Reference

According to abiogenic hypotheses, the main types of carbon compounds that may exist in the Earth's mantle include hydrocarbons, primarily methane, elemental carbon, carbon dioxide, and carbonates. Some sources also suggest the existence of iron carbide in the upper mantle. These compounds are believed to generate in the mantle and can migrate into the Earth's crust through deep faults, forming oil and gas deposits. Abiogenic theories propose that these compounds are formed from materials deep within the Earth, as opposed to biogenic processes which involve the transformation of organic matter. This perspective is an alternative to the widely accepted view that most hydrocarbons are produced from the remains of ancient organisms. For more detailed information, you can refer to sources like the Wikipedia page on Abiogenic petroleum origin.