Sedimentology, also referred to as sedimentary geology, is the study of sedimentary deposits and their origins, deals with ancient and recent marine and terrestrial deposits and their faunas, floras, minerals, textures, and evolution in time and space.1 Sedimentologists study numerous intricate features of soft and hard rocks in their natural sequences, with the goal of restructuring the earth’s earlier environments in their stratigraphic and tectonic frameworks. The study of sedimentary rocks includes data and methods borrowed from other branches of geology, such as stratigraphy, marine geology, geochemistry, mineralogy, and environmental geology. Clay size particles are the most commonly found sediment. Yet they do not normally settle in the natural environments as individual particles. Since clay particles are usually present with other size fractions, a dispersion treatment usually goes along with any sediment preparation.2
The purpose of our lab is to determine what type of sediment whether it is fine, medium, or coarse, is deposited in different parts of the Pfeffer Park stream. More specifically, what types of sediments are found in the straight and curved areas of the stream, and what types of sediments will be found in these different areas if these areas are in the open, or covered by foliage. We also plan to determine how much sediment will flow through a certain volume of water in both rainy and dry conditions. We also plan to gain a better understanding of how sediments are distributed throughout a stream or river.
We feel that the larger sediments will be found in the straight areas because the water is not moving fast enough to carry them down stream. We also feel that in the areas that are covered with foliage there will be different types of sediments such as pieces of twigs or leaves. Lastly we feel that there will be smaller sediments because the water is moving the larger sediments further down the stream into the straight areas.
We checked out the project about sedimentation in the Duck Pond. We found that many of the same ideas that they used will also be used for our project. For example, their method of measuring velocity of the water by measuring a meter of water then timing how long it will take an object to travel that distance is the same method that we will be using.3
Our project can be used on a larger scale in areas such as river deltas to determine how quickly sediments are being deposited. For instance, using many of the same methods used in our lab, one can determine how quickly sediments are being deposited in the Mississippi River Delta.
Materials and Method
Our sampling design included placing a core, a hollow, cylindrical tube, into the sediment on the stream floors. To sample the sediments in the water we used a liter container. Once these samples were taken we took the sediments back to the lab, weighed, and sorted the sediments with a sieve. Depending on where the samples were taken the different sizes and weights will answer the question about what different sediments were in the straight or curved areas. We took measurements of water depths across the stream to find the area of a certain part of the steam. With the area and the amount of sediment in a sample of water, we were then able to calculate discharge. We involved the class by letting them weigh and sort some of the sediment samples they took. They then hypothesized about how the material got there.
For the sediment samples we took, we found three different environments. We looked for combinations of the following: shaded or not shaded and straight or curved. Then, we mapped out the areas and kept record of where we sampled. We then took five samples within each environment. Some were taken in the water, others where the water used to be. We stored these in plastic bags until it was time to analyze all of our samples. When we studied the materials, we massed them, sent them through the sieves to separate different size particles, and finally re-massed them for comparisons. We took the class to Pfeffer Park to take their own sediment samples. Then they took them back to the lab so they could analyze them and compare them to other group’s samples. This would allow them to determine if their hypothesis was correct. By allowing the other students to study our samples, they could obtain a better understanding of our lab.
For our next step, we took water samples to determine the amount of sediment in stream flow. We used the one-liter container to get one sample per environment for each set of sediment samples. We filtered the water and all its contents and massed what is left on each paper filter. For the class we provided all of the collected sediment so they can analyze them.
Our final step was to figure out the amount of sediment discharge in a given volume of water. To do this we first measured out the length of one meter of water. Then by simply placing a floating object in the water, we timed how long it took for it to go the distance of one meter. With this information we could calculate the velocity of the water. Once this was done then we continued by measuring the depths of the water in 10 places across the stream. With these measurements we drew a cross section of the bottom of the stream. With the cross section we could then determine the volume of water for the one-meter distance of water. Next was to determine the amount of sediment in the given volume of water. We did this by using the water samples used earlier. We drained the water from the one-liter sample and determined the volume of the sediments in that one-liter sample. With that we set up a ratio to find out what volume of sediment was in the given volume of water in the stream. Then by taking the volume of sediment in the water and multiplying it by the velocity of the water we determined the rate of sediment discharge in the stream.
