Tanyard Creek Virtual Field Trip

Transcription

1 Tanyard Creek Virtual Field Trip NorthWest Arkansas Community College s GEOL 1114 Hybrid Instructor Dr. Wendi J. Williams Student Team Members Cynthia Brantley Cassie Harris Jonathan Mooney David Selby Justin Wedgeworth

2 During the 2011 fall semester, student team members encountered a challenge while trying to complete a field trip at Tanyard Creek Nature Trail in Bella Vista. The class meets each Tuesday at 6 p.m. to accommodate students that work, and by the time we arrived at the site, it was too dark to see within a matter of minutes. The field trip was rescheduled for a different time, but some students had conflicts because of the many other obligations of a community-college student. So our team decided to create a web-based fieldtrip to help students that could not attend the class trip, complete their work. The first stop on the field trip is a bridge that crosses Avalon Branch, a small stream that merges into Tanyard Creek farther along the trail. This river is fed by surface water runoff, springs, and the spillway from Lake Avalon that is located across Arkansas 340 from site A. The Lake was built during the development of Bella Vista by Cooper Communities in the late 1960s for recreation purposes. The lake was built along an existing Avalon Branch river system that now feeds the lake and continues to this location today. (Fite, 1993) The purpose of this site A exercise is to identify components of the topography: channel walls, flood plain, direction and speed of flow, gravel and sand bars learned about in the text as well as concepts introduced in the field such as riffles. Photographs of the area were taken to be included in the Web site that could show students the location of the gravel bar, undercutting of the bank, and give the students an understanding of the processes that take place in the meandering stream. The undercutting occurs near the outside of the stream as the maximum velocity of the stream is shifted to the outside through inertia. As this happens the velocity at the inside of the curve decreases and causes deposition of the gravel bar. (Charles C. Plummer, 2010) The second stop on the field trip lands the student on a gravel bar in front of a limestone bluff. The limestone bluff is exposed and there are limestone gravel that holds many fossils on the gravel.

3 Although in the photographs it is difficult to see under the bluff, there is water underneath that in wetter times, flows into the Avalon Branch. Some of the fossils recovered on the gravel bar are identified as brachiopod and crinoid fossils. The crinoids were a group of marine vertebrates. Most of today s living forms are stemless and live in clear shallow water down to about 200 meters. The source adds that Crinoids are most common in Paleozoic rocks worldwide and in Arkansas are abundant in Late Ordovician and Mississippian age rocks. (Invertebrate Fossils) Brachiopods were soft-bodied marine animals enclosed in a shell, resembling clams. These animals were very abundant during the Paleozoic but gradually gave way to clams. Consequently, brachiopods are common in Paleozoic rocks of Arkansas, whereas clams are far more common in younger rocks. (Invertebrate Fossils) From the discovery of these two fossils, we can estimate the age of the rocks from 460 to 320 million years ago. And we can also see that at that time, our area would have been a marine environment. (GSA Geologic Time Scale) The third location, site C, that we visited on the fieldtrip was the spillway from Lake Windsor that feeds Tanyard Creek. The spillway was constructed in the 1970 s as development of Bella Vista continued. (Morgan, 2011) This was again built to dam an existing stream and the spillway was placed where the water naturally flowed. The purpose of this lake was and continues to be recreation. One of the first things that students notice about the spillway is the deeper channel that leads away from the spillway toward the waterfall. It was there before the dam was built in the 1970s, according to Clem Morgan, Recreation Manager with the Bella Vista Property Owners Association. Morgan lived and played near the creek as a child and remembers that formation.

4 Standing on the dam and looking across the spillway, students can notice rock layers that are exposed. These layers are colored differently. The different beds, and the lines called bedding planes that separate them, record changing conditions while sand and mud were being deposited on the sea floor. By studying this layering, geologists learn volumes about the ancient environments in which the sediments were deposited. (Bryant Watershed Project) A creation of the Windsor Lake Spillway, Tanyard Creek Waterfall, or site D, is one of the more eye-catching portions of the trail. The flowing water creates a path through Boone limestone formations which consist primarily of gray, fine- to coarse-grained fossiliferous limestone mixed with chert. The chert is dark in color in the lower portion of the structure and light in the upper portion. The amount of chert varies noticeably both vertically and horizontally. The Boone limestone consists of oolite near the top of the formation. The Boone formation is well known for dissolutional features, such as sinkholes, caves, and enlarged fissures. Crinoids are the most common fossil found in this limestone formation. The St. Joe limestone formation (formed during the Mississippian period of the Paleozoic era) is a fine-grained, crinoid limestone that may occasionally contain some smoothly bedded chert. The limestone is consistently gray, but may also be red, pink, purple, brown, or amber. The fossils are usually white in contrast to the overall conditions. Thin calcareous shales are found in the limestone structure (top, lower middle, and base). The base of the St. Joe Limestone is generally marked by phosphates, which are usually a greenish shale or conglomerate. These enormous gray boulders (great for forming bluffs) have been around for a long time. Site E brings us to the end of the field trip, where students will notice a strong odor coming from the stream. The odor is caused by a sulfur spring that enters the creek on the right side, if you are looking up stream on the bridge. If you walk over the bridge there is a trail that goes upstream a little

5 way and if you look back you will notice a brown and yellow colored area. This is where the sulfur stream is located. The smell can be caused by the weathering of pyrite or other minerals in the rocks. The smell is similar to rotten eggs and is stronger at times depending on weather conditions. This brings our team to the close of the field trip locations. People can continue along the trail to see more natural beauty from Bella Vista, or head back to the parking lot for home. Either way, this is great place to enjoy nature and learn about the Earth.

6 Bibliography Bryant Watershed Project. (n.d.). Stratigraphy: Rock Layering. Retrieved December 3, 2011, from watersheds.org: Charles C. Plummer, D. H. (2010). Physical Geology: Thirteenth Edition. New York: McGraw-Hill. Fite, G. C. (1993). From Vision to Reality: A History of Bella Vista Village, Rogers, Arkansas: RoArk Printing, Inc. GSA Geologic Time Scale. (n.d.). Retrieved December 2, 2011, from The Geological Society of America: Invertebrate Fossils. (n.d.). Retrieved December 2, 2011, from Arkansas Geological Survey: Morgan, C. (2011, December 2). Bella Vista Property Owners Association Recreation Manager. (J. Wedgeworth, Interviewer)

7 Site A photographs

8 Site B Photographs

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10 Site C Photographs

11 Site D Photographs

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13 Site E Photographs

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