Marcus Geology Field Assignment Part I
- 2. Lake Kaweah is the result of the Terminus dam. It was built in order to form a reservoir from the Kaweah River to draw from for the irrigation of agriculture. The region “was a part of the synclinal basin” during the Paleozoic era (“Geology”). During the Mesozoic and Jurassic periods the geological structure of the area changed greatly ultimately resulting in the Sierra Nevada mountain range from which the Kaweah River flows.
- 3. The cooling of magma forms igneous rocks and as it does so if below ground it crystallizes, if above ground it solidifies. When the process takes place below ground the rocks that form are called intrusive or plutonic. When the process happens above ground the rocks formed are called extrusive or volcanic. Some examples of intrusive igneous rocks are granite, diorite and gabbro. Some examples of extrusive igneous rocks are andesite, obsidian and rhyolite.
- 4. Sample 1- I believe the rock below to be an example of granite, which typically is made of about 25% quartz and 65% feldspar. This particular rock looks to contain a significant amount of dark silicates however this is typical of granite and while it appears this way the dark materials make up generally less than 10% of its composition. Sample 2- The rock above looks to me like Diorite given its darker appearance and lack of quartz crystals as far as I can see. Typical Diorite composition consists of plagioclase feldspar and amphibole with some biotite mixed in. It has a very distinctive contrasting black and white appearance from the feldspar, which is lighter, and the amphibole, which are darker.
- 5. Metamorphic rocks are the result of a metamorphism or change in the chemical structure of the parent rock. Metamorphic rocks are formed when “heat, pressure, and chemically active fluids change” the inherent texture, mineralogy, or chemical composition of a rock (Tarbuck 230). Some examples of metamorphic rocks are slate, marble, quartzite, and mylonite.
- 6. Sample 3- I believe this rock to the right to be quartzite. Pure quartzite is supposed to be white like this rock and its texture is coarse. It is very hard, and shimmers in the light. Quartzite’s parents rock is quartz sandstone and is the result of quartz grains fusing together through “moderate to high-grade metamorphism” (Tarbuck 240). Sample 4- At first I believed this rock at the left to be a sedimentary rock because of the obvious layers. As I researched more I realized that the rock might actually be gneiss, which usually consists of altering dark and light layers. Like this rock gneiss is characteristically coarse and usually occurs with granite as a parent rock, which I also found at the same site.
- 7. Sedimentary Rocks are formed through a long process of weathering, where sediment is carried by water and then settles or is deposited. Over time this forms layers of sediment that compact together to form rocks. “ Diagenesis” is the word used to describe the changes that occur to sediment over time (Tarbuck 201). Some examples of sedimentary rocks include sandstone, breccia, limestone and conglomerate.
- 8. Sample 5- I believe this rock to be arkose because it is a gray/red color and usually occurs in areas where granite is present. It is a detrital sedimentary. It is course and has what appears to be quartz in it. I had the most trouble determining what this rock was because of its small stature.
- 9. “ Geology.” Smithsonian. 2008. http://www.nps.gov/history/history/online_books/smithsonian/terminus-reservoir/sec2.htm . Tarbuck, E. & Lutgens, F. Earth: An Introduction to Physical Geology. 10 th ed. 2011.