The Los Angeles basin is a polyphase Neogene basin within the San Andreas transform system between the Pacific and North American plates. The basin was initiated in the mid-Miocene by widespread extension associated with significant strike slip and rotation of the Transverse Ranges of southern California. Late Miocene to early Pliocene extension, which accompanied the opening of the Gulf of California, led to the principal phase of basin opening. The early Pliocene to Recent deformational history of the basin is characterized by shortening associated with the active North Los Angeles fold and thrust system.
The Los Angeles basin is the richest basin in the world in terms of hydrocarbons per volume of sedimentary fill. Each phase of basin evolution has contributed to the basin's productivity. Some aspects of the basin's history that have affected the occurrence of oil and gas are related to basin-forming mechanisms and can be used to guide thinking in similar settings. Other first-order controls on hydrocarbon occurrence stem from processes that operated on a much larger scale and are not related to basin type. Deposition of thick, high-quality source rock within the Los Angeles basin is the result of such regional controls.
The polyphase history of the Los Angeles basin demonstrates the complexity that can occur along active transform margins. Such complexity can be expected in basins that have formed in similar settings.
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“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