Source rock potential of Franciscan complex: the galloping gourmet and the hydrocarbon kitchen

Previous workers suggested that western North America was characterized by coastal upwelling during much of the Mesozoic and Cenozoic Eras. Areas of coastal upwelling are commonly characterized by excellent source rocks - because high-quality organic matter is preserved in oxygen-minimum zones - and by high sedimentation rates. The Franciscan complex, of Jurassic to Miocene age, records part of the interaction between Pacific oceanic plates and the North American continental margin. The Franciscan complex is an amalgam of terranes, most of which represent deposition in deep to intermediate-depth waters on oceanic lithosphere and trench-related continental margin facies. The authors analyzed the source rock potential of Franciscan complex rocks using Rock-Eval pyrolysis techniques. Turbiditic mudstones of the eastern belt Franciscan complex contain moderate amounts of total organic carbon (TOC about 1%), but have low volatile contents as indicated by hydrogen and oxygen indexes. TOC is 1-3% for organic matter in argillaceous melange matrix of the coastal belt of northern California, the Permanente terrane, and San Simeon; however, volatile content is low. The Calera limestone of the Permanente terrane was deposited under locally anoxic conditions, probably on a mid-Pacific seamount, and later accreted to North America. It contains from 0 to 7% TOC,more » and volatile content is low. Significant volatile content is found only in turbiditic mudstones of the coastal belt Franciscan, northern California, where TOC averages about 1% in Type III kerogens. Slates locally bearing blue amphiboles, lawsonite, jadeite, and limestones tectonically interleaved with slates in melange on Cedros Island, Baja California, contain up to several percent TOC, but are extremely depleted in volatiles.« less