Nicole Grabos and Erin Argyilan PhD (Advisor)Department of Geosciences- Indiana University Northwest

Field Methodology of Optically Stimulated Luminescence (OSL) Dating of Parabolic Dunes Along the Southern Shoreline of Lake Michigan

Outline

• Study Background • Site Location • Methodology • Results• Conclusions • Study Accomplishments

Evolution of Parabolic Dune Formation

•What amount of time is preserved in a single dune?

•What is the most reliable age for dune stabilization?

•Can Particle Size Analysis (PSA) be used to observe depositional patterns and locate optimal points of stabilization?

“Field Methods” of OSL

Samples were collected below bioturbation within the C-horizon

PSA was collected from individual horizons to observe changes in grain transport

Optically Stimulated Luminescence (OSL) Dating

• OSL will determine the age of burial on individual quartz grains

• Single-Aliquot Regeneration Methodo Up to 90 aliquots are used to

determine the overall age

• Age = De/Dose rate o Dose Rate: Radiation in the

surrounding soil determined through atomic absorption

o De: Measure of energy accumulated in the grains

Study Design

Study Area: Southern Shoreline of Lake Michigan Toleston Beach Deposits (4500 years old to present)

Sample Site: Inland Dunes • A westerly oriented

parabolic dune was chosen north of Stagecoach Rd. just south of Inland Marsh in Ogden Dunes.

• The dune size is approximately 1720 feet in diameter.

• Total dune relief is approximately 50 feet.

• Sample placement was adjusted due to interference from the adjoining dune to the southeast.

Inland Dunes Results

• Evidence of grading, though a finer resolution is necessary to define grainfall patterns

• Observable differences in ages, though all overlap in error• Bucket-Augering yielded an older sample age

Sample Site: Dune Acres• A easterly oriented

(indicating a south-westerly wind) parabolic dune was chosen just east of Mineral Springs Rd. in Dune Acres.

• The dune size is approximately 2375 feet in diameter.

• Total dune relief is approximately 28.5 feet.

• Sample location was chosen due to well defined shape and minimal interference by surrounding dunes.

Dune Acres Results

• Resolution was not fine enough to see evidence of grainfall patterns

• Observable differences in ages, though all overlap in error• Bucket-Augering yielded an older sample age

Conclusions • Both dunes overlapped in error using the OSL method,

indicating that any part of the lee side would be acceptable for an indication of stabilization

• In both cases, the bucket augured sample yielded an older age, possibly due to muddling of the sample. Therefore, the pit digging method may be a more reliable approximation for stabilization.

• Grading was present in the Inland Marsh sample, though a finer resolution would be necessary to make distinguishable conclusions

• The combination of PSA and OSL revealed that though the dunes were formed at roughly the same period of time, migration history of individual dunes could be interpreted using the PSA

Grant Accomplishments• Formal presentations at both COAS Undergraduate Research

Conference and National Geological Society of America (GSA) Conference

• Experience with ArcGIS mapping software• OSL sample processing in North Dakota State University’s

laboratory • Data was accepted for publication • This data also served to fuel an adjacent study that used the

dune geomorphology, PSA, and OSL to approximate a more accurate point of stabilization based on active dune dynamics

References• National Park Service. "Lake View." Indiana Dunes National

Lakeshore. Spring 2012. Web. Spring 2012.• Sloss, Craig R. "Coastal Dunes Geomorphology." Nature.com. Nature

Publishing Group, 2012. Web. 05 Apr. 2012. <http://www.nature.com/scitable/knowledge/library/coastal-dunes-geomorphology-25822000>.

• Mallinson, D. "Optically Stimulated Luminescence Is a Method of Determining the Age Ofburial of Quartz or Feldspar Bearing Sediments Based upon Principles Ofradiation and Excitation within Crystal Lattices, and Stems from the Fact Thatimperfections in a Crystal Latt." A Brief Description of Optically Stimulated Luminescence Dating. 2008. Web. 05 Apr. 2012. <http://core.ecu.edu/geology/mallinsond/OSL.htm>.