Discover Canada and Explore the Fossils and Geodiversity of Anticosti Island in Québec
- Wayne Munday
- Oct 1
- 5 min read
Sip back and discover Canada and explore the fossils and geodiversity of Anticosti Island at the mouth of the St. Lawrence in Québec. This globally significant destination was recognised by UNESCO as a World Heritage Site in 2023 for its exceptional fossil record of the Late Ordovician Mass Extinction (LOME) and Early Silurian marine recovery between 447 - 437 million years ago. Stretching for over 222 Km's, Anticosti Island exposes a near continuous succession of carbonate rocks laid down in a warm shallow sea and include the Ellis Bay, Vauréal, Gun River, Jupiter and Becscie Formations preserving nearly ten million years of marine life. The Late Ordovician Ellis Bay Formation records storm-influenced carbonate-siliciclastic deposits with diverse fossils including brachiopod such as Hirnantia notiskuani whilst the Vauréal Formation preserves soft-bodied organisms. The Early Silurian formations of Gun River, Jupiter and Becscie tell a story of biodiversity recovery, reef development and ecological stabilisation. Anticosti’s thick, largely undeformed rock and tempestite or storm-generated sedimentary layers holds is where three-dimensional fossils are preserved.
Anticosti Island lays at the mouth of the St. Lawrence in Québec’s Côte-Nord. At about 222 Km long and up to 56 Km wide the only remaining village on the island is Port-Menier. These lands lie within the territories of the First Nations Innu communities of Ekuanitshit and Nutashkuan. In September 2023, UNESCO recognised the island as a World Heritage Site acknowledging its unparalleled geodiversity associated with the Late Ordovician Mass Extinction (LOME) and the subsequent recovery of Early Silurian marine ecosystems.
The Anticosti Island has five significant shallow-marine formations that span from the Upper Ordovician through to the Lower Silurian including the Ellis Bay, Vauréal, Gun River, Jupiter, and Becscie formations that each capture a distinct episode of environmental change, biodiversity loss and post-extinction recovery. Anticosti is an example of a gently sloping shallow shoreline that accumulated carbonate muds, shell beds and small reef patches under tropical and shallow-marine conditions. Repeated storm events generated tempestite beds that rapidly buried benthic communities preserving fossils in life position and conserving delicate shell microstructures.
The Ellis Bay Formation which dates to the Upper Ordovician Hirnantian stage between 445.2 - 443.8 million years ago and is a mixed carbonate reefal succession extending along a 200 Km east-west coastal belt shaped by storms and preserves benthic or seafloor communities in their life position. Fossil assemblages are abundant and diverse including ostracods, crinoids, corals, brachiopods especially Hirnantia notiskuani and trilobites such as Acernaspis, Celtencrinurus, Isotelus and Mucronaspis whose appearance and disappearance indicate biodiversity loss at the Ordovician – Silurian boundary.
Interestingly within the Ellis Bay Formation are diploporitan fauna an extinct Holocystite echinoderm a relative to crinoids. There disappearance coincides with climate change linked to the short but intense episode of global cooling known as Hirnantian glaciation that triggered a global mass extinction event. Vast ice sheets spread across Gondwana driving a dramatic fall in sea level that exposed shallow seas and wiped out habitats vital to trilobites, corals and brachiopods. Lasting only about 1.4 to 2.1 million years this glaciation marked the first major extinction of the Phanerozoic.
Overlying the Ellis Bay Formation is the Vauréal Formation dating to the Katian Age the second of three ages within the Late Ordovician Epoch spanning from approximately 452.8 to 445.2 million years ago. Layers of limestone and marlstone were deposited in a shallow tropical sea over 7.6 million years and holds some exceptionally well preserved of soft-bodied organisms. Fossils from this formation include delicate soft-bodied animals including Acoelomorpha, Turbellaria, Nemertea, and Nematoda that are often preserved as pyritic aggregates or sediment-filled voids, alongside microfossils like chitinozoans and calcareous algae.
A) Cluster of the athyridide Koigia on bedding plane; B) Shell bed composed largely of the monospecific atrypide Becscia , locally common in localities from Natiscotek to Fox Point area; C) Abundant gastropods locally cover bedding plane surfaces in the eastern facies; D) Leptaena -rich shell bed, especially abundant in the eastern facies from Salmon River to the Jupiter River; E) Mendacella shell bed with abundant match-stick bryozoans; F) Bryozoan Phaeonopora superba; (G–K) Dorsal, ventral, lateral, posterior and anterior views of Zygospiraella cf. and Z. planoconvexa
Transitioning into the Early Silurian and into the Rhuddanian Age between 443.8 - 440.8 million years ago and the first stage of the Llandovery Epoch. Following the Late Ordovician mass extinction that saw the demise of about 85% of species this was a time marked by severely oxygen poor or anoxic seas, low biodiversity and a slow recovery of marine ecosystems. The Gun River Formation captures the start of post-extinction marine recovery in its 85 –100 meter-thick carbonate succession. The fossil record is expectedly low in diversity and is dominated by a small number of brachiopods especially the large pentamerids such as Pentamerus and corals.
The Jupiter Formation spans both the Aeronian to Telychian stages between 440.8 - 433.4 million years ago. The Jupiter Formation is made up of six members called Goeland, East Point, Richardson, Cybèle, Ferrum and Pavilion and they tell a story of different environmental conditions, biodiversification and ecological rebound of tropical marine communities following the Ordovician mass extinction.
Fossil assemblages in the Jupiter Formation are rich and diverse with invertebrates including brachiopods, trilobites, corals, and conodonts and its their exceptional preservation that underwrites Anticosti Island’s UNESCO World Heritage designation. The Jupiter Formation has an abundance brachiopods such as Striispirifer, Eospirifer, Gotatrypa, Pentamerus, Eocoelia, Pentameroides, and Costistricklandia, alongside solitary and colonial corals like favositids, heliolitids, and rugosans. Stromatoporoids are particularly well developed in the Pavillon Member where they contributed to the formation of early coral–sponge patch reefs, while crinoid remains are especially common in the upper Ferrum Member and provide the foundation for reefal ecosystems.
Capping the Early Silurian sequence is the thick Becscie Formation comprising of two members called the Fox Point Member at the base, corresponding to the Viridita lenticularis Biozone, and the Chabot Member above, encompassing the Virgiana barrandei Biozone. The Becscie Formation on Anticosti Island captures the re-establishment of benthic ecosystems and recovery of a shallow marine ecosystems following the Late Ordovician mass extinction.
Anticosti Island is a remarkable destination where geology, wilderness, and adventure converge. The island’s dramatic scenery of fossil-rich limestone cliffs, deep canyons, vast forests and vast cave systems making it an opportunity to experience pristine natural Canadian wilderness to explore in solitude. Wildlife thrives here, with an abundant deer population, rare species like the Anticosti warbler, and marine life ranging from seals to whales. Outdoor adventurers can also enjoy over 125Km of hiking trails and Atlantic salmon fishing in rivers like the Jupiter.
