Discovering Hidden Treasures: A Journey through Leelanau Peninsula’s Lighthouse West Natural Area

 By Steven Wade Veatch

Leelanau’s Ice Age history is on full display in the Lighthouse West Natural Area. This 42-acre conservation area, with 640 feet of cobble strewn shoreline along Lake Michigan, is on the tip of the Leelanau Peninsula.  It is near Leelanau State Park, which has a lighthouse. This preserve, although it has “lighthouse” in its name, does not have one. The Leelanau Conservancy established the preserve in 2004, and it is known for attracting birds that stop for food and rest during their migration to nesting grounds farther north (DuFresne, 2021; Lighthouse West website). A 1.2-mile trail, built in 2009, crosses various habitats and geological features.

Much of the Lighthouse West Natural Area’s trail goes through dense woodlands.
Photo date August 2023 by Shelly Veatch.

First, the trail enters an old orchard with pear and apple trees. Patches of wild raspberries and blackberries are profuse there. 

Next, the trail enters the woods and then goes along the edge of a steep bluff with views of the hardwood forest below. You can hear the wind stir the tree leaves. The waves of nearby Lake Michigan crash on the shore and echo through the forest. The air is alive with birdsong and filled with the scent of flowers, forest, and earth.

The trail descends the bluff via a steep stairway and levels off on a boulder terrace shaded by maple and beech trees. Lake Michigan, when it was about 20 feet higher than it is today, created the terrace. This area displays these ancient lake levels and wave-cut bluffs. As glaciers receded, they deposited the boulders. The ice was gone by 10,000 years ago (Fagan, 2009). 

Boulders of various sizes, deposited by receding glaciers,
are along the stairs and trail. Photo date 2023 by Shelly Veatch.

Soon the trail goes around a large glacial erratic, the size of a compact car. This boulder is a felsic granite with small phenocrysts of garnet (almandine-spessartine series). Glacial erratics of all sizes are strewn along the trail. 

A large boulder or glacial erratic, carried by Ice Age glaciers,
was dropped here when the ice melted. The boulder is made of granite.
Photo date 2023 by Shelly Veatch.

Closeup of a freshly broken surface of the large granite erratic.
Note garnet phenocryst (approximately 1 cm) circled in red.
Photo date 2023 by Shelly Veatch.

The trail reaches a viewing deck with a bench, and then a final stairway descends from the ancient lake level to the current shoreline of Lake Michigan. Large boulders, also left by Ice Age glaciers, are present near the shore. The boulders are a variety of sedimentary, igneous, and metamorphic rocks. Limestone erratics preserve different kinds of Paleozoic fossils.

The Lake Michigan shoreline is a cobble beach.
The boulders and cobbles were released here by melting glaciers.
Photo date 2023 by S. W. Veatch.

A large Paleozoic limestone erratic has impressions
of coiled ammonoid fossils. Photo date 2023 by S. W. Veatch. 

This stretch of Lake Michigan’s shoreline conveys an air of tranquility, untouched by the bustling currents of urban life. This quiet, uncrowded, and remote place unveils a canvas of pristine landscapes. The waters here lap against a cobble beach, and their rhythmic whispers harmonize with the rustling leaves, creating a haven of peace for those fortunate enough to visit this remarkable place. 

References and further reading

DuFresne, J., 2021, The Trails of M-22, Michigan Trail Maps, Clarkston, MI.

Fagan, B., 2009, The Complete Ice Age: How Climate Change Shaped the World, Thames & Hudson, London.

Lighthouse West Natural Area Leelanau Conservancy: Retrieved from

https://leelanauconservancy.org/naturalarea/lighthouse-west-natural-area/ on 08/11/2023.

A Glacial Erratic in the Krumwiede Forest Preserve

 By Steven Wade Veatch

The immense limestone rock (in figure 1) looks out of place, sitting on a prominent ridge in the Krumwiede Forest Reserve in Leelanau County, Michigan. That's because it is—during the Ice Age an advancing ice sheet plucked this rock from the bedrock it was moving over and absorbed it into its base. The stony mass slowly rode along, inch by inch, in the glacial ice that had grabbed it. When the climate warmed, some 12,000 years ago, the ice began to melt and recede (Hooker, 2014). Finally, the glacier ice released this boulder from its icy grip and dropped it on this spot in the Krumwiede Forest Reserve. 

