in cuticle biomass are thus said to be "oil-prone", whereas those containing little or no cuticle, would produce only gas, perhaps with some condensate.