Evidences for Pre-Jurassic oils in the North Sea

Embla field producing oil from Permian and Devonian reservoirs:

Reservoir sand with GC trace of produced oil:

Core plugs of Embla rhyolites with GC of biodegraded oil, and re-generated waxy oil from the biodegraded oil. The latter was trapped in fluid inclusions roughly 200Ma ago, ie. Pre-Jurassic:

Typical Kimmeridge oil with low wax, concave n-alkane profile, absence of gammacerane whereas Paleozoic sourced oils are different:

Pre-Jurassic oil from the North Sea characterized by even/odd predominance and high ETR:

Light oil fraction of some North Sea oils. Some show a pattern suggesting that they originate from a carbonate source:

Isotopically very light Paleozoic derived oils are clearly differentiated from isotopically heavier U. Jurassic derived oil and from the isotopically heaviest coal derived oils: