South Michigan EarthCaches 


Blue Ridge Gravel Pit EarthCache Part 3 – Fossiles 

Connection to the Earth Science Curriculum

Essential Lessons:

The Blue Ridge Gravel Pit provides an opportunity for visitors to discover two interesting stories that involve orange-brown boulders or fragments of sandstone found that tell of times when the climatic conditions were vastly different in Michigan than they are today.

Earth Science Literacy Principles

  • Big Idea 2.1. Earth's rocks and other materials provide a record of its history.
  • Big Idea 2.7. Over Earth's vast history, both gradual and catastrophic processes have produced enormous changes.

Common misconceptions

  • Glaciers are ice and snow deposits on the land were no more than 50 feet thick.
  • Glaciers most recently covered Michigan millions of years ago.

Key Earth Science/Geological Vocabulary Words:

Cementation: The process of binding sediments or grains together to make sedimentary rocks.

Esker: A long winding ridge of gravel, sand, etc., originally deposited by a meltwater stream running under a glacier.

Glacial Till: Unconsolidated, heterogeneous mixture of clay, sand, pebbles, cobbles, and boulders deposited onto the landscape by retreating glaciers.

Laurentide Ice Sheet: A massive sheet of ice sheet that covered most of Canada and a large portion of the northern United States between 95,000 and 20,000 years ago.

Pleistocene Epoch: A small unit of time within the Cenozoic Era that encompasses the most recent glacial advances on our planet between 11,700 and 2.58 million years ago.

Wisconsinan Advance: The most recent period of continental glaciation in the northern hemisphere that occurred between 10,000 to 70,000 years ago. The height of the Wisconsinan Advance occurred nearly 20,000 years ago when glaciers made their furthest advance toward the equator.

Developed by: Mark Reed

The Blue Ridge Gravel Pit is owned by the Jackson Country Road Commission and provides an opportunity for approved visitors (Permission must be obtained, see access information below) to discover two interesting stories that can be told that involve orange-brown sandstone boulders or fragments found within it. These boulders tell a story of when climatic conditions were vastly different than what they are today in Michigan.

Coordinate: N 42° 09.655′ W84° 21.318′

The Blue Ridge Gravel Pit has an additional story to tell beyond its glacial roots. The main storyline of this EarthCache exercise examines the orange-brown sandstone boulders and their plate-like fragments (Figure 1) that are easily found along the floor or at the base of any slope within the Blue Ridge Gravel Pit.

Figure 1: Orange-brown sandstone boulders and fragments of the Marshall Formation.
Photograph by Mark S. Reed.


At least two stories can be read from the orange-brown sandstone boulders of the Blue Ridge Esker. The first tells about the environmental conditions and fauna of the Mississippian Period and a time when Michigan lay near the equator (Figures 2). During this period of time, Michigan was covered with a vast shallow inland sea in the Michigan Basin (Figure 3).

Figure 2: Earth during the Mississippian Period.
Copyright by Christoper R. Scotese.


Among the animals present in this Mississippian Sea were cartilaginous fish or sharks, nautiloid and semi-coiled cephalopods and ammonites. In addition, pelecypods (clams) gastropods (snails), crinoids (sea lilies), trilobites, brachiopods, and a variety of types of corals were abundant (Figures 4 and 5).

Figure 3: North America during the Mississippian Period.
Please note that Michigan was covered with a shallow, warm sea that was rich with marine life.
Copyright by Ron Blakey of Colorado Plateau Geosystems, Inc.


Geologists often use fossils to establish the age of a rock formation. Fossils used for age-dating are known as Index Fossils. Cephalopods and ammonites make excellent index fossils because many have unique physical characteristics, lived over a short geologic time, and had a large geographical distribution since they were sea-dwellers. Secondly, when cephalopods and ammonites die, their remains have enough buoyancy that they can be carried by waves and currents to other locations where they can wash up onto a beach and/or be buried in the sand. Cephalopods and ammonites are sometimes found whole or broken depending on the energy of the beach environment.

Despite the fact that fossils can easily be found in many sedimentary rocks, the process of fossilization is relatively rare. In general terms, fossilization is limited to animals or plants with hard parts that have been buried quickly or have died in environments without abundant oxygen. Most animals and plants are not fossilized due to soft tissue, scavengers, and their remains being exposed to the elements. Exceptions to these rules are sometimes found in nature. Fossilization of soft tissue, whole-animal preservation, and delicate structures are extremely rare and usually involve encapsulation or burial in very fine sediments or substance in a low-energy or atypical environments.

Figure 4: Cartilaginous fish and crinoids of the Mississippian.


If a time-traveler was able to transport himself back to the Mississippian Period, he would probably enjoy walking along the sandy beaches of the Michigan Basin where he could dip his toes in the warm salty-surf. Here, he might see whole shells and fragments that tumble about in the waves as they lap up onto the beach. Stepping out of the surf, shell fragments might litter the beach that had previously been washed up during high tide. Others could be located by digging deeper into the sand that had been buried whole.

Figure 5: Life at the bottom of a Paleozoic coral reef


A trip back in time to the Mississippian of Michigan might invoke thoughts of visiting a warm tropical beach in the Bahamas. The beach and environmental conditions would be similar in many ways, and yet very different in terms of some of the animal fauna and the influence of man. However, if our time traveler could fast-forward to the present, he would discover that the sandy beaches and shallow marine environments would have lithified to form a layer of rock that is known by geologists as the Marshall Sandstone. Fossils associated with shelly life-forms provide Paleontologists an opportunity to examine the types of life present during the Mississippian Period and reconstruct their habitat.

A popular misconception that people have with fossils found in Michigan is that they were from a time when dinosaurs ruled the Earth. The fossilized life-forms found in the Marshall Sandstone lived at least 100 million years before the very first dinosaurs and nearly 265 million years prior to when the last dinosaurs became extinct.

