As caching in New Harmony on one of my trips to hometown in Southern Illinois, I stopped for a cache here and, absolutely, loved this rock... and knew had to make it an Earthcache... I spent much time checking it out, measuring, and walking around & around...
This is One Busy Rock!! There are several very interesting things going on with this rock... the thing that caught my eye first was the tafoni, 2nd. was the splitting, 3rd was the fossils...
So this is going to be a combination EC of those three...
So read the info, check the rock over really good, walk around, do some measurements, read the info...then message me the answers to these questions.. And ENJOY!!
1. Tafoni - a. How many large tafoni holes do you count, the ones you can see through...
b. What colors do you see in the rock?
c. What element is the main cause of tafoni?
2. Splitting - a. How many pieces is the rock in? It still looks like one from a distance, but up close you will be able to make that determination & doing 2b will help you here...
b. What is the circumference of this rock?
c. In addition to tafoni, what other weathering process is causing this rock to split?
3. Fossils - a. Do you see a few or many fossil pieces here?
b. Name the fossil and give me one of the 2 other names it is called...
c. Find & measure one of the largest ones...I see 2 large ones. - (finding answer for 2b should help you here).
Tafoni - may come from Sicilian word “tafoni” for holes, or “tafonare” meaning to perforate...
Tafoni are natural weathering phenomenons, that are pan-to-bowl shaped to small cave-like features found in granular rock such as sandstone, granite, and sandy-limestone… often occurring in groups that riddle a hillside, cliff, or other rocks/ formations…such as this rock…
This weathering is a form of calcium/salt weathering… It occurs when calcium/salt collects on the surface of permeable rocks, usually by ocean waves, mist, or wind. As the saltwater evaporates, it leaves the salt behind. The salt works its way into the rock pores, where it crystallizes and pushes the pores open further, which can become cavities…
With the surface layer of rock being harder than the interior, allows a hardened crust to encompass the softer rock inside, usually a sandstone.. Ran water soaks deep into sandstone mixing with existing calcium/salt… during dry seasons water evaporates from the stone, carrying dissolved calcium/salt to the surface of the stone…as salt is distributed unevenly, there are hard/high and soft /low salt areas… In time when the outer surface areas become cracked and broken, erosion affects the softer areas more quickly…. Wind promotes evaporative salt growth between grains on a stone surface, resulting in the development of small, randomly distributed cavities…Cavity interiors are cooler as are sheltered from the sun…when most air enters a cool cavity, it condenses onto the shadier part of the interior… with differential weathering processes these weather in an upward and backward direction…
These enlarged rock cavities become susceptible to additional weathering including wetting-drying, freezing-thawing cycles, wind corrosion… After a significant amount of time, the weathering becomes noticeable in the form of tafoni.
Splitting - Weathering and erosion in rocks can lead to splitting of the rock..the main weathering process that can lead to this is the freeze and thaw process.. The freeze-thaw cycle is a process of erosion that happens in cold areas where ice forms. A crack in a rock can fill with water which then freezes as the temperature drops. As the ice expands, it pushes the crack apart, making it larger. When the temperature rises again, the ice melts, and the water fills the newer parts of the crack. The water freezes again as the temperature falls, and the expansion of the ice causes further expansion to the crack. This process continues until the rock breaks. (www.ssc.education.ed.ac.uk>BSL Freeze-Thaw Weathering)
Fossils - In this rock you will see pieces of crinoids…. Crinoids are called “sea lilies”, even though are marine animals… When they die, they fall apart and stems or discs is what you will usually see… familiar name is “Indian beads” … I remember collecting many of these growing up in Southern Illinois..
Crinoids first appeared in ancient seas about 300 million years before dinosaurs… they flourished in the Palaeozoic and Mesozoic periods…and some survive today, but in a slightly different appearance…and at over 100 meters deep..
Just another tidbit about Crinoids..they only have 1 hole, meaning that after they eat, they then poop through their mouth…ugh!!
References:
www.nps.gov - tafoni:... urses.lumenlearning.com Weathering and Erosion:... Wiki - tafoni:...
www.3d-fossils.ac.uk.>crinoid:... Illinois State Geological Survey Crinoids;... fossils-facts-and-finds.com - Crinoids, The Down side of the one hole system.