What is Limestone?
Limestone is a sedimentary rock that is found in the state of Tennessee. It contains a large amount of calcium carbonate (in the form of the mineral calcite) and can contain trace amounts of clay, feldspar, iron, and quartz. You can often observe the individual sand grains that make up limestone. Limestone was created by cementation and compaction forces due to sediment deposition via seawater or rivers. The “purest” forms of limestone contain over >98% calcium carbonate and are white in color (i.e., chalk). However, many varieties appear in layers of many colors, ranging from gray to red to yellow, due to the presence of impurities such as iron oxide, organic debris, and sand.
Tennessee Limestone:
Tennessee limestone is a form of sedimentary rock that formed during the formation of Pangaea. Tennessee and other southeastern states were once part of a shallow sea that served as a site for the deposition of sediment. As the African and North American plates converged, the seas dried up, sediment lithified into limestone, and the Appalachian Mountains formed. In eastern Tennessee, the formation of the Appalachian Mountains led to the conversion of sedimentary limestone into metamorphic rock folds (marble) due to immense heat and pressure.
What is grain size?
Grain size refers to the measurement of the length of the diameter of a grain of sediment or a particle embedded in rock (such as limestone). Typically, in Tennessee limestone, sand is the most common particle of sediment found in this type of rock. According to the Udden-Wentworth scale, the grain size of sand is as follows:
- Very fine sand (1/16 – 1/8mm)
- Medium sand (1/4mm – 1/2mm)
- Coarse sand (1/2mm – 1mm)
- Very coarse sand (1 mm – 2mm)
Finding Macroscopic (Visible) Fossils in Limestone:
Tennessee limestone is different from other limestone types as the current-day state's depositional environment only allowed certain areas in the state to contain visible fossils to the naked eye. All limestone types, whether chalk, oolite, or carboniferous rock, contain microscopic fossils. These are usually algae or diatoms that get caught up with sediment fragments and silt that lithify into rock. However, macroscopic fossils are difficult to form, as they depend highly on the sedimentation rate, the depositional environment's temperature, and the amount of pressure. Diagenesis refers to chemical and physical changes due to the transformation of sediment into limestone
Logging Tasks:
- At the GZ, you should notice five limestone boulders. Describe the texture and appearance of the rock.
- Are individual sediment grains visible in the rock? If so, estimate their size according to the Udden-Wentworth scale.
- Some of the boulders are layered. Find a layered limestone specimen and name the rock's different color varieties.
- There are small shell fossils found in some of the limestone boulders. Are more macroscopic fossils found in the unlayered rocks with fewer impurities or the layered specimens with more impurities (more color variation)? Explain why to think this occurs
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://www.britannica.com/science/limestone
https://geokansas.ku.edu/limestone#:~:text=Pure%20limestone%20is%20white%20or,yellow%20to%20gray%20to%20red.
https://www.geologypage.com/2020/08/grain-size-what-is-grain-size-how-is-grain-size-measured.html
https://www.ereferencedesk.com/resources/state-symbols/tennessee/rock.html
Tucker, M. E. (2001). Sedimentary Petrology: An Introduction to the Origin of Sedimentary Rocks (3rd ed.). Wiley-Blackwell.
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