Structural Geology and Tectonic Evolution of Los Angeles Basin

Thomas L. Wright

Oil in the Los Angeles basin has accumulated principally in anticlinal folds associated with strong Neogene faulting and compression. The still-continuing Pasadenan orogeny, involving northwest-trending right-lateral wrench faults related to the San Andreas system, has been the dominant influence. But that deformation has been overprinted on structures formed during two discrete earlier orogenic episodes: (1) the major widespread block faulting of the middle Miocene and (2) a less-obvious phase of compressive deformation that occurred during latest Miocene and earliest Pliocene time, involved left-lateral faulting--and related folding--on more westerly trends, and was especially significant along the northern margin of the basin. The resulting present-day structural patte n, therefore, is not a simple pattern of classical right-lateral wrench-fault deformation. It is a pattern which reflects the radical Neogene evolution of the regional stress field, and the interplay of wrench faulting with the hinge lines and strong sedimentary wedge belts formed by earlier vertical movements.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.