The Science of Sustainability

New Fossils from the Caldecott Tunnel

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caldecot tunnel fossils"Paleo mitigation" work during the dig of the new Caldecott Tunnel bore has yielded fresh insight into a familiar set of rocks thanks to fossils like this Miocene horse molar. All photos courtesy CalTrans and PaleoResource Consultants.

The fourth bore for the Caldecott Tunnel, which connects Oakland and points west with Orinda and points east, is being dug day and night with the first drive-throughs slated for 2013. Part of the job is what Caltrans contracts call "paleontological mitigation": allowing fossil scientists to salvage resources—"fossils and the deposits they are found in"—that would otherwise be destroyed. A paleo mitigation agreement governs the Caldecott fourth bore project, and scientists shared some of the early results earlier this month.

Fossil hunting is tedious, exacting work, but there are those who love it. Kristin McCallister, a paleontologist for contractor PaleoResource, is shown here during early work at the job site, examining spoils.

paleontologist

The vast majority of fossils are microscopic and consist of plankton or pollen grains. But the big bones are sexy. Let's look at the pictures PaleoResource's Lanny Fisk showed at the CalPaleo 2011 meeting in Rocklin, starting with the leg bone of a rhinoceros.

caldecott rhino

Here are two vertebrae of a Miocene camel species.

caldecott camel

And this is the metatarsal bone of an ancient horse.

caldecott horse

Finally here's the upper jaw of an oreodont, an extinct browsing mammal the size of a sheep.

caldecott oreodont

All of these (plus bird, pronghorn and wolverine bones) were salvaged from rocks of the Orinda Formation that are about 11 million years old, a time late in the Miocene Epoch. The researchers also found hundreds of plant fossils for the first time in these rocks, including this laurel leaf.

caldecott laurel

The Orinda Formation makes up the eastern end of the bore. In the middle is the Claremont Formation, a cherty unit that holds up the highest part of the Berkeley Hills. This 1-inch clam is from the Claremont.

caldecott clam

Obviously this shows a change from a land to a sea environment as we go back in time.

At the west end of the bore is the still older Sobrante Formation. Fisk told the CalPaleo audience that this unit has yielded a large fish fossil fauna as well as some leaves and marine invertebrates (clams, crabs and plankton). He was particularly excited about the fish, which somewhat resemble cool-water fish of this age from northwestern Oregon.

One handicap that Fisk mentioned was difficulty getting into the tunnel, where paleontologists can watch the rock face and stop operations long enough to examine and salvage the best fossils. Working the spoils pile isn't good for getting exact locations and geological context for fossils. But the bore will be carried out in two passes, and maybe we can get another look at this unique dig.

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Category: Geology

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Andrew Alden

About the Author ()

Andrew Alden earned his geology degree at the University of New Hampshire and moved back to the Bay Area to work at the U.S. Geological Survey for six years. He has written on geology for About.com since its founding in 1997. In 2007, he started the Oakland Geology blog, which won recognition as "Best of the East Bay" from the East Bay Express in 2010. In writing about geology in the Bay Area and surroundings, he hopes to share some of the useful and pleasurable insights that geologists give us—not just facts about the deep past, but an attitude that might be called the deep present. Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.
  • Jcr1929

    I found this very interesting but what was the first item 4.5 cm long and how do they know from such small samples what they are? none appear to be very large. 2n d question what signifies the Sobrante Formation & is it seperate from the Orinda or Moraga formations and what time frame is in in? JCR

  • Barbara

    Fascinating !