Source rock characterization and petroleum systems of Eocene Tyee basin, southern Oregon Coast Range, USA

The hydrocarbon source rock potential of the Eocene units in the southern Oregon Coast Range was evaluated using Rock-Eval pyrolysis. Most Eocene units in southern Oregon Coast Range are thermally immature and contain lean, gas prone Type III kerogen. However, some beds (coals) are sufficiently organic rich to be sources of biogenic and thermogenic methane discovered in numerous seeps. The overall hydrocarbon source rock potential of the southern Oregon Coast Range is moderately low; however, requirements for commercial accumulations of hydrocarbon probably exist locally within and adjacent areas. Two speculative petroleum systems are proposed. The first includes the southern part of the Oregon Coast Range near the border with the Mesozoic Klamath Mountains and is related to a proposed subduction zone maturation mechanism along thrust faults. The second occurs near the eastern border of the range where maturation is related to heating by sills and migration of hydrothermal fluids associated with mid-Tertiary volcanism in the western cascade arc.