Many geologists have referred to the AA Highway as a “treasure
trove” and “an outdoor classroom” in which to study diverse and
significant features such faults, systemic rock boundaries, fossils
and ancient river markers.
Like modern-day sleuths, geologists interpret the clues they
find preserved in the rocks. These clues are of two main kinds: the
types of fossils contained in the rocks and the properties of the
rocks themselves. As geologists' knowledge of the Earth increases,
the record of its history has become clearer and more
meaningful.
Buckle your seat belts and head back in time and look for the
clues as you head down the AA from it’s intersection with US 23 in
Greenup County. Each cache in this series will stop at a unique
geologic formation and will seek answers to some basic questions
that should be easy to calculate. Sizeable pull off areas are
available at each stop in the series. Geology students frequent the
locations routinely. The calculations can be made from your car
even, making it handicap accessible!
Travel to Mile Marker 8.3 where the AA Highway intersects with
Liberty Road and take a trip to the Quaternary Period…
The Quaternary Period of geologic time is comprised of two sub
periods, the Pleisticine and the Neogene. The Neogene occurred 23
million to 2.6 million years ago and the Pleisticine began 2.6
Million Years Ago and continues here in the present. The Holocene
Epoch discussed here is an epoch of the Quaternary Period that
refers to the most recent period of time. It is a sub group of the
Neogene. Climate change and the developments it spurs carry the
narrative of the Quaternary, the most recent 2.6 million years of
Earth's history. Glaciers advance from the Poles and then retreat,
carving and molding the land with each pulse. Sea levels fall and
rise with each period of freezing and thawing. During warm spells,
the ice retreats and exposes reshaped mountains striped with new
rivers draining to giant basins Some mammals get massive, grow
furry coats, and then disappear. Humans evolve to their modern
form, traipse around the globe, and make a mark on just about every
Earth system, including the climate.
Since the outset of the Quaternary, whales and sharks have ruled
the seas. On land, the chilliest stretches of the Quaternary saw
mammals like mammoths and mastdons don shaggy coats of hair. About
10,000 years ago, the climate began to warm, and most of these
giants went extinct. Only a handful of smaller, though still
impressively large, representatives remain, such as Africa's
elephants, rhinoceroses, and hippopotamuses. Scientists are
uncertain whether the warming climate is to blame for the
extinction at the end of the last ice age. At the time, modern
humans were rapidly spreading around the globe and some studies
link the disappearance of the big mammals with the arrival of
humans and their hunting ways.
After the last ice age, when the great melt occurred there were
valleys created like this Quaternary Period Valley here along the
AA Highway. Quaternary Geologists can reconstruct a valley's
history and provide a detailed chronology of stream histories based
on it's sedimentation. When river erosion cuts through or there is
additional uplift, the current flood plain is abandoned and the
river incises deeper, down cutting it's river bed to create a lower
flood plain. The abandoned flood plains at higher elevations are
called terraces. These terraces over time become filled with
alluvial materials cast off from many periods throughout geologic
time of ice melt and channel cutting. Five times during the
Quaternary Period ice froze then melted washing new materials into
new channels cut from the volume and velocity of streams.
Alluvial materials are stream deposits and sediments that have
built up over millions of years of time. They create a terrace from
the sediment build up.
Meander when related to streams is an extreme U-bend in the course
of a stream, usually occurring in a series that freely adjusts its
shape and shifts downstream according to the slope of the alluvial
valley.
As the last Ice Age began to cool the Earth and large glaciers
began to creep south from modern-day Canada, many landforms and
features were changed or destroyed, including the Teays River. The
nearby Tygart Creek was a main tributary to the Teays River that
flowed northward prior to the tilt of the land when the Appalachian
Mountains were formed and the deep drainage period following an ice
age thaw.
The abandoned Tygart River meander is clearly visible from the
AA highway.
The Quaternary geologic feature to study here is the modern
landscape which became a roughly flat-bottomed, broad semicircular
depression type valley with a pronounced relict meander of the
ancient Tygart Creek of 2 million years ago . When the last ice age
10,000 years ago drained and new courses for streams were cut, the
Tygart channel here was cut much deeper. Note the new stream
channel brought on by geologic change here in this quaternary
valley of alluvial material.
The abandonment is entrenched into the upper Pleistocene terrace
unit and bounded to the north by the terrace scarp. The scarp
enclosing the abandoned meander separates the upper-Pleistocene
terrace alluvium from the Holocene one and is well-preserved, with
a sharp upper edge and scarce colluvium/debris accumulation at the
toe. Today part of the relic is being used as a farm pond.
Pleistocene glaciers made important alterations in the
topography of the glaciated regions, leveling hilly sections to
low, rolling plains, both by erosion and by deposition of drift,
eroding hollows that later became lakes, and forcing rivers to cut
new channels by filling their former beds.
Below are the instructions for your mission. Email the answers
for the questions below . Post a picture of the meander with your
log that shows some of this fairly new valley per geologic time.
Now you are a geocaching geologic sleuth!
Mission:
1. Mark a point on your GPS at the abandoned meander across from
the Liberty Road Intersect.
2. Travel down the road to where the modern day Tygart Creek flows.
3. Calculate how far from it’s relic course it is today.
4. Shoot an elevation of this Quaternary Valley.
Questions:
1. How far from the abandoned meander is the modern stream bed?
a. 2/10ths of a mile
b. 3/10ths of a mile
c. 4/10ths of a mile
2. What is the elevation of the valley floor?
Most of the quaternary period rock is of great economic value.
Sand, gravel, clay, and ground water from fluvioglacial and
alluvial deposits are the most important mineral commodities in
Pleistocene and Holocene sediments in Kentucky. Sand and gravel are
second in importance as a source of mineral construction material.
Alluvial and residual clays were the earliest sources of brick clay
in Kentucky and have been used, or are being used, at scattered
localities for the manufacture of brick, field tile, and portland
cement.
The character and progress of a people are influenced by the
soil on which they live. The life of the inhabitants of a region is
largely determined by the character of the hills over which they
roam or of the fields on which they toil. Geological influences,
both through the formation of soils and through deposits of rich
mineral resources have greatly influenced the industry of people
and the course of history.
Now buckle up and get ready to head on down the AA Highway on
another trip back in time!
