Geological History of Jamestown, Rhode Island

Alleghenian Orogeny


Northern Alleghenies rise to new heights, PANGAEA formed

Continental movement did not cease after Baltica and Avalonia collided with Laurentia. Siberia joined with this grouping to make a configuration that has been called Euramerica or Laurussia.

The momentum of continental movement put Euramerica on a southward collision course with another newly formed continental grouping, Gondwana. Gondwanda consisted of modern Africa, South America, India, Antarctica, Australia, New Guinea, and New Zealand.

About 356 million years ago, North America crashed into Gondwana, a collision often referred to as the Alleghenian orogeny.  

The progress of these collisions is traced using modified Paleomap project drawings of the earth at 400, 380 and 360 million years ago. For reference, the J in the first drawing (400 million years ago) indictes the approximate location of Jamestown.

About 306 million years ago, the "supercontinent" Pangaea (meaning "all lands" in Greek) was formed as multi-continental collisions continued.

These continuing impacts created a vast mountain range and deformed and metamorphosed rocks previously altered by earlier mountain building episodes.

For additional, complementary information, see this link to a University of Maryland page, which also draws data from work by Ron Blakey and PALEOMAPS as well as C.R.Scotese.    The University of Maryland Historical Geology page is also available in pdf format.

In the Narragansett Bay area, folded rocks formed a large depression (or basin) during the Alleghenian Orogeny. Sediments accumulated in the Narragansett Basin, ultimately creating the upper layers of bedrock beneath most of the area. (See Guide to Bedrock)

As the continents were joining, more forms of life were appearing - club mosses, horsetails, ferns, winged insects, reptiles and gymnosperms. The Carboniferous Period occurred from about 354 to 290 million years ago. Limestone was laid down in areas covered by the sea, such as the central United States, while other areas, such as the Narragensett basin, created the basis for coal deposits where forrest, swamp and marine environments alternated as the sea level fluctuated. (A pdf version of a University of California Museum of Paleontology page on this period can be accessed here.)

The Permian period lasted from 290 to 248 million years ago. The global geography of the Permian included massive areas of land (Pangaea) and water (a single ocean, the Panthalassa, and a sea on the east side of Pangea called the Tethys). Continental collisions built mountains where lowland forests, swamps and coral reefs once flourished. Many of the world’s shallow seas became isolated and dried up. Entire ecosystems were obliterated, resulting in massive extinctions. High mountain chains blocked the flow of moisture-laden air across the supercontinent. Desert conditions prevailed across much of the midcontinent.  (A pdf version of a University of California Museum of Paleontology page on this period can be accessed here.)

The artist renderings immediately below are derived from a series by Dr. Ron Blakely, Professor of Geology, Northern Arizona University. They show the Ouachita Mountains in Oklahoma, created by impacts between Laurentia and Gondwana in and near present day Texas, Louisiana and Venezuela and the Southern Appalachian mountains, created by impacts between Laurentia and present-day north Africa.

This graphic was shows the various pieces of Pangaea about 255 Million years ago.  It was created by the Paleomap Project.

PANGAEA - 255 million years ago
Yellow = North America
Green = South America
Light blue = Africa
Red = Eurasia
Dark blue = Australia
Fuchsia = Antarctica

The sketch at right shows a close-up of the juncture of North America, Europe and Africa around 255 million years ago.

Features are identified as to the land mass they are associated with (Laurentia, Baltica, Africa). Islands and peninsulas show the origins of their parts (a combination of Laurentian land and portions of the Avalonian arc).

The Appalachian and Caledonian mountains (Greenland and Northern Europe) are identified, as they underwent orogenies during the collisions that formed Pangaea. Parts of the original Avalonian arc system are shown in shades of grey.

Land of Avalonian origin is identified as belonging to one of three groupings - Avalonia, cutting in a southwest to northeast line from Connecticut to Germany, Meguma and Cadomia (parts of Morocco, Portugal, Spain and France) and Carolina. J indicates the approximate location of Jamestown.

The end of the Permian, about 250 million years ago, marks the world's biggest extinction. The full explanation is still being sought. About 50% of all families and more than 90% of all species died out. Only one trilobite family remained and extinction of this once ubiquitous creature was close at hand.

Climates became cooler. Enormous volcanic eruptions took place in Siberia. Lowered temperatures in tropical regions may have reduced oxygen content in the oceans. Some groups of plants and animals survived the Permian mass extinction in greatly diminished numbers, but balances had changed, clearing the way for new groups of land and sea life.

Continue with the next installment of this narrative

The Atlantic Forms

Pangaea breaks up, the Atlantic forms, the Appalachians erode

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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