Tanyard Creek Virtual Field Trip

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
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.
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.
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
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.
Bibliography
Bryant Watershed Project. (n.d.). Stratigraphy: Rock Layering. Retrieved December 3, 2011, from
watersheds.org: http://www.watersheds.org/earth/layers.htm
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, 1915-1993. Rogers, Arkansas:
RoArk Printing, Inc.
GSA Geologic Time Scale. (n.d.). Retrieved December 2, 2011, from The Geological Society of America:
http://www.geosociety.org/science/timescale/
Invertebrate Fossils. (n.d.). Retrieved December 2, 2011, from Arkansas Geological Survey:
http://www.geology.ar.gov/geology/invert_fossils.htm
Morgan, C. (2011, December 2). Bella Vista Property Owners Association Recreation Manager. (J.
Wedgeworth, Interviewer)
Site A photographs
Site B Photographs
Site C Photographs
Site D Photographs
Site E Photographs