85. Ingersoll, R.V., D. S. Diamond, and P. Bird [2024]

Cretaceous through Neogene tectonostratigraphic evolution of the southern California margin, USA,

in Van Buer, N.J., and Schwartz, J.J., eds., Field Guides for GSA Connects 2024, Anaheim, California:

Geological Society of America Field Guide 70, p. 159–177, https://doi.org/10.1130/2024.0070(07).

Abstract. The paleotectonic evolution of the continental margin of southern California (USA) is recorded in the tectonostratigraphic record, much of which is exposed in the Santa Monica Mountains and their surroundings. This field trip examines the stratigraphic record that documents the Late Cretaceous through Neogene evolution of the southern California continental margin. The oldest exposed tectonostratigraphic units of latest Jurassic and earliest Cretaceous age (ca. 150–140 Ma) reflect poorly understood plate interactions, possibly coeval with or somewhat younger than the Nevadan orogeny recorded in the western Sierra Nevada, where an arc-arc collision likely occurred. These plate interactions preceded subduction of the oceanic Farallon plate, which initiated the Cretaceous–Paleogene arc-trench system (ca. 140–30 Ma), within which forearc strata accumulated. Cretaceous and Paleogene forearc strata represent times of both normal (ca. 140–80 Ma) and low-angle (ca. 80–40 Ma) subduction (Laramide). During the latest Paleogene, the arc-trench system was disrupted by interaction with the East Pacific Rise and related transforms, which resulted in progressive evolution of the margin from an arc-trench system into a transform plate boundary (ca. 30–0 Ma). Microplate capture, transrotation, transtension, and transpression have each left a stratigraphic record of these complex and superposed Neogene events. Depositional paleoenvironments included submarine fans, slopes, shelves, fluvial systems, alluvial aprons, and fan deltas. Key outcrops in the Santa Monica Mountains area illustrate these field relationships and paleoenvironments.  The overall purpose of this field trip is to observe key aspects of the stratigraphic and structural record that record the complex paleotectonics of the southern California continental margin since the Jurassic.