An oxygen and carbon isotopic stratigraphy has been established for the Miocene Monterey Formation (∼18 to 8 Ma) at Naples Beach, Santa Barbara County, California. Correlation to the deep-sea climatic record provides a test of the Monterey hypothesis, which suggests that organic-carbon-rich deposition in the Monterey Formation fostered middle Miocene global cooling through drawdown of atmospheric partial CO2. Oxygen isotopic correlation of the Naples Beach section to the deep-sea record suggests that increased organic-carbon-rich deposition coincided closely with deep-water cooling and major East Antarctic ice-sheet growth from 14.5 to 14.1 Ma and with a δ13C maximum in deep-sea records. These results support a corollary of the Monterey hypothesis, that episodic organic-carbon-rich deposition within the Monterey Formation contributed to deep-sea δ13C maxima and to synchronous global cooling.

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