@farmerman,
I just looked in my source rock data and the source marine rocks that serve as the petroleum source , are Oligocene lacustrine deposits of SHALES and SANDSTONES. (We must be really careful about conclusion jumping and Im really surprised at CW Hunt jumping to same)
There are three components to an oil deposit
1Source rock,-here the petroleum is actually formed via biogenic processes on biological detritus. In this case, the Oligocene
2Migration rock. -fractures allow for grvity collection and migration of the product to
3Storge unit-In the Bch Ho field, SOME of the storage is an igneou rock in which a full graben structure iwithin a granitic rock unit has acted as a thermos bottle for storage of the gravity separated ptroleum .
Its an abiogenic storage area, The oil itself is biogenic because the forams , flora and pollen, and other critters like diatoms clearly show the sources material were the lake deposits that covered half the area of SOuth Vietnam.
Thats a 25 cent explanation , Im sure omone can look up some scholarly work by SEPM or USGS about the Bach Ho field and its claim at abiogenic oil being a misnomer.
PS , gunga, being a "noted" geologist doesnt mean you are always right.