Stromatolites Lake Michigan Discovery

Lake Michigan Stromatolite Fossil (Same as sample below, wetted 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 common gray beach stone and admire it for the smooth way it feels in your hand, ground down by the wind, wave and sand action of the big lake. 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.



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.

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

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)


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.

Stromatolites in the Soeginina Beds (Paadla Formation, Ludlow,
Silurian) near Kübassaare, Saaremaa, Estonia

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, red in color from iron infused sediment.

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

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 at Highborne Cay, in the Exumas, The Bahamas

All rights reserved © Fossillady 2011


Halysites Chain Coral Uncovered

Golden Beach grass dune
Oval Beach Saugatuck, Michigan  (Winter 2012)

I was super excited to discover several fossils on Oval Beach in Saugatuck, Michigan, USA that are highly unusual to find in winter. The fossil below was lying under deep layers of sand, but luckily, the mild weather with minimal snowfall allowed winter winds to push sand off the under layers. Also contributing to fossil hunting were the low water levels from a long dry spell during summer 2012, which produced more beach to explore.

Halysite Coral
Halysites Chain Coral Fossil Found on Lake Michigan Beach

These fossil samples are extinct tabulate corals, reef building colony-type corals, Halysites, commonly called, Chain Corals. They are fairly easy to distinguish due to the chain-link raised marks for which they’re named.

Halysites Chain Coral Fossil Found on Lake Michigan Beach

In life, the extinct Halysites corals possessed small tubes where the jelly-like polyps resided. The coral polyps contained stinging cells for protection and also for siphoning plankton and organic matter passing by in the ocean currents. As the Chain Corals grew, they built up walls of tube-like chambers called theca which steadily multiplied while adding more links to the chain. In their heyday, they built large limestone reef structures on the seabed. They thrived especially during the Silurian period as far back as 425 million-years-ago!

Halysites Chain Coral Classification

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: Halysites  Species: unknown

Halysites Chain Coral Rendering Showing Polyps Extended

Explore more Lake Michigan fossils in another photo-essay I provided, otherwise, keep scrolling!

All rights reserved © Fossillady 2011