Nature
The Monterey Formation is a vast Miocene sedimentary unit in California, exposed across parts of the Coast Ranges, the Peninsular Ranges, and some offshore islands near its type locality by Monterey. Formed mostly between about 16 and 7 million years ago, it records changing ocean upwelling, deep marine deposition, and later tectonic uplift. Its siliceous and calcareous rocks, derived from microscopic marine organisms, became diatomite, porcelainite, and chert. It is the chief source rock for most of California’s conventional oil, especially in the San Joaquin Basin, though modern shale-oil hopes have been limited by its intense deformation. It also preserves important marine fossils, including rare non-calcareous algae.
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Laguna Hills, California · United States
