New luminescence rock dating technique to help answer archaeological questions in Lincoln County, Nevada

New luminescence rock dating technique to help answer archaeological questions in Lincoln County, Nevada

Above: In Coal Valley, located in Lincoln County, Nev., dry playas and ancient shorelines of ice-aged lakes hold clues to some of the Great Basin’s earliest inhabitants. DRI archaeologists are working to learn more about these ancient cultures through a new luminescence dating technique. Credit: DRI.


 

Reno, Nev. (Nov 16, 2020) – In Lincoln County, Nev., dry playas and ancient shorelines of ice-aged lakes hold clues to some of the Great Basin’s earliest inhabitants – but assigning precise dates to archaeological artifacts and features buried within the region’s shifting sands and silts has long proved challenging.

Now, with new funding from the Lincoln County Archaeological Initiative managed by the Bureau of Land Management, a group of scientists led by Christina Neudorf, Ph.D. and Teresa Wriston, Ph.D. of the Desert Research Institute (DRI) in Reno will improve our knowledge of Lincoln County’s rich archaeological history by developing and refining a new technique in luminescence dating.

Luminescence dating, which uses light emitted by minerals to date events in the past, is a technique most commonly applied to silt or sand samples. In this project, the research team will apply new methods in luminescence dating to analyze the burial ages of larger rock samples.

“Trying to develop a technique to date the burial ages of rocks will help us better understand the lake levels of the past and when people would have used or settled along these beaches,” said Neudorf, Assistant Research Professor of Geology and manager of DRI’s Luminescence Laboratory. “We think this will be more accurate than dating sand, which often gets reworked and redeposited over time.”

The project involves several phases. Researchers will first conduct fieldwork in Coal Valley, located within the Basin and Range National Monument, to gather rock samples from pre-approved areas close to known archaeological sites. They will then process the samples at the DRI Luminescence Laboratory in Reno by extracting and dating quartz and feldspar from the rock. Finally, the team will analyze their data and produce a technical report detailing enhanced knowledge of lake history and archaeology for the use of future archaeological surveys in Lincoln County. They will also produce a series of videos that summarize the work.

The ability to date rock surfaces using luminescence dating is an exciting advance that will help archaeologists more quickly identify appropriate areas of the landscape for study, Wriston said. Eventually, she hopes to be able to use this technique to date rock art by identifying when the rock surface was covered with paint, or to date when particular artifacts that have been buried were last used or exposed to light.

“This technique will really revolutionize Paleoamerican archaeological studies in the west,” Wriston said. “We know that people used these shorelines; that’s what attracted the earliest people to the Great Basin. This luminescence dating technique will help us build on results of previous work in the Coal Valley area of Lincoln County and give us a more complete picture of the ancient lake history and people’s place in it.”

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The Desert Research Institute (DRI) is a recognized world leader in basic and applied interdisciplinary research. Committed to scientific excellence and integrity, DRI faculty, students, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge, supported Nevada’s diversifying economy, provided science-based educational opportunities, and informed policy makers, business leaders, and community members. With campuses in Reno and Las Vegas, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit  www.dri.edu.

Gault site research pushes back date of earliest North Americans

Gault site research pushes back date of earliest North Americans

Stone tool assemblage recovered from the Gault Site. Credit: Produced by N Velchoff, The Gault School of Archaeological Research.

Luminescence dating confirms human presence in North America prior to 16 thousand years ago, earlier than previously thought

July 20, 2018 (Reno, NV) – For decades, researchers believed the Western Hemisphere was settled by humans roughly 13,500 years ago, a theory based largely upon the widespread distribution of Clovis artifacts dated to that time. Clovis artifacts are distinctive prehistoric stone tools so named because they were initially found near Clovis, New Mexico, in the 1920s but have since been identified throughout North and South America.

In recent years, though, archaeological evidence has increasingly called into question the idea of “Clovis First.”Now, a study published by a teamincluding DRI’s Kathleen Rodrigues, Ph.D. student, and Amanda Keen-Zebert, Ph.D., associate research professorhas dated a significant assemblage of stone artifacts to 16-20,000 years of age, pushing back the timeline of the first human inhabitants of North America before Clovisby at least 2,500 years.

Significantly, this research identifies a previously unknown, early projectile point technology unrelated to Clovis, which suggests that Clovis technology spread across an already well-established, indigenous population.

These projectile points are unique. We haven’t found anything else like them,” said Tom Williams, Ph.D., Postdoctoral Research Associate in the Department of Anthropology at Texas State University and lead author of the study. “Combine that with the ages and the fact that it underlies a Clovis component, and the Gault site provides a fantastic opportunity to study the earliest human occupants in the Americas.”

The research team identified the artifacts at the Gault Site in Central Texas, an extensive archaeological site with evidence of continuous human occupationThe presence of Clovis technology at the site is well-documented, but excavations below the deposits containing Clovis artifacts revealed well-stratified sediments containing artifacts distinctly different from Clovis.

Diagram of soil layers identified at the Gault Site.

To determine the ages of these artifacts, Rodrigues, Keen-Zebert, and colleagues used a process called optically stimulated luminescence (OSL) dating on the sediments surrounding them. In OSL, researchers expose minerals that have long been buried under sediment layers to light or heat, which causes the minerals to release trapped potassium, uranium, and thorium electrons that have accumulated over time due to exposure to ambient, naturally occurring radiation.When the trapped electrons are released, they emit photons of light which can be measured to determine the amount of time that has elapsed since the materials were last exposed to heat or sunlight.

“The fluvial nature of the sediments deposited at the Gault Site have created a poor environment for preservation of organic materials, so radiocarbon dating has not been a useful technique to apply in this region,” said Kathleen Rodrigues, graduate research assistant in DRI’s Division of Earth and Ecosystem Sciences. “This made luminescence dating a natural choice for dating the archaeological materials here.  We are really pleased with the quality of the results that we have achieved.” 

The study was published on July 11th in the journal Science Advances and is available here: https://advances.sciencemag.org/content/4/7/eaar5954.

For more information on DRI’s optically stimulated luminescence dating capabilities, visit https://www.dri.edu/luminescence-lab

Jayme Blaschke of the Texas State University Office of Media Relations contributed to this release.

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The Desert Research Institute (DRI) is a recognized world leader in investigating the effects of natural and human-induced environmental change and advancing technologies aimed at assessing a changing planet. For more than 50 years DRI research faculty, students, and staff have applied scientific understanding to support the effective management of natural resources while meeting Nevada’s needs for economic diversification and science-based educational opportunities. With campuses in Reno and Las Vegas, DRI serves as the non-profit environmental research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.