Abstract

Marfa Basin is a small foreland basin in southwest Texas which initially formed during the Ouachita Orogeny in late Pennsylvanian through Permian time. It has undergone two episodes of subsidence, and two phases of oil maturation. The initial episode of subsidence buried the southern portion of the basin and placed Woodford source rock into the oil window in Leondardian time. Hydrocarbons matured and migrated updip into various pre-Woodford structures. However, prior to the second period of subsidence, the entire region was exposed, which resulted in invasion of the Marfa Basin by meteoric waters. Fresh water recoveries from DST’s in the Ordovician through Permian sections help document meteoric invasion. Thus, any early formed structural traps may have been flushed during regional exposure in the Triassic or Jurassic.

The second eisode of subsidence occurred after the Mesozoic flushing event. During the Tertiary, Basin and Range faulting extended into Marfa Basin, resulting in down-drop of the northern part of the basin and deposition of over 3000 feet of volcanics. This younger burial event placed immature Woodford source rock into the oil window in late Eocene to Oligocene time. It is possible that a second period of oil generation and migration may have recharged updip traps. Recent seismic data shows several anomalies that could be interpreted as Guadalupian build-ups; however, these seismic anomalies could also be volcanic intrusions.