As part ofNew England,Connecticut has undergone much geologic change shaped byplate tectonics,volcanism, andglacial activity.
During the earlyTriassic period, the super-continentPangea was formed as theIapetus Ocean closed up and theproto-North American continent collided withAvalonia, part of modern-dayAfrica. This caused great uplift and the formation of theAppalachian Mountains, which, at the time, were bigger than modern-dayHimalayas. Erosion of theAppalachian Mountains now exposesmetamorphic rocks once very deep in the Earth'smantle and uplifted during this time period.
About 200 million years after this collision and the formation of Pangea, during the middle of the Mesozoic Era, theAtlantic Ocean floor started spreading and great extensional forces were experienced, resulting infaulting. Connecticut'sEastern border fault was formed, a fault which begins inNew Haven and stretches 130 miles up toKeene, New Hampshire. As a result, the land west of this fault was downset, resulting in arift valley and causing the land to tilt an average of 15 to 25 degrees. The fault is currently inactive. The formation of this basin eventually refilled with soft fluvial and alluvial sediments.
DuringIce Ages,glacial activity shaped much ofNew England’s landscape, eroding mountains, leavingglacial till scattered everywhere, and forming glacial lakes. At its greatest extent, one of these glaciers left behind amoraine which became today'sLong Island. One of the biggest glacial lakes of the time was GlacialLake Hitchcock. It formed when theLaurentide Ice Sheet retreated andglacial meltwater began to accumulate at the glacier's terminalmoraine inRocky Hill, Connecticut and back up into theConnecticut River. The glacial lake left behind a soft,varved landscape, gatheringsilt and sand in the summertime due to the influx ofglacial meltwater and clay in the wintertime as the lake froze until it was later drained.
This soft surface has since beendowncut, resedimented and oft flooded by theConnecticut River, making it a very soft, nutrient-replenished area and host to the majority of Connecticut's farmland soils. The land on either side of theConnecticut River Valley is less suitable for farmlands. The eastern section holds the shallow Proto-North AmericanTerrane while the western section contains the Iapetos and AvalonianTerranes, which still holds remnants ofglacial till and lack the softfluvial sediments so prominent in theConnecticut River Valley region.
Geographic data related toGeology of Connecticut atOpenStreetMap