Learn About Local Geology

The above diagram shows the general geology of the area surrounding the Nash Dinosaur Track Site.
The cross section runs north to south.

ROCK LAYERS OF THE CONNECTICUT RIVER VALLEY NEAR THE NASH DINOSAUR TRACK SITE

(Layers are listed from upper to lower layers)

3. GLACIAL DEPOSITS – During the last major glacial period the glaciers stripped away the top geological sediments of the valley. Later, as the glaciers melted away, they left behind a layer of sediment on top of the underlining rocks . This layer of glacial material varies from zero to 100 feet in depth . This is the layer that makes up most of the surface of the Connecticut River Valley floor.

2. ANCIENT SEDIMENTARY ROCK LAYERS - These rock layers are made up of a series of sedimentary layers interspersed with two lava flow layers. All are laid down on top of the basement rock. It is in two of these sedimentary layers that one finds dinosaur tracks.

e. *Portland Formation* - A layer of sandstone to shale to siltstone sized particles that were laid down in an arid mud flat with oases environment. This is the layer that contains the most dinosaur tracks and skeletons. Two fragmentary theropod skeletons have been found in the Portland Formation rocks, as have been numerous prosauropod skeletons and an early crocodile. It also contains fossil fish, plants, invertebrate trace fossils, ripple marks, rain drop impressions and mud cracks. *This is the layer in which the Nash Dinosaur Track Site is located*.

d. Hampden Basalt and Granby Tuff Formations - This is the last of two basalt lava flow that make up the Mount Holyoke Range. Like the underlying Holyoke Basalt, the Hampden Basalt came to the surface and flowed out over the basin sediments before hardening. The Granby Tuff is a thin layer of volcanic ash and sediment that is intertwined with the Hampden Basalt . There are no fossils found in this formation .

c. East Berlin Formation - A layer of shale to siltstone sized particles that was laid down primarily in an arid mud flat with oases environment. There are fossil fish found in the sediments that were deposited in the ancient oasis lakes and dinosaur tracks which were formed in the lake shore deposits. This is not the layer where the most dinosaur tracks are found.

b. Holyoke Basalt Formation - This is the first of two basalt lava flows that make up the Mt. Holyoke Range. Based on its chemical composition, geologists know that it erupted more like the fast-flowing rivers of lava on the Hawaiian Islands than the highly explosive eruptions of volcanoes like Mt. Saint Helens. The lava came to the surface and flowed out over the New Haven Arkose Formation before solidifying. There are no fossils found in this formation .

a. New Haven/Sugarloaf Arkose Formation - ( North of the Mount Holyoke Range this formation is called the Sugarloaf Arkose, but on the south side, around the Nash Dinosaur Track Site and south, it is called the New Haven Arkose . ) It is a layer of conglomerate to sandstone sized particles deposited by flowing streams. The stone is often reddish in color and contains some scrappy skeletal material . Some of the fossils found in this formation are the crocodile-like phytosaur, small lizard-like reptiles, and the plant-eating aetosaurs .

1. BASEMENT ROCK - The basement rock is a complex mixture of igneous and metamorphic rock. It is made up of ancient ocean sediments and igneous rocks.

ENVIRONMENT OF THE NASH DINOSAUR TRACK SITE
AT THE TIME OF THE DINOSAURS

This is a mural of what the Nash Dinosaur Track Site looked like at the time of the dinosaurs.
It was a very different place then than what it is today.
The view is looking south toward Springfield, MA.

The Connecticut River Valley of Massachusetts and Connecticut is part of an ancient rift valley system called the Newark Supergroup . It stretches from Newfoundland, Canada to Florida, USA. This rift valley system is made up of a series of smaller rift basins that formed when the Pangea continent separated . The Connecticut River Valley is made up of the Deerfield Basin (north of the Mount Holyoke mountain range) and the Hartford Basin (south of the Mount Holyoke mountain range). The Nash Dinosaur Track Site is located at the northern end of the Hartford Basin .

The climate of the Deerfield and Hartford basins was semi-arid and hot most of the year, similar to that of the rift valley of East Africa today. However, each year there was a monsoon season that usually brought a lot of rain to the area, especially to the mountains to the east and to the west. The rain that fell in the mountains was carried into the valley in streams and as sheet floods, and at certain times it collected into large lakes that would cover much of the valley floor . (There was no Connecticut River at the time). During the dry season, the lakes would recede and the dinosaurs would have roamed the valley, leaving their imprints in the mud to harden. However, the lakes rarely completely dried up, and during the dry season remnant lakes would form oasis areas around which life would have congregated for food and water .

The mountains to the west of the valley were the early Appalachian Mountains . The mountains to the east were formed by large faults that uplifted the land to the east of the valley as the valley subsided . The sediments that filled the valley in which the Nash Dinosaur Track Site is located were eroded from these mountains east and west. The Hartford and Deerfield rift valley basins were probably bigger than what they are today. Currently, the basin is about 20 miles wide and stretches from what is today the Massachusetts and Vermont border south to Long Island Sound. In some of the valley's sedimentary layers (the East Berlin and the Portland) we find the impressions of dinosaur tracks.

Eventually the rift valley completely filled with sediment and the erosional processes slowly began to work . Much later, huge glaciers, up to 1 mile thick, moved across New England from north to south, speeding up the erosion process. The glaciers removed the upper geological layers and re-exposed the lower geological layers with the dinosaur tracks in them. However, when the ice melted, large deposits of glacial debris were left behind on top of the sedimentary rocks containing the dinosaur tracks.

Today only parts of the old mud flat layers are exposed. One place where one may find dinosaur tracks is along the edge of streams where streams have eroded down through the glacial material . Also, one may find dinosaur tracks where areas of the old mud flat layers stick up above the surrounding glacial material . This is why the Nash Dinosaur Track Site is exposed. Finally, one may find tracks where excavation work digs down through the glacial material and exposes the underlying mud flat layers .

EDWARD HITCHCOCK'S 1858
GEOLOGY OF THE VALLEY

The diagram shown above was created for the 1858 Ichnology of New England by Edward Hitchcock. The diagram runs east to west . The geology is simplistic compared to today's knowledge, but it has the right idea about a number of things .