After all was said and done we came up with some pretty interesting results. The following six graphs show the percent weight of the grain size by environment. As the graphs on the following pages show, there looks to be a significant difference between the percent weight of the grain size by environment. The strange part is that when looking at the anova test the P-value is greater than .05 so we had to accept the null hypothesis that there is no significant difference between the percent weight of the grain size in each environment. We also did a test to find the amount of sediment discharge in the water of each environment. Graph number seven shows these statistics.
Looking further at the results we found that the straight area that was shaded with foliage had the largest sediment deposition, and straight environment had the smallest sediments deposited, but there were also quite a few larger sediments. The curved area of the stream also had large sediments deposited. What this information tells us about our hypothesis is that part of it was correct while part of it was incorrect. We were correct in saying that the shaded areas would have larger sediments deposited, but out hypothesis was incorrect in the fact that we said the curved areas would have smaller sediments but after our tests we found that it had larger sediments.
Discussion and Conclusion
Our results turned out like they did because our curved area was not much different than the straight area that we sampled. Human error should also be accounted for as to why our results came out like they did. One example of this is when we were taking samples from the stream some of the sediment didn’t make it into the bag because when obtaining the samples some of the sediment slipped out from the core before it could have been placed in its proper container. An example of this is when we were running the sediments through the sieves, some of the sediments were lost because it got stuck in the sieves and some went through the filter.
One question that we had was why the straight environment had such a variety of sediment sizes in it. The environment really didn’t fit into any trend that we had in our hypothesis. An explanation that we came up for why this might be is because the straight area that we sampled was coming right off of a curved area therefore larger sediments and smaller sediments were deposited.
We also feel that our results could have benefited if we concentrated our samples in a smaller area. For instance, if we sampled a straight and curved area in the same environment then we could more accurately compare the different sizes of sediments. It would also be easier to find areas that were curved and the water moved more rapidly. For instance the path of the water around a rock could be used as a curved area. The area before or after the rock could be the straight area and then the different size and deposition of sediments could be visualized quite easily.
Additional research that we could have included would be erosion. A test could have been run to determine how the sediment eroding from the stream banks impacted the percentage of that which we found in the water.
September 20-26: First Fifteen Sediment Samples
September 27-3: Lab Packet
October 4-10: Second Set of Sediment Samples*
October 11-17: Second Set..., Water Samples
October 18-24: Second Set..., Lab Analysis of Sediment Samples
October 25-31: Preparation for Presentation/Teaching
November 1- December 10: Work on Final Lab Report
December 11: Final Lab Report Due
1. Sedimentology, Microsoft Encarta 98 Encyclopedia. 1993-1997 Microsoft Corporation. All rights reserved.
2. Lewis, Douglas W., and David McConchie. Analytical Sedimentology. New York: Chapman & Hall, 1994. p. 62
3. Sedimentary Budget Analysis. Mark Mussman, Amanda Rush, Zach Humes, Tim Nance, and Drew Dawson. http://www.muc.miamioh.edu/~spacedog/nsenter.html.
“National Geographic”, volume 191, n 1, January 1997, pg. 2-35
Calculations for Discharge.
1cm3 = 1mL
1mL = .001L
Environment 1 Amount of sediment = 1.47g. x
1000cm3 = 327194.8cm3
x = 480.9g
Environment 2 Amount of sediment = 1.49g. = x
x = 125.8g.
Environment 3 Amount of sediment = 1.51g. = x
x = 176.4g.
480 / 327194.8 *100% = .146%
125.8 / 84449.3 * 100% = .148%
176.4 / 116799 * 100% = .151%
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