| This dissertation explores the sedimentary record of climatic and environmental change along the tectonically active northern California margin during late Pliocene and early Pleistocene time (ca. 3 to 0.8 million years before the present). Two sedimentary sequences providing expanded and well preserved depositional records were studied: the outer shelf to nonmarine Merced Formation (exposed in sea cliffs near San Francisco) and the slope to outer shelf Rio Dell Formation (exposed in sea cliffs north of Cape Mendocino). A variety of techniques were used to address questions about the paleoenvironmental histories of the two formations: qualitative analysis of sedimentary structure, texture, and composition; benthic foraminiferal assemblage analysis; stable isotopic analysis of benthic foraminifer tests; organic geochemical analysis of sedimentary hydrocarbons; and palynological analysis.; In both formations, previous researchers noted some form of sedimentary cyclicity. Periodic concretionary layers and distinctive shell lags were seen in the fine-grained sediments of the Rio Dell Formation, while repeated sequences of shelf, nearshore, and nonmarine sedimentary facies were identified in the Merced Formation. My research suggests that most sedimentary cyclicity found within the two formations is synchronous with global glacial-interglacial cycles. However, several environmental proxies (the occurrence and abundance of macrofossils and bioturbation, benthic foraminiferal assemblage, gem-dialkylalkanes, and redox indicators) in the Rio Dell Formation appear to vary at a lower frequency, apparently unrelated to changes in global ice volume. This lower frequency variation may be associated with changes in the relative contribution of less oxic Southern Component Intermediate Water off the coast of northern California.; Proxies for a variety of organic inputs into the sediments of the two formations were explored, including: higher plant markers (n-alkanes, steroids, sesquiterpenoids, diterpenoids, triterpenoids), fungal markers (perylene), chemolithoautotroph markers (gem-dialkylalkanes), combustion markers (polycyclic aromatic hydrocarbons), and gas or petroleum seep markers (carbon isotopes, petroleum biomarkers). Several of these proxies are extremely sensitive to variations in specific organic inputs---some markers may even be specific for particular families of higher plants. However, in some cases, the preservation of these markers appears to be heavily influenced by conditions during deposition and early diagenesis. |
