Miocene Laird Sandstone and Monterey Formation, Kehoe Beach,
Point Reyes National Seashore, California


ID 2980

The middle Miocene Laird Sandstone (foreground) is transitional into the overlying Monterey Formation (background), which consists of alternating thin-bedded and laminated siliceous mudstones, cherts, porcellanites, micaceous siltstones, and fine-grained sandstones. The Monterey Formation contains may single-celled organisms (foraminifera and diatoms) as well as fish scales and plant material. The thin bedding and scant evidence of benthic organisms in the Monterey sediments suggests that it was deposited in very deep water where little oxygen was available to support animal life. This Laird-Monterey section records progressive deepening after transgression of the middle Miocene seas.

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