Geochemistry of coastal tarballs in southern California—A tribute to I. R. Kaplan

In the southern offshore California borderland, natural oil seeps occur mainly in the Santa Barbara Channel and Santa Monica Bay. Coastal tar residues (tarballs) from beaches bordering these water bodies were analyzed for six geochemical parameters: stable carbon isotopic compositions (δ¹³C) and four biomarker ratios (C₂₈IC₂₉ hopane, sterane/hopane, refractory index, bisnorhopane index), and the presence or absence of trisnorhopane. The objectives of this study were to group these residues and infer possible sources and transport directions. Three major groups were established. Two groups are likely from natural seeps near the Channel Islands, whereas the third group probably comes from seeps within Santa Monica Bay. Residues from all groups occur on the Channel Islands and on mainland beaches from as far south as San Diego to Point Reyes north of San Francisco.