Early 20th century; earliest use found in American Journal of Science. From petro- + -genic, after petrogeny.
petrogenic2
/ˌpɛtrə(ʊ)ˈdʒɛnɪk/
adjective
Relating to or denoting hydrocarbons (such as those in petroleum), formed by the decomposition of organic matter by processes occurring in sediments at elevated temperatures and pressures.