Ancient Oil and Mass Extinctions: Can We Connect the Dots?
Mass extinctions have played an important role in the evolution of Terrestrial life. With each mass extinction, the way is cleared for the spread and adaptation of surviving species, and for the emergence of new species. But that is not what we will talk about today.
Recent findings in geochemistry have called into doubt some of the pet theories of climate
Periods of oceanic anoxia have had a major influence on the evolutionary history of Earth and are often contemporaneous with mass extinction events. Changes in global (as opposed to local) redox conditions can be potentially evaluated using U system proxies. The intensity and timing of oceanic redox changes associated with the end-Permian extinction horizon (EH) were assessed from variations in 238U/235U (δ238U) and Th/U ratios in a carbonate section at Dawen in southern China. The EH is characterized by shifts toward lower δ238U values (from -0.37‰ to -0.65‰), indicative of an expansion of oceanic anoxia, and higher Th/U ratios (from 0.06 to 0.42), indicative of drawdown of U concentrations in seawater. Using a mass balance model, we estimate that this isotopic shift represents a sixfold increase in the flux of U to anoxic facies, implying a corresponding increase in the extent of oceanic anoxia. The intensification of oceanic anoxia coincided with, or slightly preceded, the EH and persisted for an interval of at least 40,000 to 50,000 y following the EH. These findings challenge previous hypotheses of an extended period of whole-ocean anoxia prior to the end-Permian extinction. _PNAS
More information on the study
The suggestion is that the ocean anoxia was secondary to the main extinction event, rather than being the cause. More study will be necessary to validate the isotopic techniques utilised. But this finding cannot but be a disappointment to the politically correct denizens of deep climate
But what interests Al Fin know-it-all-o-tologists about this information, is how it may relate to the topic of the production and sequestration of ancient oil. Deep ocean anoxia is not only related to mass extinction events, it is also a component of oil formation in the deep seabed.
Sea bottom anoxia occurs routinely at the mouths of large rivers, where massive sediment routinely buries dead sealife that is constantly deposited on the seafloor. That is why rich oil fields are often found offshore of large river deltas -- either where the deltas are now, or where they were hundreds of millions of years ago.
An ancient oil sleuth must be able to backward-trace the movements of continents and great river valleys, in order to know where to look for such sediment-buried deposits.
Another cause of mass sediment burial of seafloor organic material, is massive volcanic activity. This would be particularly important to an ancient oil sleuth when a group of volcanoes might stay active for millions of years, in the same general vicinity upwind of river deltas or rich upwelling currents.
But in cases of mass extinctions, the large scale deep ocean anoxia occurring at the same time as massive deposition of organic material onto the seafloor, might be a particularly rich time for the initiation of large scale oil production.
When this process occurs over continental crust, the oil can be preserved for a very long time. If it occurs over oceanic crust, the oil may be subducted with the crust into the mantle, where it will likely be converted into short chain hydrocarbons, CO2, CO, and other forms of carbon. The short chain hydrocarbons may return to the crust, and may eventually be recovered economically. Diamond and graphite may also return to depths which allows humans to recover them economically.
Regardless, it is the ancient oil we are interested in. The challenge is to connect the extinction events, the ocean anoxia, and the ancient geographic patterns together, to provide the best guess for the locations of giant oil deposits which might conceivably still exist in an undiscovered, but ultimately recoverable state.
Humans have become accustomed to utilising the easy oil, and are just now getting good at recovering oil from the harsh, deep ocean environments. That is a good thing, because the Earth is 70% ocean-covered.
Still, some the planet which was once covered by oceans is now dry land, and such places -- if they fit the criteria above -- might be some of the first locations to check out.
First published at Al Fin, the Next Level
Postings from Al Fin blog on "Oil from ancient seas"