Stromatolites Lake Michigan Discovery

Lake Michigan Stromatolite Fossil (Same as sample below, wet to bring out layers)

Stromatolites Lake Michigan Beach Fossil






You’re strolling along the shoreline of Lake Michigan combing the beach for interesting stones and driftwood or perhaps beach glass. You find a gray beach stone commonly found. You admire it for the smooth way it feels in your hand, ground down by the wind, wave and sand action. It even smells of the fresh outdoors. But upon a closer look, you can see layers of striations interesting and beautiful. When wet, they suddenly pop out and there’s no mistaken this is not an ordinary mineral rock. It’s a stromatolite.

Lake Michigan Beach Stromatolite Fossil

Lake Michigan Beach Stromatolite (Same as fossil left wet)

What Are Stromatolites?

For us laymen, simply put, they’re fossils of bacteria. You need a firm understanding of biology, geology and chemistry to fully understand them. Nevertheless, I will attempt to delve into their fascinating formation.

Forming in water, scientists today generally agree stromatolites are layered structures formed by cyanobacteria, single-cell microorganisms capable of photosynthesis producing their own food. Cyanobacteria are prokaryotic cells (the simplest form of modern carbon-based life) in that they lack a DNA nucleus. Bacteria, including the photosynthetic cyanobacteria, were the only form of life on Earth for the first two billion years that life existed on Earth.

Forming The Layers

The stromatolite bacteria live in between thin sheets of filament bound together by a sticky substance. Photosynthesis in the bacteria depletes carbon dioxide in the surrounding water making it less acidic and initiating the release of calcium carbonate. Calcium carbonate and other minerals and grains of sediment settle, then get trapped on the outside sticky layer. The cyanobacteria thus rises to the top of the stromatolite structure over the sediment and the layers recycle repeatedly building the solid structures that can take several forms such as mounds, sheets or columns which appear like giant mushrooms.

While the microbes that construct the layered mats generally are not preserved, the wrinkled calcium carbonate, mineral rich layers remain in the fossilized forms.

Stromatolites are the oldest discovered fossils dating as far back as 3.5 billion years. First appearing during the Archean Eon, their hay day was during the Upper Proterozoic Eon long before multi cellular Cambrian creatures evolved.

Geologic time scale showing stromatolites being most abundant during the Late Proterozoic (Condie and Sloan, 1997)


The stromatolites forming today in the shallow waters of Shark Bay, Australia are built by colonies of microbes. Credit: University of Wisconsin-Madison

Modern stromatolites were first discovered growing in the salty waters of Shark Bay, Australia in 1956. Before then, scientists believed they were extinct. Other locations discovered around the globe include the shallow waters of Yellow Stone, Mexico, Canada, Brazil, Oregon and most uniquely, Bahamas. Stromatolites lost out when animals such as snails evolved that ate them. Modern stromatolites thus live in water too salty or hot for those predators, except in the Bahamas. Watch the video to find out why!

Studies of modern stromatolites have shone they are not uniform in shape and form, but also host a variety of bacteria and archaea (bacteria like microorganisms). Archaea usually live in extreme, often very hot or salty environments such as hydrothermal vents or mineral hot springs, ie Yellow Stone. In any event, various biological environmental conditions may attribute to the differences in their make-up and shapes. Some form a round ball or lumpy mass. The example below shows one of these such forms found on a Lake Michigan beach.

Lake Michigan Stromatolite Fossil

Some of the most ancient stromatolite fossils found are in the 3.35 billion year old Strelley Pool chert of Western Australia, part of a fossilized ocean reef. Seven different types were identified, so there was already a variety of stromatolite shapes even back then. The stromatolite fossils found in Michigan are typically younger, dating from 2.2 billion years ago. During the great ice age 10,000 years ago, glaciers cut the Great Lakes digging up time-buried layers of sediment containing many varieties of fossils we find on the beaches today. This could explain how I picked up the stromatolite fossil pictured above on the beach in Southwestern Michigan.


Lake Michigan Stromatolite Fossil

Lake Michigan Stromatolite Fossil (Same as sample on left, wet to bring out layers)








Why Are Stromatolites Important To All Life?

Cyanobacteria that make up stromatolites were ultimately responsible for one of the most important global changes that the Earth has undergone. Being photosynthetic, cyanobacteria produce oxygen as a by-product. Photosynthesis is the only major source of free oxygen gas in the atmosphere. As stromatolites became more common 2.5 billion years ago, they gradually changed the Earth’s atmosphere from a carbon dioxide-rich mixture to the present day oxygen-rich atmosphere. This major change paved the way for the next evolutionary step, the appearance of life based on the eukaryotic cell (cell with a nucleus).

Stromatolites in the Soeginina Beds near Kübassaare, Saaremaa, Estonia

Stromatolites at Highborne Cay, in the Exumas, The Bahamas


Mystery Fossils Found Wintertime Lake Michigan Beach


Winter 2010/2011

Most years, Lake Michigan’s wave action and chilling temperatures pushes ice and snow into huge mounds over the shoreline as high as twenty feet (shown above). In order to actually see the big lake you have to climb the mounds without falling in. Danger lurks around those edges where people can and have fallen through.

It’s January 2013 and the second consecutive season where the sand is left bare of winter’s icy layers; which I can’t stress enough how extremely rare that is. Looking towards the horizon over Lake Michigan, you would normally see a frozen tundra of stillness. Not this year. Compare the photo above taken winter 2010/2011 from the photo below taken winter 2012/2013.

