Unusual geo-dating technique

New isotopic measurements could show that some estimates of oil generation timing may be off by tens of millions of years. The technique of using rheniumosmium as a radiogenic clock has only been possible within the last decade, But nowadays we can detect isotopes in the parts-per-trillion range. The technique has the potential to date many oil reservoirs worldwide, and could help identify the ages of source rocks from which known oil deposits originated.

Rhenium occurs at about 200 parts per trillion outside the Earth's core. It comes in isotopic weights of 185 and 187. Rhenium-187 is very slightly radioactive, turning into osmium-187, with a half-life of 42.3 billion years. Thus, osmium very slowly collects more of the 187 isotope. It is a dreadfully slow and extremely rare radioactive clock. But we now have the technology to reliably measure this isotopic ratio.

The ratio can be affected, that is, reset, by various high-temperature processes acting on its parent rock. There is some noise introduced in ratios that are this small, and geo-dating may be impossible if the source rock is unknown.

Geologists David Selby and Robert Creaser from the University of Alberta, recently used the ratio to date the oil in Alberta's oil sand deposits. They tested the black shale source rock, and then the oil, and compared the isotopic ratios in the two samples. The result was 112 [+ or -] 5.3 mya oil, which is 60 million years earlier than previously thought. What was important was the accuracy of the finding. It tries to pinpoint the time of oil genesis.

For petroleum exploration, knowing the age of hydrocarbons places constraints on where they might accumulate. In my view, the utility and accuracy of the new technique still needs some further validation before its utility is fully understood. But, it offers a new potential tool in certain circumstances.