Significant accumulations of hydrocarbons may be present within Miocene and younger strata that fill several deep-water basins in the outer southern California borderland. Multichannel seismic reflection and sonobuoy refraction profiles across one of these basins (informally termed Patton basin) reveal a moderately thick sedimentary section overlying acoustic basement. Patton basin lies between the northern segments of the Patton and Santa Rosa-Cortes Ridges and has an average seafloor depth of about 1,200 m. The sedimentary section within Patton basin ranges from 1.6 to 3.5 km in thickness, with the thickest part (2 to 3.5 km) located at the northern end of the basin. Tanner basin, which joins Patton basin at the south, probably contains a greater thickness of sediment.

Strata that crop out on the adjacent ridges can be traced beneath Patton basin on acoustic-reflection profiles. Based on samples from these ridges, acoustic basement within the basin consists of rocks that are assigned to the Franciscan assemblage. Acoustic basement is overlain unconformably by about 1,500 m of lower and middle Miocene strata. These strata are faulted and folded and are in turn unconformably overlain by as much as 2,000 m of less deformed late middle Miocene and younger strata. Overall, the basin appears to have stratigraphic and structural characteristics that are similar to the hydrocarbon-producing parts of the onshore Santa Maria basin.

Several characteristics of the Patton basin sediment make this basin and adjacent outer borderland basins favorable targets for hydrocarbon exploration: (1) Organic geochemical analysis of bottom samples from outcrops and well data indicate that the lower and middle Miocene strata filling the lower half of the basin are good to excellent potential source rocks. (2) Based on seismic reflection profiles and a nearby DSDP Site, sandstone of good reservoir quality may unconformably overlie the older strata. (3) Data from DSDP Site 467 suggest that strata within the borderland basins have been subjected to higher temperatures than time-equivalent, marginally mature strata that crop out on adjacent ridges. (4) Numerous structural and stratigraphic traps are present.

End_of_Article - Last_Page 440------------