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Narraganset
Bay offers many reminders that it was
carved by glacial ice
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The story of
the land that is now Jamestown Rhode Island
Long ago - about 565
million years ago, and far away - near
the South Pole - approximately where the
coastline of Antarctica is located today - the
basement rocks beneath Jamestown (and all of
Rhode Island) were formed as part of a
volcanic arc called Avalonia.
The world was very
different then, in many ways. Land masses were arranged
quite differently than they are now. (Over time continents move,
at a very slow rate, roughly the rate at which finger nails
grow; but over millions of years, huge rearrangements occur; and
these will be traced in this narrative.)
The Avalonian arc formed offshore
of present day Morocco (northwest Africa) and
Venezuela (northern South America) when Africa
and South America were joined in a larger
continent which we call Gondwana.
To illustrate how much
the world has chanced since then, at that time, what is now the Sahara Desert, was
located at the south pole! |
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Rhode Island's nearest neighbor
(across-the-sea, as opposed to other parts of the
Avalonian volcanic arc) was located to the south,
closer to Gondwana, in a triangular bit of ocean.
It was an island - now known to us as the state of Florida.
To the west, along the arc, were parts of what
is now the eastern United States southward to the Carolinas. To the east were parts of present-day
Massachusetts, Maine, Nova Scotia, New Brunswick,
Newfoundland, Morocco, southern Ireland, southern
England, Wales, Portugal, western Spain,
northwest France, Belgium, Holland and northern
Germany.
There was no life on the land. Living things were found only in the sea,
and they were just beginning to evolve from
single-cell organisms into some of the
earliest soft-bodied, multi-cellular organisms.
To provide some sense of what
came before Avalonia formed, we have included a Prelude
that provides information on the first 4 billion
(4,000 million) years of continental formation
and evolution..
The main narrative traces
the journey of Jamestown's land across oceans and
through continental collisions to the relatively
recent past, when Rhode Island and surrounding
areas were sculpted by glacial action and
Narragansett Bay was created by the rising sea as the glacial
ice melted.
As you will see, quite literally,
Jamestown's land has been at the leading edge of
much of the world's history.
565 Million Years of RI Geological
History, and More
A Very Brief
Introduction and Summary
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of Rhode Island was part of a volcanic
arc or micro-continent called Avalonia, which formed south of
the equator more than 565 million years
ago, off of the coasts of both
Africa and South America, when they were
joined as part of a larger continent. At
that time, the Earth was about 4 billion
years old and living things were just
starting to evolve from single-cell
organisms into some of the
earliest soft-bodied, multi-cellular
organisms. Avalonia
drifted northward, away from Africa,
over the next 100 million years.
The
Avalonian arc collided with Proto North
America about 400 million years ago. The
impact contributed most of the land that
has become the New England states and
created most of the northern Appalachians,
as we know them.
The Appalachians are
actually a complex mix of mountains
formed by a series of continental
collisions, beginning with the (now
heavily eroded and often buried)
Grenville mountains (formed more than 1
billion years ago), the Taconic mountains (formed by another
island chain collision about 50 million
years prior to the collision with
Avalonia) and newer mountains formed
about 350 million years ago when North
America and North Africa collided, raising
portions to great heights. This collision
was one of several that formed a
supercontinent, Pangaea about 306
million years ago.
For more than
100 million years most of the world's
land was united. Jamestown was located thousands
of miles from the ocean, deep within that huge
supercontinent. This was the
time when dinosaurs appeared. The layers
of shale and coal that are common in the
Narraganset Bay area were formed during
this period.
About
200
million years ago, Pangaea broke up.
The Atlantic Ocean
formed and slowly widened.
As the Appalachians
eroded, land on both sides of
the mountain chain was covered with
sediment. To the east and south, the layers
of sediment formed the coastal plain
and the (now underwater) continental
shelf.
During the past 75,000
years, Jamestown was visited by
glaciers at least twice. They
gouged out channels in the Narragansett
Basin and left deposits of rocks and soil
throughout the area.
The last
glaciers left the area about 12,000 years
ago.
At that time,
sea level was hundreds of feet lower than
today. As additional glaciers
melted around the world, the
sea rose.
Vegetation and
animals that had been
driven south, returned to the barren-post
glacial area.
Humans arrived.
They were driven
from coastal areas and river valleys along now-submerged
former coastlines, as the
rising sea covered the
continental shelf and eventually filled
Narragansett Bay.
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You
can start with an introductory
"Prelude"
Or
click on this link for a page
that begins with formation of the
land that has become Jamestown
Rhode Island
Avalonia
More than
550 million years ago,
Rhode Island was part of
a micro-continent named
Avalonia, which formed
off of Africa and South
America, far south of the
equator.
Avalonia drifted north
and west, toward Proto
North America.
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Or,
go directly to any of our
Geological History pages:
Special
Overview Page!!
Building
the Northern Appalachian
Mountains and New England
The
Appalachians are a
complex mix of mountains
formed by a series of
continental collisions
that took place over a
period of more than 1
billion years..
This page illustrates
what was happening at a number of
important event milestones.
A set of illustrative cross
sections portray the cumulative effects
of multiple events along a line from
southern New York to Cape Cod and
beyond. Links on this page will
take you to other pages containing more
information on each event.
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Jamestown
RI - Rhode Island Visitor
Information Home
Updated 2016. Direct
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