The Geological History of Connecticut

Presentation for Hillcrest Middle School Grade 7

January 15, 2013

From: The Influence of Geology on the Connecticut Landscape Photo Essay by Ralph Lewis, Retired Connecticut State Geologist http://www.wesleyan.edu/ctgeology/CtLandscapes/CTlandscapes.html

The Tectonic Plates Today

1 Billion years ago - 200 million years ago (Mya)

From: The Influence of Geology on the Connecticut Landscape Photo Essay by Ralph Lewis, Retired Connecticut State Geologist http://www.wesleyan.edu/ctgeology/CtLandscapes/CTlandscapes.html

750 million years ago (Precambrian time), the east coast of North America was at westernmost Connecticut. Everything to the east was added later on, piece by piece, as continents collided, and closed up the Iapetos Ocean. The continent of Pangea was created.

About 200 million years ago, Pangea began to break apart and the Atlantic Ocean was born.

The Appalachian Mountains may once have been as high as the Himalayas!

Folded gneiss, northwest Connecticut http://www.neman.org/gsm/photos/39774-awesome-pictures.html

As the Atlantic Ocean grew, other large cracks or rifts formed in the Hartford Basin. Lava flooded into these basins.

These ridges in New Haven are the remnants of magma that flowed through the rifts and flooded the area. This

is East Rock.

Rifting occurred throughout Jurassic time (213- 144 Ma), alternating with quiet times where hardened lava and other rocks were eroded and deposited in many layers.

Intersection of Rte. 9 & 72, Berlin

From: The Influence of Geology on the Connecticut Landscape Photo Essay by Ralph Lewis, Retired Connecticut State Geologist http://www.wesleyan.edu/ctgeology/CtLandscapes/CTlandscapes.html

Different parts of Connecticut Came from Different Places

Iapetos= Former OceanNewark= Connecticut ValleyProto North America= Former ContinentAvalonia= Former Continent

200 million years ago - TodayWeathering, Erosion and

Deposition of rocks and sediments in Connecticut

Some geologists believe that up to 30 km (18.63 miles) of the bedrock cover has been removed from Connecticut during this period!

Rocks that were more resistant to erosion (harder) became the ridges and high points of land we see today.

Old Mine Park, Trumbull

Indian Well Falls, Shelton

Areas with many faults and fractures, or less resistant (softer) bedrock became the south-draining valleys and lowlands.

Connecticut River, East Hampton

Stream deposition at Savin Rock, West Haven

26,000 years ago – 15,000 years ago

While the forces that created the bedrock of Connecticut were occurring over hundreds of millions of years, smaller cycles of glacial warming and cooling were occurring every 200,000 years or so.

The northern half of most of North America has been covered by a continental ice sheet up to 2 miles thick! This happened 4 times over the last 2 million years!

26,000 years ago (Pleistocene times), the ice sheet was thick enough to completely cover Mt. Washington in New Hampshire.

http://academic.emporia.edu/aberjame/ice/lec01/icegl2.gif

Greenland Today

Ice Sheet

Glaciers move over the land, scraping away rocks and transporting sediment

15,500 years ago, the ice sheet had nearly melted out of Connecticut.

Evidence of glaciation can be found throughout the state.

End Moraine at Silver Sands State Park in Milford

Striations or scratches on West Rock Ridge in New Haven

Glacial erratic boulders in Ledyard

Glacial Evidence & Deposits in Connecticut

Connecticut Glacial Retreat – moraine ages