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Dating the Dunes

Last summer, a few of us at Cherry Republic made an exciting archeological discovery within the Sleeping Bear Dunes National Lakeshore. A day that began with young boys impersonating Indiana Jones (searching for arrowheads while keeping an eye out for the Arch of the Covenant), turned into a plot that would excite Indiana Jones himself.

Just as we were preparing to end our excursion empty handed, Cousin Andrew sauntered past one last dune blowout and noticed an interesting array of what looked to be dry leaves. The array was patterned and looked odd and out of place. So we took a closer look. After further examination Bob concluded that we were looking at fragments of a clay pot!

That evening we excitedly told the Park Service of our find and the very next day we were leading park officials to the site.  The sherds were carefully collected and quietly, the park service has been monitoring the area and has enough evidence to create what they believe will become an important story of the Sleeping Bear Dunes history.

You can read all about our discovery here.

Like any discovery, our find raised quite a few questions like "Hold old is this pot?" and "Which Native American group made it?", etc. So a few weekends ago, the park service brought in several experts from around North America to pinpoint the exact age of the dunes, and therefore, the pottery itself.  What did they find? Let Andrew's photos tell the story..

On the windswept morning of Saturday November 1st, I pulled in to the trail head parking lot that would lead me to the discovery site. The team of scientists I was meeting had been on location since sunrise, plotting, analyzing, photographing, and taking sand samples, all the while developing images in their mind of what this area looked like thousands of years ago. The talented "international" team of geoarchaeology experts included:

  • Dr. William Lovis, Archaeologist, Michigan State University (Dr. Lovis is one of the archaeologists who completed some of the first archaeological surveys of the Sleeping Bear Dunes in the early 1970's.)
  • Dr. G. William Monaghan, Geologist, Indiana University
  • Dr. Andrew Stewart, Archaeologist/Consultant from Ontario, Canada
  • Laura Quackenbush, Sleeping Bear Dunes National Park Curator and Historian
Sleeping Bear Dunes archaeology team The archaeology team. From left, Laura Quackenbush, Dr. William Monaghan, Dr. William Lovis, and Dr. Andrew Stewart.

The goal of the day was simple; collect multiple soil and sand samples from varying depths and locations around the pottery site in order to piece together a chronological story of the history of the dunes.

The story they look to tell is as follows:

  1. The point in time when the area of the pottery find was under lake Michigan.
  2. The point in time when the soil layer near the pottery find covered up the sand.
  3. The age of the soil/tree near the pottery find.
  4. The point in time when the dune overtook the soil layer and covered it completely.

Almost as soon as I arrived, the team surrounded a recent dune blowout and began analyzing the soil layers and striations (seen in the photo below). The scientific verbage they were using seemed fabricated to a simple-minded marketer like myself. At times I swore they were speaking a different language altogether.

DSC_8358 Dr. William Monaghan (foreground) and Dr. Andrew Stewart analyze the layers and striations of the dune blowout.

One thing I could read however, was their emotion. The team seemed genuinely excited and interested in these little knolls of sand and soil.

They immediately noted that the soil layer (the dark layer near the top) will be of particular importance because this would mark the point in time in which humans inhabited this particular piece of land.

DSC_8355 Dr. Bill Monaghan analyzes the composition of a soil sample from the dune blowout.

After a quick visual analysis and a review of the game plan, the team began taking samples. The Bill's began by taking a few general samples from the soil layer. By running a few composition tests they should be able to give a ball park estimate of its age.

Next they needed to answer the question, when was the buried sand, located beneath the soil layer, covered up by other blowing sands?

To answer this, Dr. Monaghan took multiple core samples from deep within multiple surrounding dunes. These samples will enable the team to pinpoint the year when that particular sand dune was covered up by more blowing sand.

Dr. Bill Monaghan hammers a core cylinder into the sand. Dr. Bill Monaghan hammers a core cylinder into the sand.

Around this time, Bob and his two boys came bounding down an adjacent sand dune eager to jump in and lend a hand. Colebrook and Hawthorn were a bit shy at first but excited to be a part of the project.  Bob had a short chat with Dr. Monaghan where the Dr. said he felt that he believes the pottery to be between 1,000 and 1,100 years old. He has seen pottery with similar designs patterns etched into the clay at archaeological sites in other places in the midwest that were from that same point in time.

Each sand sample taken will be tested in a process called thermoluminescence dating. In layman's terms (since that's the only way they could explain things to me and I still understand) the crystalline material in the sands reacts with sunlight and decays at a very specific measured rate so the scientists can pinpoint the last time the particular area of sand came in contact with sunlight.

A core sand sample. This core will be dated to tell when this section of sand was covered by the dunes. A core sand sample. This core will be dated to tell when this section of sand was covered by the dunes.

In order to document each sample taken, Dr. Lovis carefully titled each sample with a unique name which included what the sample contained, and the location from which it was taken.

Dr. Bill Lovis gives the core sample an identifying marker. Dr. Bill Lovis gives the core sample an identifying marker.

Before we packed up our bags and called it a day, Dr. Monaghan told us that he wanted to grab one last sand sample from underneath a rock bed. He wanted to find out when this low area 50 yards away from the dune samples we collected was under lake Michigan.  We weren't sure how deep the rock bed went when we started digging (Colebrook surmised that we might dig to China), but eventually found pure sand 75cm or so below the surface. This sand will be carbon dated and might help us learn where the lake shore was 1,000 or 5,000 years ago.

DSC_8471 Dr. Andrew Stewart digs a deep hole through layers upon layers of rock to reach pure sand in order to take another core sample.

Of course, this whole story began with two small boys excited to become Indiana Jones and make their own discovery. And as the photo below shows, Colebrook and Hawthorn were energized by meeting real life Indiana Jones' and began a new search themselves.

DSC_8467 Bob's boys, Colebrook (in green) and Hawthorn (beige) were excited to be surrounded by "real life" Indiana Jones' and decided to start digging for themselves.

As we we're packing our bags, the team believed they have enough evidence to tell a deeper story of the activity and geology of the past 1,500 years of this area of the dunes.

Remains of flux and charcoal and such lead the researchers to believe that this specific spot in the dunes was a pottery 'factory'.

The next steps in the process are quite simple but will take some time. All of the soil and sand samples will head back to the Midwest Archaeological Center and wait to be tested. After testing, the scientists will connect the dots and piece together a detailed 1,500 year history of our favorite dunes.

Geeze, we can't wait to tell that story!

Everyone we had the pleasure to work with stressed that the Dunes will eventually reveal more secrets, but that those secrets deserve to be protected and shared with generations to come. If you happen to know where the site is located we ask that you please keep it private.

And if you happen to stumble upon such a find, please call the Park Service immediately! Thank You!