Name: _____________________________
Date: ____________________
Science period: _______
Connecticut Landscapes and Geological History
The map below shows the terranes that make up Connecticut. A terrane is made of bedrock
that is similar in origin. In other words, the bedrock, or rock that connects Connecticut to the
lithosphere, in Proto-North America is different from the underlying bedrock in Avalonia and
Iapetos and Newark.
Consider the following information:
Proto-North America is predominantly made up of marble, gneiss, and schist.
Iapetos is predominantly made up of schist and gneiss.
Avalonia is predominantly made up of gneiss.
Newark is predominantly made up of basalt, sandstone and shale.
Proto-North America is the oldest of the terranes in Connecticut.
The Iapetos terrane was once one continuous land mass.
The Avalonian terrane was added to the Iapetos terrane before the Iapetos became
divided.
The Newark terrane is younger than the other three terranes.
All of the terranes are covered with till left behind by recent glaciers.
Work with two or three classmates to use the information above, as well as your knowledge
and understanding of plate tectonics and weathering, erosion, and deposition, to write a
sequence of events that is a reasonable explanation of what happened geologically to form
Connecticut.
Name _____________________________
Date ______________________________
Teacher ___________________________
Class Period ________________________
A Summary of Geologic Events That Formed Connecticut
Refer to the map below showing Laurentia, the Iapetos Ocean, Avalonia, and Gondwana.
http://jgs.lyellcollection.org/content/168/4/851.abstract
Before Pangea formed, the land that makes up Connecticut today was located on the shore of
the landmass called Laurentia along the Iapetos Ocean. At that time, Connecticut was located
south of the Equator!
Find the Equator on the map and highlight it or draw over it with a colored pencil.
Place an asterisk * where Connecticut may have been located and label it Connecticut.
Draw a star on the South Pole.
During the Cambrian period, when CT was located along the shore of the Iapetos, oceandwelling sea organisms lived and died. The shells sank to the bottom of the ocean and over
time became compacted and cemented into limestone.
The marbles of western Connecticut, called the Stockbridge Marbles, are the metamorphosed
remains of limestone. This marble is found among the schist and gneiss that make up ProtoNorth America.
Three convergent boundary events took place as Pangea was forming. Each convergent
boundary event created mountains in Connecticut. The process of forming mountains in this
manner is called an orogeny. The earliest event was the Taconic Orogeny, then the Acadian
Orogeny, and finally the Alleghanian Orogeny.
The first two orogenies created what is known as the Iapetos terrane. These two events were
each the result of a string of volcanic island arcs that drifted into Laurentia and became part of
what is now Connecticut as the Iapetos Ocean was subducting under Laurentia. Note: Neither
of the two volcanic island arcs are shown on the map above.
The Alleghanian Orogeny occurred when Avalonia smashed into Laurentia, the way India
smashed into Asia. This event created the Appalachian Mountains which were once two miles
high.
By the end of the Alleghanian orogeny, Pangea was complete. Once Pangea was complete, it
started to drift apart.
When Pangea started to break up, it almost split Connecticut in the middle of the state! The
Central Valley was formed when Connecticut was rifting apart. At that time, lava was flowing
along a north-south line in Connecticut the way lava flows from the mid ocean ridge! This basalt
forms high ridges in the Newark terrane. Perhaps you have seen parts of the ridge, such as
West Rocks Ridge near New Haven or the one called Sleeping Giant.
Luckily, the divergent boundary in the middle of Connecticut did not continue to rift; instead,
Connecticut rifted along the eastern shore. Evidence comes from the observation that there are
rocks in the Avalonia terrane that are the same type and age as rocks in Morocco. Half of
Connecticut almost wound up in Africa!
Throughout the eons, weathering, erosion and deposition are ongoing processes that change
the landscape or terrain. When the glacier that covered Connecticut receded about ten to fifteen
thousand years ago, the sand, pebbles, rocks and boulders that were frozen in the glacier got
dumped wherever the ice melted. The once-towering Appalachians have eroded and the
sediment that filled the central valley in Connecticut has helped form rich farmland. Soil that
has formed on top of the bedrock does not necessarily cover the bedrock evenly. Even so,
Connecticut still has many hills that run north-south because of the mountain building that
occurred during plate tectonic events. Early settlers in Connecticut built roads leading northsouth because that followed the topography of the land. The roads that connect east-west were
much more difficult to build. This is true because the terrain reflects the terrane.
Enjoy your next adventure outdoors!