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The landscape of the Peace River Area
(including the watershed of the
Peace River) is very young: it formed as the ice of the
last glacial period melted away 12,000 to 8,000 years ago. Before that, our
region, as the majority of
North America, was covered with an ice sheet up to 3 km
thick. However, in some parts of the Peace Region the glaciers never touched.
One such area is the Kleskun Hill just northeast of
Grande Prairie. The thick ice sheet scoured
the land, and upon melting deposited sediments called glacial till up to 100
meters thick. The hills, rivers and valleys are all the results of the
glaciers sculpting the surface as the ice sheets grew and ultimately receded.
The region has little exposed rocks of
earlier ages except for the outcrops that have been cut by the rivers.
Most of the rock exposures tend to be along river and creek valleys.
The geology of the region can be mapped using these outcrops together with the
results of sub-surface drilling.
The rocks underlying the glacial
sediments in the Peace River Area were formed in the Tertiary and Cretaceous periods. In a
simplistic view, the rocks exposed from the
Kakwa
River to
Spirit
River are predominately Late
Cretaceous non-marine rocks. (“Late Cretaceous” refers to rocks that are 99 to
65 million years old.) These sedimentary rocks were a
result of an enormous deltaic environment. Rivers flowed from the emerging
Rocky Mountains in the west towards the east into an
inland sea.
This rock unit of deltaic origin,
called the Wapiti Formation,
has been measured up to 1500m thick in
some places. It
consists of a series of cyclical packages of mudstone, siltstone and
sandstone.
There are three coal measures that define units
within the Wapiti Formation: Red Willow, Cutbank,
and the Kakwa coal measures.
These sediments are all indicative of a swampy delta environment.
Fossils are the other clue that
geologists use to identify the environment. Plant fossils
found in the
Wapiti Formation, such as conifers, cycads and ferns all indicate
a warm, lush environment. A current
analogy may be the
west coast of
British Columbia. Numerous vertebrate bones
are also found
throughout the Wapiti Formation. Dinosaur remains include:
track ways, bone fragments, articulated
skeletons and a world class bonebed.
By correlating the rocks and fossils, a picture of the Cretaceous
period may be constructed. Our area was a large, low-lying
drainage basin with numerous swamps
and lakes. It was
heavily forested with conifers, cycads and ferns. Rivers
originated in the rising
Rocky Mountains to the west, and were flowing toward
the
Bearpaw
Sea (an inland sea) in the east.
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