Geological History of Jamestown, Rhode Island

Pangaea Breaks Up

Atlantic Forms, Appalachians Erode

The Mesozoic Era means "middle animals", and is the time during which the world's fauna changed drastically. The era is divided into three time periods: the Triassic, the Jurassic , and the Cretaceous .

The Triassic, 248 to 206 million years ago, was a time of transition. Triassic organisms belonged to one of three groups: survivors of the extinction, new groups which flourished briefly, and new groups which went on to dominate the changing world.

Pangaea began to break up about 200 million years ago.

During the Jurassic, 208-146 million years ago, dinosaurs dominated the land, the first birds appeared, and small rat-sized animals became the first mammals. Ferns, ginkgoes, bennettitaleans or "cycadeoids" and cycads flourished; conifers were also present. In the sea, cephalopods, sharks, rays and giant marine crocodiles could be found.

The North Atlantic Ocean formed as North America separated from Africa, Europe and South America. As North America pushed westward, the west coast entered a period of new tectonic activity.

As the continents separated, portions of the eastern Avalon Terrane pulled away from North America; eventually becoming southern Ireland, Wales, southern England, parts of Portugal and Spain, northern France, Holland and Germany.

Similarly, portions of the coast of Africa were pulled away by North America. Most of the land east of the Appalacians and south of Long Island was previously part of Africa.


Wind, rains, freezing, thawing and other phenomena eroded the once-massive Appalachians.

Particles generated by weathering were carried by streams, rivers and wind to lower elevations.

This sketch by Dr. Ralph Lewis, shows build-up of sediment south and east of the mountains forming the Atlantic coastal plain on top of older bedrock along the Connecticut coast. The layers of sediment extend undersea onto the continental shelf.

The Cretaceous, 146-65 million years ago, saw the first appearance of many modern lifeforms - flowering plants and the co-evolution with animal pollinators, butterflies, aphids, grasshoppers, gall wasps, termites and ants.

The breakup of Pangaea led to increased regional differences in floras and faunas between continents.

Mass extinctions mark the end of the Cretaceous Period, 65 million years ago. The dinosaurs died out, along with the marine reptiles such as the ichthyosaurs, plesiosaurs, and mosasaurs, and the pterosaurs;. yet other groups of organisms, such as flowering plants, gastropods and pelecypods (snails and clams), amphibians, lizards and snakes, crocodilians, and mammals survived.

The Atlantic Ocean is still growing, some 180 million years after it began to open. Animation of the growth of the Atlantic Ocean by Christopher Scotese.

At the mid-ocean ridge, new crust is formed via volcanic activity.  The new crust then moves away from the ridge.

The Atlantic spreading Age of seafloor The Atlantic Ocean still is growing, some 180 million years after it began to open

Proceed to the next installment of this narrative


Glaciers form and rework the land

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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