By Catherine Drake, Invertebrate Zoology Lab

The last field trip of the fall semester for the Geological Oceanography class was to the Monterey Formation on Toro Road in the Salinas Basin. As we drove up through the hills on the winding road, we came across a grayish cliff that must have spanned about a mile down the road. The students got out of the car, and as we walked along the road, we noted the striations and laminations within the sedimentary layers. What’s especially interesting about these layers is that they are biogenic sediments: they consist of organic particles, usually in the form of skeletal fragments of marine organisms.

The Monterey Formation consists of an incalculable amount of diatoms, which are a type of phytoplankton and are primary producers, meaning they take up carbon dioxide while. Diatoms have siliceous tests, meaning that their cell walls are silica based; so, when diatoms die, they become part of a siliceous ooze and get deposited on the seafloor. Considering that diatoms usually range from 2 to 200 μm and the Monterey Formation spanned almost a mile, which means that there were hundreds of millions of diatoms at the time! Primary production must have been incredibly high during that time period, which was approximately between 11 and 3 million years ago.