Lake Michigan 2013

Lake Michigan Unfrozen January 2013

Case in point; due to the season’s whirling winds, minus the layers of snow, and less tourist traffic, fossils are more exposed from the continuous movement of sand. Below, are several interesting samples of fossils I found on Oval Beach, Saugatuck, MI (USA) winter 2012/2013. I haven’t been able to fully identify these species partly due to their smoothed surfaces, so please feel free to make suggestions. I have provided a few best guesses.

Coral Fossil, Geode or both?  Mystery Fossil 1

Coral with embedded crinoids

Crinoids embedded in coral or chunk of seafloor, Mystery Fossil 2

Fossil Coral

Sponge or Coral? Mystery Fossil 3

Fossil Coral

(reverse side of fossil above)

Favosite and Rugose Corals Named After Two Michigan Cities


Southwest Michigan Oval Beach old pier pilings and rocks reveal low water levels in 2012

During the month of December, the ground is usually  covered with layers of snow here in Southwestern Michigan (USA) and the big lake looks like a frozen tundra. Fossil exploring is usually put on hold until Spring, but 2012, so far, has shown to be a mild winter. As a result, the sand along the shores of Lake Michigan is more exposed to strong winds which has actually assisted fossil finding. The moving sands reveal hidden treasures one must partake while it lasts.

Below, are two recent discoveries of extinct corals found on Oval Beach located in Michigan’s southwestern tourist town of Saugatuck. Although closely related and most common during the Silurian and Devonian time periods, the two corals derive from different orders by virtue of their skeletal growth patterns (tabulate and rugose) respectfully. Colonial building favosites are the most common form belonging to the tabulate group while the individual horn corals are probably the most well known among the rugose group. But don’t be fooled, the rugose order also included some colonial varieties.

Follow below as I define some of the characteristics of each order and try to guess for yourself which orders these two fossils fall under. Answer at the end.

The “tabulae” from the order tabulate refers to the horizontal internal partitions visible from a side view of a good specimen. Observe the diagram below of a favosite fossil. 


Rugose corals (named for their wrinkly outer skin) had less developed horizontal partitions, but stronger vertical ones. Most rugose corals have septae radiating from the center (like bicycle spokes) when observed in a cross section.



Many tabulate corals can be associated with smaller honeycomb patterns of their corallite structures which housed the jelly-like polyp creatures. Whereas the rugose corals are often associated with larger more hexagonal patterns of their corallites.


Southwestern Michigan Oval Beach

The first Michigan fossil I found on Oval Beach in  southwestern Michigan is often referred to as the Petoskey Stone  “Hexagonaria, percarinata”  named after the northwestern city of  Petoskey, Michigan where they are commonly found. It’s  about the size of a fist and is rather smoothed out from water and sand action, yet it’s a nice large specimen that reveals the entire coral. From the side view, you can clearly see how it was attached to the seafloor by its stem.




Petoskey Stone


Side View of Petoskey Stone

Petoskey 2

Details of Petoskey Stone Corallites


Petoskey Stone, “Hexagonaria, percarinata” Rendering/Drawing


The other extinct Michigan coral fossil I found on Oval Beach is nicknamed the Charlevoix Stone. It’s smaller in total size, but is especially distinguished by its smaller honeycomb like corallite patterns.


Charlevoix Stone


Side view of Charlevoix Stone


Favosite Drawing Rendering  “Charlevoix Stone”

The two Michigan cities of Petoskey and Charlevoix lie in close proximity to each other in the NW region of the lower peninsula. Yet, both cousin fossils can be found on the far southern shores of Lake Michigan’s coastline where I found my fossils south of Grand Rapids seen on the map.


Petoskey and Charlevoix are far north of Saugatuck’s Oval Beach


Petoskey and Charlevoix in close vicinity










So, if you haven’t already guessed which order the Petoskey and Charlevoix Stones belong, here’s the answer. The Petoskey belongs to the order of rugose corals with its hexagonal patterns and the Charlevoix is from the order of tabulate corals with its honeycomb patterns.


Recent Find (Halysite Coral)

Golden Beach grass dune

Oval Beach Saugatuck, Michigan  Winter 2012


I was super excited to discover some fossils on Oval Beach in Saugatuck, Michigan (USA) that are highly unusual to find in winter. The sample below is an extinct tabulate coral, a reef building colony type coral called halysite. But we often find these saltwater varieties from the Paleozoic Era on our fresh water Lake Michigan shores. To explain this phenomenon I’ve written an article  entitled “I Found a Fossil on the Beach and Wondered” at where I’m also the Fossillady. A link is provided in the box to the right.

This halysite coral is easy to distinguish due to the chain link appearance coining it with the common name “chain coral”. It was lying under layers of sand that aren’t usually exposed during the winter months. But the mild weather with little snow has allowed winter winds to push sand off the under layers. It’s also due to low water levels from a long dry spell during summer 2012, there’s more beach to explore.

The extinct halysite corals displayed small tubes from which resided the jelly-like coral animals called polyps.  The coral polyps contained stinging cells for protection and also grasped plankton food that passed by in the ocean currents. As the halysite corals grew, they built up walls of tube-like chambers called theca which steadily multiplied adding more links to the chain. In their hay-day as they continued to multiply, they built large limestone reef structures on the seabed. They thrived mostly during the Silurian period up to 425 million years ago!


Kingdom: Animal

Phylum: Cnidaria (means stinging animal)

Class: Anthozoa (means flower animal)

Order:  Tabulata (possess inner horizontal dividing walls from growth patterns)

Family: Halisitidae (means chain coral)

Genus: Halysite  Species:unknown

Halysite Coral

Halysite Coral Fossil


Halysite Colony “Chain Coral” Rendering