Seven Mile Creek Earthcache
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This Earthcache will take you on an approximately .80 mile round trip walk through a portion of Seven Mile Creek, from Route 5 to Lake Erie and back.
I strongly suggest wearing high boots and maybe bringing a hiking stick to help stability. Although it is a relatively flat walk, it is very slippery. You will be walking on rocks in the creek and will encounter some deep spots and swift moving water. I have been here when the water level was low and did ok with just sneakers on…but I have also been here after a rain and definitely needed knee-high boots. The whole walk takes place in the creek, and much of the creek during this stretch goes through land owned by The Glinodo Center. The Benedictine Sisters operate the Glinodo Center and have allowed access to the creek for walking as well as fishing, but they do not want people parking on the property. There are signs there to remind you not to park on their property. You do not want to anger a nun! Parking is located at N 42 10.858 W 79 58.355. It is a small pull off area along Route 5 and is big enough for several vehicles. Enter the creek near the bridge, which is on the opposite side of the Glinodo Center driveway from the parking, and proceed up the creek to Lake Erie. This Earthcache will begin at the given coordinates.
First, let’s start with some definitions of the geologic features that you will be seeing.
An anticline is a fold that is convex up and has its oldest beds or layers at its core.
A fold is when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. Folds form under varied conditions of stress, hydrostatic pressure, pore pressure, and temperature.
A concretion is a volume of sedimentary rock in which a mineral cement fills the spaces between the sediment grains. Concretions are often spherical in shape. Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum.
One type of concretion is called cone-in-cone. They are cone-shaped forms made of rock that nest inside a cone cup. People mistake these for fossils, as they look somewhat similar to horn corals. These cones, however, have never been alive. They are usually made of rock that is both calcareous and contains clays.
The term joint refers to a fracture in rock where there has been no lateral movement in the plane of the fracture. This makes it different from a fault which is a fracture in rock where one side slides laterally past to the other. Joints normally have a regular spacing related to either the mechanical properties of the individual rock or the thickness of the layer involved.
(requirement #1 at the given coordinates)
At the beachfront access, note how rounded and broken the loose rocks higher on the banks are. Observe the color and banded patterns in the rock exposed in the bluff and at the waterline. From the water line up the bluff about four feet, the rock shows a distinct pattern of alternate black and light gray layers. Higher up, this pattern stops and the layers are thicker and of a more uniform rusty brown color. The lower striped layers are sometimes called zebra rock. They are formed from very fine sediments in areas either farther out from shore or restricted near-shore areas where heavier sediments cannot reach. The dark layers contain more organic materials and indicate stagnant, oxygen-poor water. Evidence of these conditions is confirmed by the occurrence of pyrite crystals in these layers. The upper layers of rock are composed of somewhat larger sediments, and thicker layers. This indicates that more sediments were coming in and periods of stagnation were not occurring. These layers also contain an unusual geologic formation of cone-in-cone concretions. These concretions occur in a layer at about eye level from the water line. Cone-in-cone concretions are not particularly common, but many can be found here in the North East Shales.
Depending on recent creek levels, gravel and sandbars are usually present at the mouth of the creek. These are deposited as the current strength dissipates in the lake and sediment drops out of the water. As you move upstream toward the bridge, watch for pyrite in the lower rocks at water level and cone-in-cone rocks higher up.
Under the bridge, observe the ramp-like surface of the rock and how the layers of rock are bent upward. This is one side of an anitcline, formed as rock was laterally compressed and folded. Proceed up this small ramp and look very closely at all the rock surfaces. While very few fossils occur in this section of the rock, two kinds of trace fossils, or tracks of small animals are abundant here. The smaller little lines were most likely formed by some kind of worm crawling, as they strongly resemble the squiggly lines modern worms leave in mud. The larger (wider) tracks were most likely made by some type of arthropod as it crawled around. Possible candidates for these tracks are trilobites, crabs or eurypterids.
As you approach the bend in the stream, look closely at the bank. You will notice how the rock is bent. This is a cross section view of an anticline where both sides or limbs can be seen, and parts of the crest or middle have been eroded away. Notice how the edge of the falls parallels the trace of the center of the anticline. Where the rock was broken, it provided a weak area in the rock. The moving water could more easily erode this rock and the rock downstream from the broken rock, creating this small waterfall. At the layer forming the top of the waterfall, keep an eye out for exposed cone-in-cone concretions. You will now see the top side instead of the cross sections seen in the bluff along the lake. Look for round, slightly domed, circular objects with a surface marked by many small circles. Proceed up the creek and round the bend, keeping an eye out for the trace fossils.
(requirement #2 N 42 10.937 W 79 58.746) Stretching across the creek is the crest of another anticline that actually may be a small fault. Look at the exposed west bank and the line of bent and broken rock can be seen. Note how the moving water has been able to more easily erode the broken rock through the stream-bed, creating a large pool. If not for this geologic structure, this set of falls and pool would not have formed here.
(requirement #3 N 42 10.923 W 79 58.723) At this site, a waterfall and ledge cut diagonally across the stream. This is caused by a large set of cracks in the rock that can be seen at the base of the ledge. Cracks of this type are called joints and differ from faults in that no movement has occurred on either side of the joint. Just as with faults, joints create a weak place in the rock where moving water can more easily pluck out rock from the stream bed.
(requirement #4 N 42 10.908 W 79 58.598) The footbridge provides a nice spot to see another waterfall. The intensity of rock fracturing at the crest of the anticline is severe, allowing rock to be easily eroded. It is possible that this is actually a fault. The low bank and overgrowth on the stream’s banks makes it difficult to tell if movement has actually occurred. The narrow band of disrupted rock and the intensity are very strong indicators that this is a fault. The folded rock just below the falls is bent in the correct pattern for a normal fault. However, the water and streambed rubble hide the other side, making it difficult to tell what has happened.
There are many more features in the creek bed between this bridge and Route 5. See what you can find on the way.
In order to successfully log this Earthcache as a find, you will need to complete the following requirements…
1. (the given coordinates) Take a photo of yourself and your GPS at the mouth of the creek near the lake. Be
sure to include either the rock layers or sandbar in the photo as well.
2. (N 42 10.937 W 79 58.746) Measure the depth of the pool below these falls.
3. (N 42 10.923 W 79 58.723) Measure the height of these falls.
4. (N 42 10.908 W 79 58.598) Estimate the width of the streambed at these falls.
5. Find a cone-in-cone concretion, or trace fossils, or an anticline. Measure the size of
the feature you chose and take a picture of it including your GPS in the picture. There
are many places along the way where you can find one of the items needed for this
requirement. See the attached pictures below for examples of what you are looking for.
6. E-mail me the answers to the questions and post your pictures with your log.
Additional Hints
(No hints available.)