Projects designed, Team Jurassic Utah begins fieldwork

May 18th, 2018

Santa Clara, Utah — Galen Schwartzberg (’19) and Ethan Killian (’19) now have their specific Senior Independent Study topics, and so today we began to collect data and specimens. This is always a special time because students have so many possibilities they must narrow down to testable hypotheses that we can practically pursue. Galen is now working on the sclerobionts (hard substrate dwelling organisms) of the Carmel Formation (Middle Jurassic) to compare them to global equivalents, and Ethan is looking at the distribution, shape and size variations, and construction of ostreoliths (“oyster balls”).

Our day began with a delightful meeting in Gunlock. Jay Leavitt (in the overalls) and Judy Leavitt (in red) showed us many local rocks and fossils, and helped us navigate the ownership of the land in our study area. They had great stories about life in Gunlock, and many observations of the local geology. They own and operate a gravel pit, so rocks are a way of life for them. They were very generous with permissions and advice. We hope to see them again on this expedition. (Photo by Nick.)

Ostreoliths and their stratigraphic contexts were the main research topics today in the field. Within a few minutes of arriving at our primary ostreolith site near Gunlock (C/W-157), Nick found these four oyster balls nicely lined up in an outcrop. These are in situ, meaning they are in place in the rocks, not rolled down the slopes like most oyster balls in the field. This meant we could plot out the single horizon of ostreoliths and place it in a stratigraphic column. Nick saved us much work by finding the critical exposure right away. (One, I must add, I walked by without seeing many times.)

The terrain is a bit difficult for stratigraphic description (or I’m getting more wobbly on steep slopes), but we set to work making a column. Here I’m showing how to measure a section with a Jacob’s staff (the striped pole behind me). This section has significant covered parts, so we used the contact with the overlying Iron Springs Formation as our datum. The beautiful yellow-red limestone behind us is designated 157-2. (Photo by Nick.)

Here is the stratigraphic section. Ethan (the student standing lowest on the slope) is at the ostreolith horizon. The thick conglomerate at the top is the Iron Springs Formation base.

Here’s a close view of the cross-bedded limestone unit 157-2. The Jacob’s staff is divided into 10 cm intervals. (Photo by Galen.)

That resistant limestone now known as unit 157-2 has the best trace fossils and ripplemarks in the Carmel, and it is less than a meter thick.

At the end of the day Ethan and Galen began measuring the primary dimensions of the oyster balls, starting at the western end of our sampled horizon and working east. This way they not only will have lots of size data, they can see if there is a gradient of shape and size change. Stay tuned for results.

A Folklore Footnote: Jay Leavitt showed us these flattened limestone clasts that erode out of the Iron Springs Formation basal conglomerate in the Gunlock area. He said that as kids he and his friends called them “Devil’s Dollars”, which they believed had “dark and mysterious powers”. This must be a universal childhood legend that takes many forms. For me the currency was old tiles carefully excavated from a dump in my hometown. Jay told us what Devil’s Dollars were really good for — skipping across ponds!

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