Figure 1. This weathered erratic, about midway on the Ridgeline Trail, most likely came from Canada. Moving ice transported this large boulder during the Wisconsin glaciation around 12,000 years ago. Photo date October 2022 by Shelly Veatch.

Geoscientists call this rock a “glacial erratic.” These erratic rocks, whose compositions don’t match the local bedrock where they are found, range in size from cobbles to enormous boulders. Melting ice also dropped till, an unsorted and unlayered mixture of sand, gravel, and rocks of varying size and shape, that is scattered throughout the local landscape. Early settlers gathered boulders left by the glacier to build foundations for their homes.  

Figure 2. An ice sheet, about one mile thick, once covered Michigan. Image Credit: Alexandria R. Baszler. Courtesy of the Institute of Water Research at Michigan State University. https://iwr.msu.edu/kht/TrailSites/5_Glacial_Landscapes.html

The Krumwiede Reserve, part of the Leelanau Conservancy, is in the western part of Cleveland Township. A trailhead is located on Wheeler Road, south of M-22 (figure 3). The 1.6-mile Forestry Loop climbs and crosses a hill (a moraine left behind by a retreating glacier nearly 12,000 years ago) and then descends into a beautiful valley on the other side. The Forestry Loop trail then climbs back up onto the moraine to create a loop. There is evidence of glacial till scattered along the old forest road that now serves as the trail. Wheeler Road occupies a valley where a river of melting ice flowed between two high moraines (DuFresne, 2021). 

Figure 3. Tail map of the Krumwiede Forest Reserve. The property is in its natural, forested condition. Courtesy of the Leelanau Conservancy. 

To see the erratic, start on the Forestry Loop trail in the parking area (figure 3). Head south. Near a ridge (after 0.4 miles), take the narrow Ridgeline Trail footpath north (or turn left) to reach the erratic, which is situated halfway along the trail. This rustic path follows the top of the ridge for about .03 miles before reconnecting to the Forestry Loop trail. Turn left at the Forestry Loop trail to return to the parking lot.

Ice sheets from the last Ice Age left their calling cards in the form of boulders on Michigan’s landscapes. Today, these rocks engender wonder when they are encountered.

References and further reading:

DuFresne, J., 2021, The Trails of M-22: Clarkston, Michigan Trail Maps.

Hooker, T.S., 2014, The Last Ice Age and the Leelanau Peninsula: Indianapolis, Dogear Publishing.

Gowganda Tillite: Evidence for Early Proterozoic Continental Glaciation

 By Steven Wade Veatch

Gowganda tillite (figure 1) is lithified glacial till (sediment deposited by glacial ice) from a Precambrian glaciation event that occurred over two billion years ago. Glacial till was buried, and over time, it lithified or turned into rock (tillite). 

Figure 1. The Gowganda tillite is composed of sediment that was deposited by a glacier and later cemented to form a rock. Its pink clasts make it distinctive. Gowganda tillite is among the oldest rocks on Earth—about 2.3 billion years old. This specimen is from the outer limits of the city of Gaylord in Otsego County, Michigan. From the collection of S. W. Veatch. Photo by S. W. Veatch. 

Billions of years later, glaciers from the last Ice Age moved fragments of Gowganda tillite from their source location in Canada and dropped them onto the Michigan landscape as the climate warmed and the ice melted. Their pink clasts make them distinctive. This is only one of several Precambrian tillites found in the glacial drift of Michigan. The Gowganda and other tillite deposits in North America provide a rock record of the continental glaciation that occurred during the Early Proterozoic (Lindsey, 1969; Young and Nesbit, 1985, Crowell, 1999).

Geologists are now convinced that widespread glaciation occurred throughout the Early Proterozoic Era, based on at least 300 Precambrian sites, including Finland, South Africa, India, and Australia, that have tillite or deposits that resemble tillite (Wicander and Monroe, 2016). Five more major periods of widespread glaciation followed the Early Proterozoic (see table 1).

