GEOLOGIC STORIES: DEEP TIME IN THE CONNECTICUT VALLEY
In the beginning God created geology. In the instant of the Big Bang, elements flew outward toward what would be, 13+ billion years later, the Connecticut River Valley. The Big Bang was the beginning of time as we know it, and the producer of the earliest ingredients of "everything," from humans as well as all the rocks and landscapes we see as we drive, hike, or paddle in the watershed.
While the Big Bang occurred in the range of 13 billion years ago, the Earth and our solar system sister planets coalesced from cosmic dust and gas about 4.5 billion years ago. In this early chapter of Earth time, our world encountered many meteorite impacts including a collision with a Mars-sized object which ripped a massive amount of the early earth’s volume into near-space to form the moon. Dense elements settled toward the earth’s center while lighter ones, such as form the familiar minerals quartz and feldspar, floated to the surface. Continents developed as patches of the newly cooled crust floated around like dumplings in a stew. As dumplings bumped they stuck together gradually forming continents. Geologists can easily see the remains of the older “dumplings”. They are the very old igneous and metamorphic cores of all continents.
While we are on the topic of “old”, consider the concept of a billion. This huge number is encountered in so many places: geologic time – a few billion; the budget of Massachusetts– a few 10’s of billions; the budget of the USA – thousands of billions (“trillions”). Everyone can grasp the concept of seconds of time passing. Imagine a billion seconds. How many years of time is this? Well, you can easily do the calculation and come up with a bit under 32 years. That’s 32 years! A billion dollars is a lot of cash and a billion years is a lot of time for geological change.
The oldest rocks in western New England are just over one billion years old. They are the deep-seated rocks of old granite magma chambers and metamorphosed sedimentary layers now exposed by erosion. These are “exotic terranes,” pieces of continents that drifted in from elsewhere, perhaps Africa and South America. (Both of these were, at this time, part of a huge southern continent called "Gondwana"). “Dumplings” from around the world make up the basement foundations of New England. The exciting conclusion of this confluence of Earth’s crust is the creation of Pangea. Pangea a super "supercontinent" formed as Gondwana collided with eastern North America. All land was now connected and the collision forces squeezed up the Appalachian Mountains. The geologic watch says "Permian, end of the Paleozoic". New England is now as landlocked and as surrounded by mountains as Tibet.
After several tens of millions of years the mountains are worn down by erosion. The Pangea supercontinent is also changing. As we enter the Mesozoic Era of geologic time, 245 million years ago, Pangea is beginning to split, setting the stage for the Atlantic Ocean to begin.
Living amidst a breaking continent is exciting and beautiful! The landscape looks like the Southwest’s Basin and Range topography. There are earthquakes and volcanic eruptions, although no huge volcanoes like Mt. St. Helens or Hawaii. The eruptions produce some hundred-or-so foot high cinder cone volcanoes but mainly great volumes of molten lava cover the landscape. They are called “flood basalts” or “fissure flows” and are part of the largest outpouring of lava found on Earth ("CAMP" - Central Atlantic Magmatic Province). Over a period of 600,000 years, about 201 million years ago, three major lava episodes poured about 1000 feet or more of basalt over eastern North America and adjacent pieces of Pangea, now Europe, Africa, and South America. As Pangea continued to crack apart, ocean water flowed into a basalt-floored valley east of Boston. This valley became the new Atlantic Ocean.
The Connecticut River’s watershed also begins as Pangea splits. A rift valley develops along a prominent fault line along the eastern side of the Valley appropriately called the Eastern Border fault. It can be traced from the outskirts of Keene, NH and out to sea east of New Haven, CT. Movement along the fault amounts to as much as 6 miles of offset. That’s a lot of earthquakes over its 60 or so million years of activity! The ancient Connecticut River drainage flowed down this rift valley and eventually into the newly opening Atlantic Ocean. Dinosaurs walked along the shorelines of rivers and lakes of this ancient watershed and today their footprints are prized finds in sedimentary rock layers in Massachusetts and Connecticut. Balls of mud rolled down streams and became armored with sand and pebbles. Today these rare armored mud ball sedimentary features are preserved in a few sites along the Connecticut River in and adjacent to Turners Falls, MA. See this web site's Armored Mud Ball topic.
Analysis of fossils (dinosaurs, pollen, fish) tell us that the Connecticut Valley sedimentary rock layers are from the early Mesozoic Era’s Triassic and Jurassic Periods. To be even more specific, analysis of the decay of radioactive minerals that crystallized in the lava tell us that the basalt flows are 201 million years old. In adjacent sedimentary layers it is even possible to see cyclical climate changes due to our position relative to the sun (Milankovich cycles) on a scale of 10’s of thousands of years! This ancient climate information is preserved in the sediments of lakes that swelled and deepened during wet cycles and dried to salt flats during droughts.
It is important to know not only where we were in time, but also in space. Where was our watershed on the Earth? Through the analysis of rock magnetism preserved in both lavas and sedimentary layers our ancient latitude can be determined. The watershed was 15 degrees north, tropical…like Mexico. The dinosaurs would have been very happy in this environment.
With the opening of the Atlantic Ocean eastern North America’s watersheds become flattened by river erosion. The resulting sand and mud that is eroded, is brought to the Atlantic to build beaches and the continental shelf offshore. Topographically it is a boring, flat-land time, much like being in Florida. The warm climate even resulted in a late Mesozoic barrier reef, similar to Australia's, but it is now dead and buried deep in the offshore deposits. Oil and natural gas reside here, sometimes in commercial quantities. Canada has Atlantic Ocean oil production as does the North Sea, along the other Atlantic margin to the east.
As deep time reaches the present day we have the geologic shaping by glaciers over the past 2 million years. The last glacial maximum, a mere 20,000 years ago, completely covered the Connecticut River watershed and deposited the grand terminal moraines that form the bulk of Long Island, Martha’s Vineyard, and Nantucket. Glacier-carried deposits provide the wonderful mica-sparkling beach sand found all across New England, which is much more interesting than the bland, white, quartz-only sand of much of Florida.
Finally, as our geology story winds down, the glacier retreats as melting increases. Stony glacial till is deposited across the land, the raw materials for New England’s scenic stone walls. Glacial lakes are formed as drainages are blocked by glacial and meltwater deposits. The most important of these is glacial Lake Hitchcock that followed the Connecticut River Valley from Middletown, Connecticut to West Burke, VT and Littleton, NH. Deposits in this lake provide abundant sand and gravel resources for septic systems and roadways as well as aquifer recharge due to its ability to absorb rainfall.
Humans are making their impact as geologic time marches on, but our scratchings will be just a temporary imprint in deep time history. The next glacier, coming in several 10’s of thousands of years, will definitely cause the evacuation of all New England. Where will our descendants go? Probably to Florida where they will enjoy a milder climate than the glacial Northeast, but they will have to stroll along beaches of bland quartz sand. No shiny mica for them, but that sounds like a good trade-off to me.