Building a fossil inventory for Colonial National Historical Park in 2020

Cornwallis Cave in Yorktown, Virginia. The entrance, at lower left, is closed to the public because of safety concerns. NPS photo by Mackenzie Chriscoe.

The first comprehensive inventory of fossils at Colonial National Historical Park (COLO), Virginia, began in 2020, and a college intern worked on it while the pandemic pushed the lab work out of the university. This article from the Park Service’s Park Paleontology News (Fall 2020) was written by Mackenzie Chriscoe, then a rising senior at William & Mary, who joined the project as an intern in January 2020. The intern’s words are paraphrased here.

The project

The inventory came out of a partnership between William & Mary geologist Dr. Rowan Lockwood and a team of NPS employees, principally Vincent Santucci, Justin Tweet and Dorothy Geyer. It was to end in an inventory and in a senior thesis presented to William & Mary’s geology department. The first job, in January, was a literature review: tracking down all information about local fossils and where they had been found in COLO, and starting a taxa list from past studies. By June the field work began. Chriscoe led several excursions with Lockwood, sometimes joined by other geology majors, to collect bulk samples of fossils and sediment, which were later sieved and sorted to identify species and describe the sediment.

Float collected from a study site in Yorktown, Virginia. Photo courtesy of NPS, Mackenzie Chriscoe.

A park where history and geology meet

COLO was created to protect sites of key battles of the American Revolutionary and Civil Wars, along with other historic places such as Jamestown, the first permanent English settlement in North America. Fossil collecting in and around the park goes back to the 17th-century settlers at least. The oldest fossils in the park are from the Miocene and can be upwards of five million years old.

The geology is complex, and no single cliff or outcrop preserves the whole sequence. Changing sea level created several scarps, and some buried faults may have been caused by the Chesapeake Bay Impact Structure, a crater from an extraterrestrial impact around 35 Ma that lies under part of the park. The crater could also help explain the complexity of the layers.

Cornwallis Cave

The park’s most interesting geologic feature, in the author’s view, is Cornwallis Cave, a small human-made cave cut into a cliff of cemented shell hash. It was supposedly a refuge for General Cornwallis during the Revolutionary War, although that is frequently debated because of historical inconsistencies in the cave’s location and size. It was certainly used for food storage in the 18th and 19th centuries and played a role in the Civil War. Because the cliff is made of shells, it reacts to chemical weathering, which is unusual where carbonate deposits are scarce. The Park Service wants to preserve the site and to understand how to manage natural processes such as rain and groundwater erosion acting on it. The cave does little for the fossil inventory, but whole shells and a few preserved burrows can be seen in the cliff face, and the burrows help reconstruct the geologic past.

Working through COVID-19

The pandemic changed how the work was done. Instead of the Paleontology Lab at William & Mary, much of the sorting happened at home, which also limited access to Lockwood and made identifying samples slower. The intern shared pictures with tentative identifications in an online folder for Lockwood to confirm. Field work followed William & Mary’s guidelines: everyone wore masks and kept six feet apart, which was hard when bulk samples needed two people to carry. Temperatures were regularly above 90 degrees Fahrenheit with 100% humidity. The lab group added its own rules of plenty of water and ice cream, and the author thanks the NPS, the geology department and the lab group for making the project possible.

Sources

• Mackenzie Chriscoe (William & Mary), Counting Fossils in Colonial Virginia During COVID-19, Park Paleontology News, Vol. 12, No. 2, Fall 2020, National Park Service; rewritten in hubnx's own words.