Actually Petroleum ITSELF, not the rocks around it, contains chemical indications of the diatoms, bacteria, etc. it formed from...
For example:
http://www.stw.nl/projecten/B/bar/bar5275.htm
"Chemical fossils are characteristic compounds found in oils that are derived from specific algae and bacteria, which were abundant during the deposition of the source rock of the oil. Since these organisms, and therefore their characteristic compounds, were only evolving during specific periods in Earth's history, they are used to constrain the age of petroleums. This is of significant benefit for solving exploration and production problems of oil companies, especially when source rocks of oils are not known for instance with deeper buried source rocks. However, the number of useful age-related chemical fossils is still limited, especially in the age-range 0-180 my. Chemical fossils of diatoms may provide useful age-diagnostic compounds since they evolved during that time period but unfortunately little is known about the composition and evolutionary origing of diatom lipids. Therefore, we porpose to grow a wide diversity of extant diatom species and etermine their lipid composition as well as their 18S ribosomal RNA (rRNA) sequences. These sequences will be used to establish relationships between different diatom species."
And again one has to get by the basic problem that the majority of the people eagerly buying into the "oil is not a fossil fuel" theories all seem to believe that stupid mainstream geologists think oil comes from the dead bodies of Brontosauruses...
And also,I suspect, don't even know or understand what plankton or a diatom is.
I'm far from buying this theory unless someone manages to prove it.
But I don't see why diatoms couldn't get into oil via movements of the earth. After all, if you can have ancient shells up in the Himalayas because of the movement of the Indian subcontinental plate, and all sorts of various rocks and other objects squeezed into conglomerate rock, why not diatoms in oil?
By the same token, it's possible to imagine how oil can get down pretty deep, so proving this theorem would require more than just finding a few deep reserves.