The Cretaceous World
This is the last period of the Mesozoic Era. The Cretaceous
follows immediately after the Jurassic Period and it is followed by
the Paleogene Period of the Cenozoic Era. It is
also better known as the final era of the dinosaurs. A huge
mega-worldwide extinction event, ocurred approximately 65.5 million
years ago, wiped off in mass scale most animal and plant species in
a geologically short period of time. A period with a relatively
warm climate and high sea levels, the Cretaceous'
oceans and seas were populated with now extinct marine
reptiles, and the land by dinosaurs.
The Cretaceous Era is divided then into an Early and a Late
Epoch. The Paleontologists researching the area estimated that
these tracks were made in the Albian Age, the last age of the Early
Cretaceous Epoch. Pay attention and read the signs posted at the
cache location to tell me how long ago (in millions of years) do
the researchers estimate these tracks were made?
The Western Interior Seaway
If you have ever asked yourself as I did too how it was possible
to find fossilized seashells in the Rockies and all along the
Central Plains. Then the answer is that millions of years ago most
of what we know as the Central North American Region on the eastern
side of the Rocky Mountains was underwater.
The Western Interior Seaway was created when two big tectonic
plates collided. The North American and the Farallontectonic plates
collided, causing the Rocky Mountains to start raising on the
western side of the early young continent. While on the central
region a shallow depression started to get flooded due to high sea
levels. Known as the Eustatic Sea levels existing during the
Cretaceous, it allowed water from the Arctic Ocean in the north and
the Gulf of Mexico in the south to meet and flood the central
lowlands of North America. As the Farallontectonic plate kept
pushing underneath the North American plate uplifting the Rockies
higher, this 1,000 miles in diameter seaway grew and receeded over
the course of the Cretaceous.
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Western Interior Seaway during the mid-Cretaceous, about 100
million years before the present
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At its deepest, it may have been only 800 or 900 meters deep,
shallow in terms of seas. Two great continental watersheds drained
into it from east and west, diluting its waters and bringing
resources in eroded silt that formed shifting delta
systems along its low-lying coasts. Along the western shore of the
seaway many rivers and waterways easily flooded in and out of the
calmed mass of warm water. There was
some sedimentation on the western shores of the Seaway
where the actual Colorado state eastern side of the Rockies are, as
shown on the map on the right.
Dinosaur Footprints and Tracks
As we already know the high eustatic sea level and the warm
climate of the Cretaceous meant a large area of the continents was
covered by warm shallow seas. This facilitates the proliferation of
coastlike vegetation along extensive shallow beaches and river
mouths. Reading the signs posted at the cache's location tell me
what type of geographical feature do the researchers believe these
dinosaurs were wandering on? Look for and think of a type of body
of water like a bay, a beach, a gulf, or a delta for example.
Dinosaurs walked deep into these shallow waters to find grazing
water pastures and to escape from predators.
An interesting characteristic of the Cretaceous Era is the
proliferation of a particular type of rock. The Cretaceous was
named for the extensive chalk deposits of this rock in many parts
of the world. Cretaceous means "chalky" in Latin and it consists
for a major part of marine limestone, a rock type that is
formed under warm, shallow marine circumstances. Due to the high
sea level there was extensive accommodation space
for sedimentation so that thick deposits could form.
Because of the relatively young age and great thickness of the
system, Cretaceous rocks crop out in many areas worldwide.
The bottom of the Western Interior Seaway was made in part of
big deposits of this chalky rock. Calm water allowed sediments from
the top to easily sunk to the bottom increasing its layer through
millions of years. Through this sedimentation process the bottom of
the seaway was slowly transformed into a huge blank ready to be
imprinted. Different land animals that approached the water to
drink or eat the plants left their footprints on the chalky bottom.
Eventually after millions of years the seaway was slowly drained
through east and west watersheds leaving behind a thick layer of
chalk and sediment. Once exposed to the sun and atmospher it
quickly drained and solidify preserving most of what was buried and
covered by the sediments.
Geography of the US in the Late Cretaceous Period
By the period when these tracks were made this area was on the
edge of the Western Interior Seaway, a group of dinosaurs were
walking side by side through the mud along together probably eating
the plants. Can you tell me what type of dinosaur left the
footprints? Their tracks then were slowly filled in by silt, sand
and plant debris, which later hardened to preserve everything in it
as casts of the actual tracks.
Dinosaurs walking on the Skyline
The final stage of this process occurred with the uplift of the
Rocky Mountains. When two tectonic plates collide the edge of one
is uplifted while the edge of the colliding plate is subsidenced
underneath the other plate. The Rockies have an orogenic uplift as
the result of tectonic plate collisions and results in mountain
ranges or a more modest uplift over a large region. After the
Western Interior Seaway was completely drained the seaway's bottom
started to be uplifted along the mountains. After the sediments
were deposited, the walls of the basin were raised by the Rocky
Mountain uplift that tilted the rocks on edge. This explains why we
see these unexpected “footprints” on the rocky wall.
Looking at the footprints on the ridge wall, tell me from what
point of view you are seeing the footprints and how many tracks you
can count.
Around December of 1999 a paleontology student at the university
of Colorado made the astonishing discovery. He was taking a walk
along Skyline Drive when he noticed what he thought were dinosaur
tracks on the wall of the ridge. He reported the find to the
curator of the Dinosaur Depot. They both together came back to the
location to survey the tracks. Look at the signs in the area and
tell me the name of the paleontology student who discovered these
tracks.
To receive credit for this earthcache:
Post a picture of you with your GPS receiver and the
Dino-Trackway in the background and answer the five questions I
have asked you along the cache's description article.
* Please email the answer to these questions (using my profile
link) - do not post the answers in your log.
Enjoy your visit to this unique location!!!