This process occurs over a very large time scale, and acts as one of the major mechanisms for fossiliferous organic carbon to be released back into the environment.
For decades, it was thought that the majority of the organic-rich sedimentary beds deposited on the ocean floor was a byproduct of three environmental variables: the input of organic material, the rate of sedimentation, and the amount of deep-water oxygenation.
For example: In case studies of the Black Sea, a modern anoxic environment, it has been shown that anoxia within the lower-levels of the water column alone do not produce significant amount of organic-rich sediments, even though sufficient organic material was supplied to the region in the Holocene.
Therefore, the new theory is that "primary producers" higher in the water column are responsible for the majority of the deposition of carbon-rich sediment in continental margin environments.
[2] Based upon a study conducted involving ocean-circulation models in the Cretaceous, it was found that although conditions were relatively similar to those today, the oceans had much harsher currents that influenced the water column.
[citation needed] Studies of many and varied sedimentary sites are required to come to such conclusions; there are myriad bacterial species, and each organic source rock may have differing interactions with these bacteria.
The combination of microscopic and molecular studies should be addressed when interpreting abundances of bacterial biomarkers present in a petroleum source and its influence on the total organic carbon.