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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
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
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 .