The Geological History of Connecticut Presentation for Hillcrest Middle School Grade 7 January 15, 2013

The Tectonic Plates Today 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

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

Different parts of Connecticut Came from Different Places Iapetos= Former Ocean Newark= Connecticut Valley Proto North America= Former Continent Avalonia= Former Continent 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

200 million years ago - Today Weathering, 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.

During the last Ice Age (about 20,000 years ago) - an ice sheet covered much of the northern part of North America, and all of Connecticut. It has been estimated to have been more than a mile thick. http://academic.emporia.edu/aberjame/ice/lec01/icegl2.gif http://academic.emporia.edu/aberjame/ice/lec01/icegl2.gif

Ice Sheet Greenland Today To get a sense of what the ice sheet might have looked like, here is a photo of an ice sheet in Greenland. It is nowhere near as big or thick as what covered Connecticut during the last Ice Age, but it gives you an idea. Remember that these ice sheets move. Greenland Today

And when the ice moves over rocks, it scrapes away at the rocks And when the ice moves over rocks, it scrapes away at the rocks. It doesn’t shave them down completely, but grinds away at it over time, helping to shape the landscape we see around us today. 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 Here are some photos of what the glacier has left us. (UL)- glacial striations (scrape marks) on bedrock surfaces. Formed by rocks embedded in the ice, scraping the bedrock while the glacier advances. The orientation of these striations tells us the direction of movement of the glacier (UR)- Till deposits- A blanket of poorly sorted ground-up rock debris, set down by the ice sheet (formed at the base and within the glacier). (LL)- Well sorted sands, gravels, and clays deposited in glacial meltwater streams and lakes, sorted by the moving meltwater. These deposits can be hundreds of feet thick. (LR)- Boulder fields formed at the end of the glacier, when advancing and melting of the glacier are at about the same rate (stagnant ice). The finer material between the boulders is washed down stream by the glacial meltwaters, leaving a wall of boulders at the leading edge of the retreating ice. All these types of glacial deposits are the parent materials of our modern soils. Source: Stone J.R. et al, 2005, Quaternary Geologic Map of Connecticut and Long Island Sound Basin, U.S. Geological Survey, SIM 2784, 1:100,000 scale 2 sheets, 76p. booklet

Connecticut Glacial Retreat – moraine ages We can see the remnants of the melting continental glacier in the glacial sediments left behind. Moraines are mixed grain-size linear mounds of glacial debris left by a glacier. These end moraine deposits are marked by accumulation of boulders left where melt-waters of glacial ice rapidly washed away smaller size debris at the end of the glacial ice. This map shows the ages of primary end moraine deposits left by the most recent northward retreating glacier. The green and blue areas illustrate the locations of major glacial lakes, created by the melt-water of the receding ice. Source: Stone J.R. et al, 2005, Quaternary Geologic Map of Connecticut and Long Island Sound Basin, U.S. Geological Survey, SIM 2784, 1:100,000 scale 2 sheets, 76p. booklet