Geological History of Jamestown, Rhode Island

Building New England:
The Taconic and Acadian Orogenies

The land that became New England was added to the core of North America between about 465 to 400 million years ago as two island arcs collided with the growing land mass.

These two island arcs, the Taconic and Avalonian, which had been moving northward from their places of formation near the juncture of South America and Africa, impacted with Laurentia (Proto-North America). These long island chains also added land to what is now eastern Canada, to what is now Greenland, and to other parts of the current eastern U.S. states, as far south as the Carolinas.

Orogeny is a geological term for the process of mountain-building. Orogenies are driven by collision of land masses.

 
The two drawings above, one schematic and one pictorial, provide an overview of the process which added most of what is now New England to the eastern coast of Proto North America about 430 million years ago, They are adapted from a set of paleographic views of Earth history by Dr. Ron Blakely, Northern Arizona University. The series of collisions added land from eastern Canada to the Carolinas.

At the time, Greenland was nestled against northern Canada. Part of Siberia is visible at upper right (in the drawing on the right). At that time, Proto North America was straddling the equator.  The present "east coast" was, at that time, essentially a "south coast". Much of the US and Canada was covered by shallow seas. Baltica, the core of western Europe, which had been moving westward, has made impact against Greenland. Mountains were being raised on both of those continents.

The Taconic island chain (TAC) began to collide with Proto North America about 40 million years earlier than the Avalonian arc (470 to 450 million years ago). The energy of the ongoing impacts was still raising mountains from Canada to Virginia 430 million years ago.

The Iapetus Ocean, which had been the shoreline for Proto North America, was closing as Western and Eastern Avalonia (WAV and EAV), following behind the Taconic arc, are heading for collision with the recently-extended coast of Proto North America. A wide swath of Iapetus Ocean seabed material will be pushed onto Proto North America as the Avalonian islands push against and onto Proto North America.

The Taconic Orogeny - Circa 450 Million Years Ago

Prior to the Taconic orogeny, the "east" coast of what is now the United States was located near the Hudson River valley, Philadelphia, Washington, DC and extended to western South Carolina. The Taconic Orogeny added land to Proto North America that is now the western portions of New England and the Canadian Maritime provinces. This collision added land and raised mountains southward through northern New Jersey, south-eastern Pennsylvania, Virginia and North Carolina. The orogeny ended about 445 million years ago.

The first set of pictures show the world between 500 and 460 million years ago. Note the movement of an arc of small islands (the Taconic Arc, located just above the symbol T__T in the right hand panel) as they moved northward, away from the South American coast (near present-day Colombia) toward Proto North America. The Taconic island arc bumped into Laurentia starting about 470 million years ago.

The first impact was against what is now Greenland and eastern Canada. Moving southward, the collision zone moved through New York, near the present Hudson River valley. The Taconic mountain chain was created as the arc rode up and onto the Laurentian land mass, a part of which was subducted (drawn under) the Taconic arc. (Outside of New York state these mountains may have many different names, and are often heavily eroded).

The oval drawings were derived from an animation sequence by Christopher R. Scotese and the Paleomap Project. J indictates the approximate location of present-day Jamestown. The close-up artist renderings on this page are derived from a series by Dr. Ron Blakely, Professor of Geology, Northern Arizona University.


Avalonia Collides with Proto North America
The Acadian Orogeny - Circa 400 Million Years Ago

In the sequence of drawings below, you can see that, about 460 million years ago, the eastern end of the Avalonian arc was approaching Baltica (Proto Western Europe). Around 440 million years ago, these two land masses had "docked".

The Acadian Orogeny started about 430 to 425 million years ago, when the Avalonian arc, moving northwest, and Baltica, moving west, impacted against the southward-moving Proto-North America.

The eastern (northern) portion of Avalonia was sandwiched between both eastern Canada and parts of Baltica. Contact between Avalonia and Proto North America progessed to the south and west over the next 40 million years.

Ongoing collisions created the Northern Appalachian mountains. The event is known as the Acadian orogeny (or sometimes the Appalachian or Avalonian orogeny)


As Avalonia advanced, the basaltic bed of the Iapetus Ocean was pulled under Laurentia (subducted) and melted. Volcanos formed in and near the narrowing ocean. The Northern Appalachians rose as the land was compressed and bent.


Large volumes of volcanic material and Iapetus Ocean sediments were pushed onto the margin of Laurentia as the land masses converged, forming a band of younger terrane between the older Laurentian and Avalonian terranes. This now-metamorhosized material is found in the present states of Maine, New Hampshire and Vermont plus major parts of Massachusetts and Connecticut.

In this sketch of the New England states, Iapetus Terrane is colored light grey. It typically contains schist, phyllite, gneiss and granite. Avalon Terrane is shown in dark grey. All of Rhode Island's foundation rocks were part of Avalonia itself. "Avalon terrane" is also found in eastern Maine, Massachusetts and Connecticut.

South Carolina also contains Avalonian Arc material (sometimes called Carolina Terrane). It is also found in New Brunswick, Newfoundland and Nova Scotia; as well as Morocco, Portugal, Spain, Ireland, Wales, southern England and the northern coasts of France, Belgium, Holland and Germany.

 

By about 360 million years ago the Northern Appalachian mountains had become greatly eroded.

During this period, life was beginning to move onto land as well as sea. Vascular plants appeared that could grow tall. Ferns, reeds and horsetails evolved. Insects and amphibians appeared. Tall conifer trees developed and forests appeared.


Continue with the next installment of this narrative

Alleghenian Orogeny

North America collides with Africa, pushing the Appalachians higher,
forming the supercontinent Pangaea, and creating the Narragansett Basin

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

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