Park at the western terminus of Rusk St. in the small parking lot. You will note there are no signs here. The parking area is for the Banita Creek Preserve. Walk just past the barrier at the end of Rusk St. and hike North on the trail that begins at the marker with the number "25" on it (the back side of the post has a plaque indicating this is part of the Nacogdoches Ghost Trail). A local Boy Scout group maintains this trail.
Banita Creek has carved some intricate formations into the Weches Formation rocks in the creekbed here. It might help you to complete this cache if you also complete "East Texas Earthcache Series #1: Weches This?" Both of these caches involve the same rock formations in different exposures. In "East Texas Earthcache Series #3: Weches That?" we will examine an exposure of the Weches formation that is very different from that in "East Texas Earthcache Series #1: Weches This?" As you work on this Earthcache, keep in mind the differences in how rocks in the Weches Formation are exposed at the two sites (if you have seen both sites). It is not necessary to do one before the other, but they do complement each other. Since the caches are complementary, much of the background information is the same.
You can find the geologic map covering this area published by the Texas Water Development Board here. The Weches Formation is a member of the Claiborne Group from the Eocene epoch (~45 million years old) in the East Texas Embayment. It is a sedimentary layer with a large amount of variability, but it is composed of glauconitic* muds and greensands, and brown clays and lies between the Queen City and the Sparta Sand Formations. Marine fossils are abundant within this formation. In this portion, the formation is mostly composed of interbedded silts and clays with some fine-grained sands. It ranges in thickness from 110 to 240ft thick, and it is estimated that the sediments formed in seawater of approximately 20°C.
ETE = East Texas Embayment - a historical bay just West of the Mississippi Embayment
illustrated in the above map by the indentation in the coastal plain. A more detailed explanation of the East Texas Embayment is beyond the scope of thie Earthcache, but the details closely parallel those regarding the Mississippi Embayment. Suffice to say that the border of the coastal plain illustrated in the above map illustrates how far inland the coastline actually was prehistorically at various points.
The Weches serves as an impermeable layer between the Sparta and Queen City sands, both of which may contain groundwater usable from wells.
Worth noting, rocks from the Weches Formation weather into alkaline soils of the Trawick and Nacogdoches series. This is unique in the Pineywoods because most soils have an acidic quality to them. The carbonate minerals in the fossils are significant contributors to the alkaline soils. Soils comprised of weathered Weches rocks support a few endemic (occurring nowhere else) plant species.Lesquerella palli (white bladderpod) and Leavenworthia texana (Texas golden glade cress) are two notable endemic plants that can be found in Weches Formation soils. These two species are not currently known on this site, however.
Rocks in the Weches Formation contain high levels of Arsenic (up to 122 mg/kg compared to a global average of 13 mg/kg also here) that can be toxic. Arsenic is common in marine sediments because it substitutes for sulfur in the mineral pyrite. Oxidation of arsenic-bearing pyrite produces acid sulfate conditions, precipitated Fe(OH)3 and oxidized arsenic species. Arsenic adsorbs (sticks) to Fe(OH)3 which is transported to reservoirs by streams and incorporated into the sediment. Be careful not to inhale dust from these rocks or ingest the sediment and wash your hands after handling any. Because arsenic adsorbs so readily to precipitated Fe(OH)3, most of the arsenic is trapped within the sediments at the bottom of reservoirs, which means concentrations in the water rarely exceed the MCL (maximum contaminant level) for arsenic in water.
The Weches also contains averages of about 5ppm of Uranium and about 20ppm of Thorium.
Additional information about local stratigraphy.
*Glauconite is a mineral with a characteristic greenish color in the mica group. It is very friable (crumbly) and has a very low resistance to weathering. It is a characteristic mineral of marine depositional environments.
One feature you may notice in Banita Creek at this site will be small waterfalls.
Waterfalls are formed as a result of water flowing over slowly-eroding resistant bedrock upstream and faster-eroding less resistant bedrock downstream. As the downstream rocks erode away, a shelf of resistant bedrock forms, creating the waterfall. The energy of falling water may develop a plungepool with undercutting, further increasing the height of the waterfall. As undercutting develops, the resistant overhang may slump off. In this manner, a waterfall slowly erodes upstream.
Given the properties of glauconite mentioned above, it is interesting that it is able to form waterfalls. Think about this.
You will also see a number of panholes (or swirlholes) in the rock surface.
Panholes aredepressed, erosional features found on flat or gently sloping rock. Panholes are the result of long-term weathering and are generally seen on bedrock or very large blocks of rock. These shallow solution basins, or closed depressions, tend to form on bare limestone or silicate rock. They are rarely found in granitic rocks. They are generally characterized by flat bottoms and sometimes by overhanging sides.
Swirlholes are holes in rock in a streambed eroded by eddying water, with or without sand or pebbles, typically at the bottom of waterfalls.
Your task is simple. Read about waterfalls and panholes before you head out. Understand what they are and how to identify them.
Once you visit the site of the Earthcache, please do the following tasks, then e-mail the answers to me in a message titled: GC2JRM8: Weches That?
Given that glauconite (and therefore the Weches Formation) is friable and has poor resistance to weathering, how is it that there are waterfalls forming from this particular bedrock?
Visit waypoint Q2. How do these two locations differ in appearance?
Is the stream itself different between the two locations?
Do you think differences in the stream cause the rock to erode the way it has, or do you think differences in the rock have resulted in different erosion patterns?
Why do you think the rock has eroded this way?
Once you determine the answer to these questions, please take your own photos of the waterfalls and panholes at this site as well as at waypoint Q2 and upload them with your log.