Which kerogen type is typically associated with rocks deposited in marginal marine environments and is a major oil source?

• A. Type II Kerogen
• B. Type I Kerogen
• C. Type III Kerogen
• D. Type IV Kerogen

Answer: (A)

Think in terms of where the organic matter comes from and what it yields when heated. In rocks formed at the edge of the sea, the preserved organic material is primarily marine in origin—plankton and algae. This marine, oil-prone mix becomes Type II kerogen, which is well suited to generating liquids (oil) under the right burial temperatures. That’s why these rocks often become major oil source rocks. Other kerogen types come from different environments: Type I from freshwater lake sources is also oil-prone but not typically associated with marginal marine deposits; Type III from land plants tends to produce gas; Type IV is largely inert carbon with little hydrocarbon potential. So marginal marine deposits hosting marine organic matter point to Type II kerogen as the primary oil source.