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Quarry Geology: Fossils from Florida May Forecast Our Future

by Adam Blankenbicker -- Apr 6, 2016
Photo of Adam Blankenbicker, a geology education specialist at the Museum

Adam is a self-proclaimed “volcanologist-turned-educator” who enjoys designing visitor experiences, especially around, you guessed it, geology. He has led...

Lake at Golden Gate Quarry. Photo by Don Hurlbert, Smithsonian.
Lake at Golden Gate Quarry. Photo by Don Hurlbert, Smithsonian.

I recently had the opportunity to travel with five geologists to unique sites around the country to understand more about the diverse geologic history around us. We were observing rocks and landscapes to reveal evidence of what happened in Earth’s past. Each of these geologic sites was located at an active rock quarry. My travels took me to Naples, Fla., with Smithsonian Marine Geologist Maggie Toscano, who showed me Golden Gate Quarry, a quarry of fossils.

When most people think of a quarry, they think of rocks. It’s true that many quarries mine rocks; every day we see building stones, roads and bridges, marble and granite surfaces, and even statuary and monuments. But quarries also mine tremendous quantities of unconsolidated material such as industrial sand and gravel. At Golden Gate, I found myself at a unique quarry that produces marine fossil shells and corals, mainly used to build roads.

Image iconadam-and-maggie-drag-line.pngDriving through the entrance, I was amazed to find giant piles — 20, 30, and 50 feet high — of fossil corals and shells of gastropods and bivalves. Looking around, however, I did not see the large, exposed cliff faces typical of mining, only a large, blue lake. Here, workers mine fossils from below using a “dragline” system that scrapes the fossiliferous sediment from the sides of groundwater-filled ponds created by the digging.

Why are these ocean fossils here on land? Maggie observed, “Finding shallow marine fossils on land areas tells us that sea level was considerably higher. Also, the species of mollusks and corals tell us that the sea here was warmer than the present day.”

As a geologist I know that, over geologic time, sea level has risen and fallen 100 meters or more during major climate cycles when ocean temperatures have changed. How long ago are we talking about? Maggie explained that the youngest fossils found at Golden Gate are from a known warmer interval during the Pliocene epoch, about 3.2-5.3 million years ago.

Florida is already a hot place today, as our sweating attested. Could it have been even warmer in the past? Maggie said, “Even though Florida is warm today, it was even warmer just a few million years ago, allowing tropical lifeforms to live further north. The fossils here are being mined from ancient, shallow, seafloor deposits similar to modern tropical lagoons of the Caribbean.”

I wondered whether, as climate continues to warm today, tropical species of mollusks, bivalves, and coral will find their way north again. “Most likely,” she said. “Eventually, if modern climate reaches Pliocene-level warmth, tropical species will be able to survive in warming waters further north, even beyond Florida.”

Fossils collected from Golden Gate quarry. Smithsonian photo by Don Hurlbert.Will the warmer waters affect living conditions for these species? “Yes. Warmer waters lead to ocean acidification, which has been shown to inhibit calcification of shells and corals, possibly limiting their viability,” warned Maggie.

So, sites like the Golden Gate Quarry provide insights into the Earth’s past and future. When the Golden Gate quarry fossils lived, sea levels were 5-6 meters higher than today. Evidence from the geologic past helps us forecast what the future may look like under extreme climate change.

See fossil GASTROPODS and BIVALVES in the Q?rius Collection Zone. Get a printable poster about this quarry story. Get a Journey in Time through Quarries poster that shows five geologists and the geologic histories they explore.

 

Categories: Q?rius News, Field Notes