The Los Angeles basin is a small but relatively deep Neogene basin located in the most northeast portion of the southern California continental borderland. It was formed along a transform margin during the early to middle Miocene, as were numerous basins within the continental borderland south of the Transverse Ranges.

A series of prograding submarine fans filled most of the basin during the middle to upper Miocene, Pliocene, and Pleistocene. The morphology of these fans appears to fit most basin-floor fan models but these models were greatly modified by paleobathymetry. The sediment transport mechanism was primarily turbidity flows from submarine canyons but other mass sediment transport such as debris flows, fluidized sediment flow, grain flow, etc was also significant.

Three primary, often coalescing, submarine fans have been recognized: the Tarzana fan in the northwestern Los Angeles basin, the San Gabriel fan in the central and southern parts, and the Santa Ana fan in the eastern part of the basin. Most of the oil produced in the Los Angeles basin comes from submarine fan sandstones. Much of the future oil to be found will be from the same fans or heretofore unrecognized submarine fans. Structural geologic concepts will be of equal importance when exploring for these subtle traps.

Total cumulative production to 1982 has been 7.3 billion bbl of oil and 5.8 tcf of gas. Per unit volume of sediment, the Los Angeles basin is one of the richest in the world. It was a silled basin within the oxygen-minimum oceanographic zone during the upper Miocene and Pliocene. A combination of rich biogenic sedimentation along with rapid burial by coarse to fine clastics and relatively high paleoheat flow provided almost perfect conditions for the generation and migration of oil and gas. Structural deformation was intermittent throughout the Neogene but was most intense and culminated in the late Pleistocene to Recent. The multistoried oil sands with different crude oil types suggest most of the oil is indigenous to the formation in which it is found.

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