PAH refractory index as a source discriminant of hydrocarbon input from crude oil and coal in Prince William Sound, Alaska

Geochemical correlation and differentiation of hydrocarbons from crude oils and coals is difficult. The complex mixture of the hydrocarbon constituents and the dynamic nature of these constituents in the environment as they weather contribute to this difficulty. A new parameter, the polycyclic aromatic hydrocarbon (PAH) refractory index, is defined here to help in this correlation. The PAH refractory index is a ratio of two of the most refractory constituents of most crude oils, namely triaromatic steranes and monomethylchrysenes. These are among the most persistent compounds in oil after deposition in the environment and thus retain reliably the signature of the original petroleum input. This index is utilized in Prince William Sound (PWS) to differentiate three different oils, as well as to provide evidence that coal, not oil, is the dominant source of the PAHs which are prominent constituents of marine sediments from PWS and the Gulf of Alaska.