The work of John Bluemle PhD

2-INTRODUCTION TO NORTH DAKOTA GEOLOGY – PART TWO

Turtle Mountain erratics

Fig. 2-A. Slopes on the south side of Turtle Mountain in Bottineau County, in an area where glacial erratic boulders are abundant. Erosion by running water, flowing on the surface along the slope of the Turtle Mountain upland has removed much of the fine materials, leaving erratics concentrated on the surface. Photo: 8-31- 2010.

Glaciation was the main geologic influence on much of North Dakota’s landscape. The Ice Age, a time geologists also refer to as the Pleistocene Epoch, includes most of the past three million years of geologic time. Glaciers advanced over the northern plains several times during the Ice Age,  reaching northern and eastern North Dakota. When it wasn’t glaciated, the state had a climate much like the one we enjoy today or possibly even milder at times. the Ice Age wasn’t one long “deep-freeze.”

Little Missouri River, wind canyon

Fig. 2-B. Badlands along the Little Missouri River in Billings County. Rapid erosion by the river causes the poorly consolidated sandstone and siltstone layers of the Bullion Creek Formation to slide downward, resulting in steep, freshly exposed slopes. The water carries these materials away when they fall into river, starting them on their way to the Gulf of Mexico. Photo: Photo: 9-16- 2009.

 

 

 

 

 

During their studies of the geology of the state, geologists have found evidence for at least seven separate glaciations, but there may have been more. The most recent of these glaciations is known as the Wisconsinan (because deposits typical of that glaciation are widespread in Wisconsin). The Wisconsinan glaciation began about 100,000 years ago and ended about 11,000 years ago. Some geologists debate whether the Ice Age has really ended yet. After all, large areas of the earth’s surface are still covered by extensive glaciers (Greenland, Antarctica, etc.). It’s likely that we are currently enjoying a lull between major glaciations.

Even though North Dakota was glaciated many times during the Ice Age, it is the Wisconsinan glacial deposits, the most recent ones, that are most obvious to us. These are the ones that form the hills and valleys in eastern and northern North Dakota and they are the ones in which our prairie potholes and wetlands are developed. Most of our richest farmland is developed on the Wisconsinan glacial surface.

Early glaciers, which advanced into North Dakota before the Wisconsinan glacier, also had a profound effect on the state. The materials they deposited have been largely eroded away, and about all that remains of them are occasional boulders  — “erratics.” I will discuss erratics elsewhere. It was an early glacier that diverted the course of the Little Missouri River eastward more than 640,000 years ago (possibly earlier). Before that time, the Little Missouri River flowed northward into Canada. In fact, all of North Dakota used to be drained by rivers that flowed into Canada. When it was diverted, the Little Missouri River began to carve the badlands we see today.

Blue Buttes, near Keene ND.

Fig. 2-C. Blue Buttes area of McKenzie County, near Keene. This butte, and others near the south end of a grouping known as the “Blue Buttes,” is capped by a sandstone layer of the Eocene Golden Valley Formation (the caprock is barely visible, along the top of the butte). Many of the larger buttes in this part of the State are capped by the same sandstone bed. The view is toward the west, with a thunderstorm approaching. Photo: 7-27- 2010.

All of us who have traveled around North Dakota know that the landscape varies considerably from place to place. Southwestern North Dakota, with its badlands, buttes, and broad vistas is largely the result of hundreds of thousands of years of erosion. The landscape there is not glacial. It has been carved from layers of flat-lying sandstone and other materials.

The Missouri River marks an approximate boundary between the eroded landscape of southwestern North Dakota and the entirely different glacial landscape north and east of the river, where we see small hills – small at least compared to large buttes like Sentinel Butte and Bullion Butte found in southwestern North Dakota. Eastern North Dakota is characterized by thousands of potholes, poorly developed drainage in places, and remarkably fertile farmland.

When the glaciers advanced over the state, they picked up some of the materials over which they flowed. The glaciers contained a variety of kinds of soil and rock, which they eventually deposited as thick layers of sediment. The exposed surface of these sediments has been weathered for the past several thousand years (since the glaciers melted) and it forms the rich soils our farmers work today.