Figure 6: A common ammonite of the Marshall sandstone. – Merocanites houghtoni.
Photograph by Mark S. Reed


Fossils from the Marshall Sandstone and the Blue Ridge Esker can be identified by using classic resources such as Geology of Michigan by John Dorr and Donald Eschman and the published papers by A.K. Miller and H.F. Garner. Both sources are useful because glacial deposits often contain fossils from several geologic time periods. Miller and Garner's works are more specific since they studied cephalopods and ammonites of the Lower Mississippian Period in Michigan like the fossil shown in Figure 6 of Merocanites houghtoni, a common ammonite found in the Marshall Sandstone.

Logging Activity/Question 1:

Locate several pieces of the orange-brown pieces of the Marshall that are rich with fossils. Sketch or photograph an example of a 1) Nautiloid Cephalopod 2) Pelecypod 3) Ammonite and 4) Crinoid. Please include a scale or measurement with any drawing or photograph.

What of the fossils collected above are preserved the best? Why do you think some types of fossils were preserved whole while others are almost always broken?


BONUS QUESTION

It was also during the Mississippian that ancient glaciers were developing in southern Gondwanaland causing sea levels to fall around the world. Falling sea levels also affected the Michigan Basin by causing the shoreline to shrink as water evaporated from the basin. Since the deepest part of the basin was near the middle of what is present day Michigan, the shoreline moved toward the middle of the state in ever-shrinking concentric rings during the remainder of the Paleozoic.

Figure 7: Bedrock map and cross-section of the Michigan Basin.


Not much is known about the Michigan Basin after the Paleozoic because the rock record is largely missing. Glaciers and other weathering events have erased the geologic rock record from the time of the dinosaurs and the rise of the mammals. What scientists do know about life and the events on our planet come from reading the rocks that have been examined from other locations around the world.

We find proof for a shrinking Michigan Basin by examining the bedrock that has been exposed in different locations from around the state and by drill cuttings collected by companies exploring for oil. Over the years, a picture of the Michigan Basin has emerged that shows what our state would like if we could remove the sand, soil, and gravel that was deposited onto the landscape during the Pleistocene Epoch by retreating glaciers. A quick examination of the Figure 7 shows concentric rings of bedrock that are youngest in the middle of our state in terms of geologic time.

Figure 8: Laurentide Ice Sheet and associated ice lobes


A basin structure is also confirmed by creating a profile plotting formation depth versus the distance between two points on a map like the black line that connecting points A and B on the map. Please note the light green color in Figure 7 represents the Marshall Sandstone of the Lower Mississippian. Bedrock formations toward the center of our state are progressively younger and are found closer to the surface.

The second story at this site looks at the journey that these orange-brown Mississippian-age boulders have taken during the Pleistocene Epoch when Michigan was covered by a vast continental glacier.

Figure 9: Ice Plucking of the local bedrock


During the most recent period of glaciation in Michigan, the Laurentide Ice Sheet (Figures 8) of the Wisconsinan Advance consisted of several ice lobes that flowed southward. As the mass and height of the ice sheet grew, ice at the bottom of a glacier becomes somewhat “plastic” and is able to pluck chunks of bedrock from the Earth and incorporated them into ice (Figure 9). Chunks of rock embedded into the ice scoured the bedrock as the glacier moved southward into Indiana, Illinois, and Ohio. Scientists estimate that some lobes may have been a few thousand feet thick. Some have stated that some portions were over a mile thick lobes may have been 10,000 feet thick.

As the glaciers retreated (Figure 11) 4,000 to 14,000 years ago, vast amounts of glacial till and outwash were deposited onto the landscape. Some of these sediments make up the Blue Ridge Esker, kettle lakes and ponds, glacial till and the outwash plains that can be seen today within Jackson County, Michigan.

Figure 10: Glacial retreat 4,000 to 14,000 years ago


Using your knowledge of the Blue Ridge Esker, maps of glacial lobes, bedrock maps, and the relative direction of both ice and water flow, indicate by drawing a narrow rectangle onto a printed copy of the bedrock map of Michigan's lower peninsula that is shown in Figure 11 where you think the orange-brown sandstone boulders most likely came from prior to being plucked from the bedrock and were later deposited at the Blue Ridge Gravel Pit.

BONUS Logging Activity/Question:

Using your knowledge of the Blue Ridge Esker, maps of glacial lobes, bedrock maps, and the relative direction of both ice and water flow, indicate by drawing a narrow rectangle onto a printed copy of the bedrock map of Michigan’s lower peninsula that is shown in Figure 11 where you think the orange-brown sandstone boulders most likely came from prior to being plucked from the bedrock and were later deposited at the Blue Ridge Gravel Pit?

What is the likelihood that a person might find fossils of animals from the Silurian or Devonian Periods in the Blue Ridge Gravel Pit? How could this be explained?


Figure 11: Using this modified bedrock map from the michigan department of natural resources, draw a rectangle that shows where you think the orange-brown boulders came from prior to being deposited in the blue ridge gravel pit.


Closing Comments:

At least two stories of climatic change can be told by reading the content held within the fossiliferous orange-brown sandstone boulders and fragments that are easily found at the Blue-Ridge Gravel Pit. These stories and others can be read by investigating other EarthCache sites that have been designed to help visitors discover the Big Ideas of Earth Science that explain the natural processes that act upon our planet.

Safety and Courtesy Note:

Since the Blue Ridge Gravel Pit is owned by the Jackson Country Road Commission, permission must be first obtained to enter. Visitors need to be vigilant in regard to safety and not attempt to climb steep slopes, get too close to cemented overhangs and structures, or climb up sand piles or slopes that could potentially collapse.