SEA LEVEL HISTORY, TECTONICS, AND NUCLEAR POWER: PETE BIRKELAND’S ADVENTURES ON THE MALIBU COAST, LOS ANGELES COUNTY, CALIFORNIA

An early application of Pete Birkeland’s understanding of the time significance of soils led him to a pioneering analysis of the interplay of marine terraces, fluvial deposits, eustatic sea level variation and local tectonics. He was enlisted by Carl Wentworth, a Stanford classmate recently hired by the U.S. Geological Survey, to help use soils to constrain the age of faulting at a site proposed for a nuclear power reactor in Malibu, California. The reactor was never built, but Pete went on to a careful study of the marine terraces, published in 1972 in the Journal of Geology (v. 80, p. 432-448). He mapped the marine and stream terraces, determined their elevations, and devised elegant graphical depictions. He recognized the glacioeustatic component in the geomorphic record by noting the similarity of the elevations of marine terrace shoreline angles with the elevations of the tops of fluvial, fill terraces at the mouths of the stream valleys. These he correctly interpreted to represent interglacial periods, whereas the glacial periods were represented by periods of stream valley downcutting. Three interglacial, high-sea stands were represented by the Malibu, Corral, and Dume (oldest to youngest) marine terraces and their correlative stream terrace deposits. Pete pointed out the similarities between ages of terrace fossils, from the newly developed uranium-series dating method, in California and elsewhere, particularly Barbados and New Guinea. Using age estimates of the Malibu terraces, Pete calculated approximate rates of uplift of the coast, the first such attempt along the Pacific Coast of the Americas. Pete correctly concluded that California marine terraces and the reef terraces on Barbados and New Guinea had a common eustatic origin and their different elevations resulted from different rates of uplift. This important conclusion has withstood the test of time, and stands as testimony to Pete’s careful field work, skillful graphical presentations, knowledge of the global sea level literature, and sound geomorphic reasoning.