Lake Sakakawea till, glacial deposits

Fig. 2-D. Glacial deposits (till) exposed in bluffs along Lake Sakakawea near Riverdale. This 40-foot-high cliff exposes boulders incorporated in a mass of finer material – the overall mixture is referred to as “till” by geologists. Most of the till shown here – the part that is characterized by vertical partings – was deposited by a glacier during Early Wisconsinan time, about 70,000 years ago. Younger, Late Wisconsinan till, about 16,000 years old, lies on top lighter color, lacking vertical partings and immediately beneath the grass cover. Photo: 6-27-2009.

Over much of eastern North Dakota, the glacial sediments were laid down as an undulating plain (think of the Carrington, Finley or Kenmare areas, for example). In other places, a more hilly landscape resulted (think of Turtle Mountain or the Missouri Coteau — places like Belcourt, Hurdsfield, Max, Ryder and countless others). In still other places, water from the melting glacier became ponded, forming huge lakes. Today, most of these areas are flat. Examples of the flat topography may be seen in places like Fargo, Hillsboro, Grand Forks or Grafton. The old floor of Glacial Lake Agassiz (the Red River Valley) is the classic example of flat. Hundreds of smaller glacial lake plains are found in North Dakota too.

Dead-ice moraine on Missouri Coteau

Fig. 2-E. Dead-ice moraine topography on the Missouri Coteau, about five miles north of Palermo, Mountrail County. The road helps to show the relief. Photo: 7-2-2010.

 

 

 

 

 

As the glaciers flowed over North Dakota, they tended to smooth off and wear down the hill tops and fill in the lower areas with sediment. The overall result is a fairly level landscape. The layers of glacial sediment underlying that landscape are extremely complex, containing buried river channels, blocks of sandstone and shale, old landscapes that were covered many times by fresh glacial sediments. Buried layers of gravel and sand, deposited by water flowing from the melting glacial ice, constitute aquifers. They contain some of our best sources of fresh water.

As the ice flowed, in some places it picked up large chunks of material and moved them short distances before setting them down again. A good example of this is at Devils Lake, where a large amount of material was picked up and moved southward a few miles. Today, Devils Lake lies in a broad lowland. South of the lake is a high range of hills, including Sully’s Hill. The hills consist of materials that were once in the lowland where Devils Lake is now.

In some places, huge floods of water from melting glaciers carved deep river channels. Countless small meltwater valleys, along with some large ones too, are found throughout eastern and northern North Dakota. The Sheyenne, Souris, and James River valleys are good examples of large meltwater valleys. Valley City, Minot, and Jamestown are nestled in meltwater valleys. The Missouri River valley is another example of a glacial river channel, but it had such a complicated history that I’ll plan on writing a special article about it.

How thick were the glaciers that covered North Dakota? Certainly, they were more than a thousand feet thick in the east and north, so thick that the Earth’s crust beneath the ice buckled and sagged downward, eventually rebounding when the ice melted.

Baldhilll Creek, glacial meltwater channel

Fig. 2-F. Baldhill Creek in its meltwater valley about three miles south-southeast of Hannaford in southern Griggs County. This is an example of a very small stream flowing in a valley that is much too large for the size of the stream (an “underfit stream”). The valley was formed by a much larger flow of water from melting glacial ice. Photo: 6-29-2011.

Who or what lived in North Dakota during the Ice Age? Mastodons and wooly mammoths lived along the edge of the glacier. Elk, caribou, and horses were common. Horses became extinct in North Dakota  and in  North America at the end of the Ice Age, They survived, worldwide, because they had migrated to Asia via the land bridge between North America and Asia prior to then. During my field work over the years, I’ve found mastodon teeth, caribou bones and, in the Lake Agassiz deposits, fossil fish bones, mainly perch. It’s likely that early humans also lived here while the most recent glacier was still melting.

I’ve mainly been discussing North Dakota’s glacial landscape. Part of the state, the southwest quarter, was not glaciated, but the glaciers also left their mark there. The badlands along the Little Missouri River owe their existence to early glaciers that diverted the river eastward from its northerly route into Canada. This diversion triggered greatly increased erosion by the Little Missouri River, which resulted in the formation of badlands.  Some places that were not glaciated are marked by polygons, formed when permafrost froze the land beyond the limit of the glaciers.

Sheyenne River; meltwater channel, erratics

Fig. 2-G. Sheyenne River meltwater channel (a small part of the valley) about six miles southeast of Cooperstown in southern Griggs County. Notice the large number of glacial erratic boulders on the slopes of the valley wall. Erratics remain behind when erosion by the running water removes the finer materials (silt, clay, etc.). Photo: 6-29- 2011.

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