GEOL 1002 Week Two
GEOL 1002 Week Two GEOL 1002-10
Popular in Historical Geology
Popular in Geology
This 2 page Class Notes was uploaded by Gwendolyn Cochran on Thursday January 28, 2016. The Class Notes belongs to GEOL 1002-10 at George Washington University taught by Catherine A. Forster in Spring 2016. Since its upload, it has received 28 views. For similar materials see Historical Geology in Geology at George Washington University.
Reviews for GEOL 1002 Week Two
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 01/28/16
Week Two Sedimentary Rocks: Example: Navajo sandstone (Jurassic) ● nearly pure, rounded quartz sand in enormous desert dune deposits ● note the cross beds Example: Kayenta formations ● siltstone, sandstone, and limestone beds ● ripples at the top indicate running water ● many Jurassic fossils (dinos!!) as well as turtles and frogs The Kayenta formation lies underneath the Navajo sandstone! The kayenta is below, therefore is older. What happened to the environment from Kayenta times to Navajo times? A loss of the water sources! It has gone from a very wet oasis to a dune field. Sedimentary rocks can show us changes in climate over time! Types of sediments 1. Bed Load: heavy material that rolls or jumps along the bottom of a body of water or ground. Think the pebbles that roll on the bottom of a stream 2. Suspended load: sand and rocks suspended in a current; the sand carried in a current about the bottom of the body of water 3. Ripples: avalanches of suspended loads and bed loads that cause cross patterns or ripple patterns over time because of sediments. How to Date Rocks We must know the timing of events, order of events, and rates at which change happened to be able to understand the history of the earth by studying rocks. We can study rocks through these tools: 1. Relative dating a. determines the order b. Using The Law of Superposition the oldests is a the bottom unless it has been disturbed by: i. deformation: folding + titling of tectonic plates ii. igneous intrusions: igneous rock can be injected into already existing rocks through volcanic action 1. dikes cut across (an eruption from below all the layers) 2. sills go with the strata (lava flow across the top of a formation) iii. Faults a complete break of the rock iv. The Law of Cross Cutting Relationships: igneous intrusion or faults are younger than the rock it cuts. Rock has to already be there in order to be cut. 2. Absolute Dating through radiometric dating T = 1/ λ ln[(d/P) + 1] a. This finds the actual numeric age of rocks b. Radioactive decay: different isotopes of different elements decay at different rates: finding the ratio of parent to daughter isotopes and applying the decay constant i. Isotope ii. An isotope can change from unstable to stable; from parent (locked into the crystal structure of the rock) to daughter, through loss of protons or neutron. Over time the ratio of daughter to parent isotope grows. They are both locked into the crystal forever, but decay begins as soon as the crystal is formed c. Radioactive decay happens in a predictable and measurable rate. This is called the decay constant= λ d. All decay is exponential i. Rb^87 Sr^87 the half life is .693 BY ii. Fl^21 Ne^21 the half life is 4.158 seconds iii. K^40 Ar^40 the half life is 1.25 billion years iv. U^235 Pb^207 the half life is 704 million years v. C^14 N^14 the half life is 5730 years (too soon to date rocks) e. You cannot date metamorphic rock this way; and new tech to date precipitated sediment is becoming more widely used; using Uranium. However, this is still generally not used for sedimentary rocks
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'