Carbon dating crude oil
NEWS RELEASE 08/04/94 CONTACT: Stanford University News Service (650) 723-2558 STANFORD -- The Jurassic (180 million to 140 million years ago) was a very good age for oil formation.So too was the Cretaceous (140 million to 65 million years ago).It is called "Carbon-12," which is abbreviated "C." The fact that the atom has six protons is what makes it carbon.Most nitrogen atoms have seven protons and seven neutrons, so their atomic mass is 7 7 = 14.Because the geological processes involved convert the oleanoids in the angiosperms into oleanane, the more oleanane found in a given oil sample, the more recent it is likely to be. Oils of any age can lack oleanane if flowering plants were not part of the material from which it formed.But lack of oleanane is a significant clue that the oil may have formed in the Jurassic or older times, before angiosperms evolved.
Because angiosperms become more plentiful as time progresses, younger organic deposits that are converted into oil are likely to contain more angiosperms.
Because hopane should degrade at about the same rate as oleanane, the ratio of the two should be relatively independent of the petroleum's thermal history, the researchers said.
When they obtained these ratios and compared them with the age of their samples and the number of families of angiosperms in the fossil record, they found that, although there were some differences, variations in the level of the biological marker are broadly consistent with the fossil record.
Therefore, dating can help petroleum geologists determine the specific "plays" - geological environments - on which they should concentrate their efforts, Moldowan said.
To calibrate this scale, the scientists first measured the amount of oleanane in 103 samples of petroleum source rock that could be dated by conventional means.