Table. 1. When Glaciers Covered Parts of the Earth (Crowell, 1999)
1	Late Cenozoic glaciation: began 33.9 million years ago at the Eocene-Oligocene Boundary and is ongoing
2	Late Paleozoic ice ages 338 to 256 million years ago
3	Late Devonian-Early Carboniferous ice ages, two short episodes between 353 to 363 million years ago
4	Ordovician-Silurian ice ages 429 million years ago to 445 million years ago
5	Late Proterozoic ice ages ~ 520 million years ago to 950 million years ago
6	Early Proterozoic ice ages ~ 2.2 to 2.4 billion years ago
7	Archean glaciation ~ 2.91 to 2.99 billion years ago

The source of Gowganda tillite is the Gowganda Formation which forms part of the Huronian Supergroup of Precambrian sedimentary rocks exposed in central Ontario, stretching from Lake Superior to Quebec (Lindsay, 1969; Elyes and Young, 1994). Radiometric dating places the age of the Huronian Supergroup from 2.1 to 2.5 billion years old (Van Schmus, 1965, p. 769).

Geologists have interpreted rock fragments in the Gowganda tillite to be the outwash associated with the Early Proterozoic Gowganda glaciers centered southwest of Hudson Bay. Melting ice rafts (calved from ice sheets) dropped these pink granite fragments—from tiny particles to boulder-sized debris—into open water. These pink pebbles fell through the water and settled into fine-grained sediments (Kurtz, 1980). Those sediments likely originated around a glacier's margins (Kesler, 2019). Over time, these sediments were lithified or turned to rock.

After these sediments were lithified, they were carried away, at least two billion years later, by Pleistocene glaciers. After the ice of these last Ice Age glaciers melted, the ancient conglomerates were released onto the landscape, later to be found on beaches and in farmers’ fields in Michigan. Scientists have also found Gowganda tillites in Wyoming and Quebec, Canada.

Gowganda tillite (figure 2) is a conglomerate composed of well-rounded to sub-angular, to angular, poorly sorted clasts (granitic and gneissic pebbles dominate) scattered in a tough, massive matrix of coarse to very fine sand and chloritic[1] material ( Kurtz 1980). Rounding suggests some history of water transport prior to incorporation into the tillite. 

Figure 2. A sawed section of Gowganda tillite shows dropstones of various sizes. Sorting is completely lacking in most Gowganda tillite. From the collection of S. W. Veatch Photo by S. W. Veatch.

 The Gowganda tillite is one of the most well-known ancient glaciogenic deposits in the world because of its characteristic pink, granite clasts (pebbles) held in a fine-grained gray matrix (Kesler, 2019). Today, the Gowganda tillite—among some of the oldest rocks on Earth—continues to be studied by geoscientists. Samples are also sought after by rock and mineral collectors for their unique combination of unsorted pink pebbles, age, and interesting formation.

References and further reading:

Crowell, J. C., 1999, Pre-Mesozoic ice ages: their bearing on understanding the climate system (Memoir 192). Geological Society of America.

Eyles, N. and G. M. Young, 1994, Geodynamic controls on glaciation in Earth history, in, The Earth’s Glacial Record, eds. M. Deynoux, et al, eds: Cambridge, Cambridge University Press, p. 1-28.

Kesler, S. E., 2019, Great Lakes Rocks: 4 Billion Years of Geologic History in the Great lakes Region: Ann Arbor, University of Michigan Press.

Kurtz, D. D., 1980, Stratigraphy and Genesis of Early Proterozoic Diamictites: North America: PhD Thesis, Huston, TX, Rice University.

Lindsey, D. A., 1969, Glacial sedimentology of the Precambrian Gowganda Formation, Ontario, Canada: Geol. Soc. America Bull., v. 80, p. 1685-1702.

Young, G. M., and H. W. Nesbitt, 1985, The Gowganda Formation in the southern part of the Huronian outcrop belt, Ontario, Canada: Stratigraphy, depositional environments and regional tectonic significance: Precambrian Research, v. 29, p. 265-301.

Van Schmus, R., 1965, The geochronology of the Blind River-Bruce Mines area, Ontario, Canada: Jour. Geology, v. 73, no. 5, p. 755-780.

Wicander, R. and J S. Monroe, 2016, Historical Geology: Evolution of Earth and Life Through Time: Boston, Cengage Learning.

 

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[1]Chlorite is a group of silicate clay minerals occurring in both macroscopic and clay particle sizes; they are hydrous aluminum silicates, usually of magnesium and iron. Chlorites have a silicate layer structure similar to that in micas. Source: Britannica.

