The Los Angeles basin is a small, deep Neogene basin located in the northeast portion of the southern California continental borderland. It was formed along a transform margin during early to middle Miocene time, as were numerous basins within the continental borderland south of the Transverse Ranges.
A series of submarine fans were deposited in the Los Angeles basin during the middle to late Miocene, Pliocene, and Pleistocene.
The configuration of these fans appears to fit several basin-floor fan models, but the fan morphologies were greatly influenced by local paleobathymetry. The primary sediment transport mecha- nism was turbidity flows from submarine canyons, but other mass sediment transport mechanisms, such as debris flows, fluidized sediment flows, and grain flows, were also significant.
Three primary, commonly coalescing, submarine fans have been recognized: the Tarzana fan in the northwestern Los Angeles basin, the San Gabriel fan in the north central portion, and the Santa Ana fan in the eastem portion of the basin. Most of the oil produced in the Los Angeles basin comes from upper Mohnian, Delmontian, and Repettian sandstone and conglomerate reservoirs of these submarine fans.
The Los Angeles basin was a probable silled basin that intersected the oxygen-minimum oceanographic zone during the late Miocene and Pliocene. A combination of the rich biogenic sedimentation along with rapid burial by coarse- to fine-grained clastics and moderate paleo-heat flow provided almost perfect conditions for the generation and migration of oil and gas. Stmctural deformation was intermittent throughout the Neogene but reached a culmination in the late Pleistocene to Recent.
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Active Margin Basins
“The most distinctive characteristic of the Los Angeles basin“The most distinctive characteristic of the Los Angeles basin is its structural relief and complexity in relation to its age and size” (Yerkes et aI., 1965, p. AI6); however, its very complexity caused no small amount of discussion in designing and naming this volume of the AAPG World Petroleum Basin Memoirs. (See the Foreword for a discussion of the scope of these memoirs.) The series coordinators decided early that the Los Angeles basin should be included in the World Petroleum Basins project because of its interesting geology and importance as a hydrocarbon producer. Initially, the Los Angeles basin was considered for a convergent-margin volume, presumably in recognition of the late-stage shortening that has taken place in the Los Angeles region of southern California. There is little doubt, however, that the Los Angeles basin has formed and deformed within the evolving San Andreas transform system (Atwater, 1970, 1989; Campbell and Yerkes, 1976; Blake et al., 1978; Engebretson et al., 1985; Wright, this volume). There is also little doubt among those who have worked in the area that the initial subsidence of the Neogene Los Angeles basin was caused by extension (Yeats, 1968; Crowell, 1974, 1976, 1987; Wright, this volume). The series coordinators decided, therefore, that to portray the Los Angeles basin as a model for basins formed in convergent-margin settings would be misleading.
The title of this volume, Active Margin Basins, is a compromise, but, like many compromises, this title falls short of completely describing its subject