Geological History of Jamestown, Rhode Island


The area now known as Jamestown formed more than 565 million years ago, as part of a microcontinent called Avalonia (labeled the Avalonian volcanic arc in this sketch of the southern hemisphere).

The Avalonian arc formed as a volcanic archipelago off of both Africa and South America, at a time when they were joined together as part of Gondwana, part of which is shown in this sketch.

At that time, most of the world's land masses were south of the equator. The area that is now the Sahara Desert was located over the south pole !

Gondwana evolved after the breakup of Rodinia, an earlier supercontinent. Other major continents, then located in the northern hemisphere, were Siberia and North China.

Experts debate whether Laurentia was in contact with South America at this time. Those who believe they were, call the larger continent Pannotia. In any case, about 540 million years ago both Laurentia (proto North America) and Baltica (proto Western Europe) drifted away from Gondwana.

Rhode Island and the New England states were not the only land masses to emerge from the Avalonian arc. In the sketch above, J marks the approximate location of Jamestown. EW indicates the portion of Avalonia that became southern Ireland, England and Wales, Ib shows Iberia (Spain and Portugal) and Ar Armorica and Bohemia. A portion of the arc is now part of Morocco. Future parts of Nova Scotia, New Brunswick and Newfoundland, as well as most of New England are offshore from Florida (labeled F on the map). The portion of the arc that became part of the Carolinas is to the right of Jamestown, offshore of what is now Venezuela, in South America.

Follow this link to find an interesting account of unusual 565 million year old fossils found on Avalon Penninsula in Newfoundland, and their relataionship to fossils found in Charnwood Forest in central England. These fossils represent some of the earliest soft-bodied, multi-cellular organisms.

About the same time that Laurentia and Baltica moved away from Gondwana, the oxygen content of air stabilized at close to the current concentration.

Oceanic life forms began to explode in complexity and diversity starting around 545 million years ago. This “Cambrian Explosion” resulted in a huge variety of invertebrates including worms, clams, arthropods, corals and sponges.

Laurentia Moves Away from Gondwana

500 mya: The Avalonian Arc grows while Laurentia, Siberia and Baltica move away from Gondwana

Avalonia Moves Toward North America

Starting about 500 million years ago, Avalonia drifted north and west, away from Africa and toward Laurentia (Proto North America). Most of Laurentia was covered by shallow tropical seas in which were found rapidly evolving species of trilobites and echinoderms. Laurentia included not only the central portion of the present United States, but much of Canada, Mexico and Greenland.

Movements of the various land masses are depicted below. The drawings are derived from Paleomap Project views. (Plate tectonic maps and continental drift animations by C. R. Scotese, The PALEOMAP Project site contains a huge amount of data and offers free educational services. The pdf version of the main PALEOMAP site page is for quick reference.  See  ( for the most up to date links and services.

J marks the approximate location of Jamestown on these drawings. The full world views, commentary and related links can be accessed through the caption links.

As Avalonia journeyed across the Iapetus Ocean, life around it was evolving. Jawless fishes, coelenterates, arthropods, cephalopods, jawed fishes and coral reefs appeared.

About 435 million years ago, Avalonia docked with Baltica. Both were moving north and west, on collision courses with Laurentia.

Click this link to the next installment of this narrative

Building New England
The Taconic and Acadian Orogenies

About 450 million years ago an arc of small islands collided with Proto North America, adding a strip of land east of the Hudson River Valley.
About 425 million years ago, Avalonia collided with Proto North America, raising the Northern Appalachians and adding the remainder of New England.

Or, go directly to any Geological History page:

Introduction and Summary: 565 Million Years of Jamestown's Geological History
Prelude: The Earth's first 4 billion years - forming Proto North America, Rodinia, Gondwana
Avalonia: Rhode Island was once part of a micro-continent called Avalonia
Acadian Orogeny: Avalonia collides with the mainland of Proto North America (Laurentia)
Alleghenian Orogeny: North America collides with Africa, forming Pangaea
The Atlantic Forms: Pangaea breaks up, the Atlantic forms, the Appalachians erode
Glaciation: Glaciers form and rework the land
The Holocene Epoch: Post-glacial Rhode Island - rising seas - the time of modern man
Building the Northern Appalachians: Significant event summaries with links to more information
Guide to Bedrock in and around Jamestown and Narragansett Bay
Additional Information and References

Jamestown RI - Rhode Island Visitor Information Home Page

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