The Michigan Puddingstone

Steven Wade Veatch

Michigan’s puddingstones are intriguing rocks that look like a glob of pudding stuffed with raisins, nuts and bits of cranberries. These white rocks, with small red, brown, purple and black pebbles, are not a Michigan product. During the last ice age, they hitched a ride into Michigan on an ice sheet and got off in the southern part of the state when the ice melted.

Fig. 1. An unpolished puddingstone from Michigan. Some contain trace amounts of gold and diamonds. These rocks are commonly found just after farmers plow their fields in Michigan.  Puddingstones were brought to Michigan by Ice Age glaciers. Jo Beckwith Specimen.  Photo by S.W. 

Puddingstones went through several steps in their formation (in what is now part of Ontario in Canada), before they went on their journey to Michigan. First, a network of rapidly flowing streams tumbled red and coffee-brown jasper, funeral-black chert, hematite and quartz in their churning water. Next, the streams deposited the material as sedimentary fill in eroded troughs and as alluvial fans, when the streams reduced their velocity and scattered the colorful pebbles onto mounds of sand (Lowey, 1985; Baumann et al. 2001). 

Then, the sand and pebbles hardened beneath the Earth’s surface and, over time, formed sedimentary rocks known as conglomerates (Slawson, 1933).  Later, intense heat and pressure metamorphosed the matrix of sand into a light-colored, coarse-grained, sugary-textured quartzite that tightly held the pebbles (Schaetzl, n.d.).  These geological forces formed the puddingstones around 2.3 billion years ago.

Today, geologists recognize these conglomerates as part of the Lorrain Quartzite of the Cobalt Series (Door and Eschman, 1970). This rock formation occurs as thick beds at Saint Joseph Island in Northern Ontario, Canada. The conglomerates also are found by the Saint Mary's River north of the Bruce Mines. This area is located 65 km (40 miles) east of Sault Sainte Marie in Ontario.

Puddingstones traveled south during the last ice age with the immense Laurentide Ice Sheet as it flowed at a glacial pace down from Canada. This ice plucked the puddingstones from the underlying bedrock, carried them hundreds of kilometers, and delivered those rocks to Michigan about 24,000 years ago.

  

This slowly advancing ice plowed across the landscape for thousands of years until rising temperatures, brought on by a climatic shift, ended their movement in Michigan. As the glacial ice melted, it deposited glacial till that contained the puddingstones. 

Today, farmers in the southern part of Michigan find puddingstones after spring plowing.  Since tightly cemented puddingstones can be cut and polished, they are in demand by Michigan artists and crafters, who make jewelry and ornaments out of them.  Puddingstones are commonly found as garden decorations that adorn Michigan homes and farms. People also collect and display puddingstones for their striking colors and appearance. 

Fig. 2. Since puddingstones are so hard, they take a nice polish as seen in this example. 
Steven Veatch specimen. Photo by S.W. Veatch.

In fact, as grandparents and parents take children outside to hunt for puddingstones, they pass an interest in puddingstones and geology down through generations of Michigan families. The tradition of looking for these goes back to the settlement of Michigan, and there is no sign of this interest ending anytime soon. 

References cited:

Baumann, S. D., J. T. Arrospide, and A. E. Wolosyzn, 2011, Preliminary Redefinition of the Cobalt Group (Huronian Supergroup), in the Southern Geologic Province, Ontario, Canada. Midwest Institute of Geosciences and Engineering, Chicago, Illinois, USA.

Door, J. A. and Eschman, D., 1970, Geology of Michigan: Ann Arbor, The University of Michigan Press.

Lowey, G.W., 1985, Stratigraphy and Sedimentology of the Lorrain Formation, Huronian Supergroup (Aphebian), Between Sault Ste. Marie and Elliot Lake, Ontario, and Implications for Stratiform Gold Mineralization, Open File Report no. 1154. Geological Survey of Canada, Ottawa, Canada.

Schaetzl, R. J. (n.d.), Geography of Michigan and the Great Lakes Region. Retrieved, from http://geo.msu.edu/extra/geogmich/Puddingstones.html on January 22, 2020.

Slawson, C. B., 1933, The Jasper Conglomerate, an Index of Drift Dispersion. The Journal of Geology, Vol. 41, No. 5, p. 546–52.