DOC PREVIEW
UT Arlington GEOL 1301 - Geological time
Type Lecture Note
Pages 4

This preview shows page 1 out of 4 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 4 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 4 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

GEOL 1301 Fall 2014 Lecture 10Outline of Last Lecture I. ExamOutline of Current LectureI. Reconstructing geologic history from the stratigraphic record:a. Relative ages What kind of sediments?Have they been tilted?Which layers are oldest, which are youngest? Why are some layers tilted and others aren’t?What does the boundary at top of tilted layers signify? Which layers are oldest, which are youngest? Have the sedimentary layers been tilted? Which layers are oldest? What is the diagonal feature? Is it older or younger than the sediments? 1. Relative Time Reconstructing Geologic History from the Stratigraphic Record You have just articulated the “Principles of Relative Time” • original horizontality• superposition• cross cutting Relationships Example of history of geological events Example of history of geological events What kind of stresses caused the deformation – extension or compression? Example of history of geological events What type of igneous rocks are depicted – intrusive or extrusive? Example of history of geological events What kind of fault is shown – extensional or compressional? Example of history of geological events Relative Geologic Dating 1. Reconstructing Geologic History from the Stratigraphic Record Faunal (fossil) Succession is the last principle of relative time These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.A fossil is any feature in rock made by a once living organism. Both skeletons (right) and tracks (below) are fossils. What is a fossil? Law of Faunal (Fossil) Succession It was discovered around 1810 that fossils changed from one layer to another in a stack of horizontal sedimentary rocks. Moreover, the group of fossils in one set of layers were unique, and different from the fossils in layers either below or above. (right) The Law of Fossil Succession Using the law of superposition, those geologists concluded that one group of fossils had to be older than another group stratigraphically above it. The Law of Fossil Succession This observation led to the “Law of Faunal Succession”: A group of fossils is unique to a particular time period, and that particular fossil group is not found at any other time period. 200 years of observations and radiometric dating have confirmed this “law”. The Law of Fossil Succession The “Law of Faunal Succession” is not based on evolution but the law of superposition. Evolution was described 50 years after “Faunal Succession”. Evolution can explain “faunal Succession” Correlation of sedimentary rocks Correlation is the process of determining whether two rock layers, miles apart, are older,younger or the same age using the law of faunal succession. Since fossils are unique to a particular period of time, layers with the same fossils must be the same age. Correlation of sedimentary rocks Assume the two stratigraphic sections are hundreds of miles apart. Which layers are the same age? Why isn’t layer E and layer A in both sequences? The Principle of Faunal Succession: Fossils as Recorders of Time •Outcrop A •Outcrop B •I •II •II •III •Outcrop A •Outcrop B •I •II •II •III •Outcrop A •Outcrop B •I •II •II •III •Outcrop A •Some of the fossils found in •outcrop A are the same as •fossils found in outcrop B, •some distance away. •Outcrop B•I •II •II •III •Some of the fossils found in •outcrop A are the same as •fossils found in outcrop B, •some distance away. •Outcrop A •Outcrop B •I •II •Layers with the same fossils are the same age. •II •III •Some of the fossils found in •outcrop A are the same as •fossils found in outcrop B, •some distance away. •Outcrop A •Outcrop B •I •II •Layers with the same fossils are the same age. •II •III Correlation of sedimentary rocks Using fossils, rocks in the grand canyon can be correlated with rocks in Zion and Bryce national parks Fossil Succession and Evolution The law of fossil succession (1810) is based on the law of superposition, not evolution, which came 50 years later (1860). Evolution explains why a group of fossils is unique to a particular time period: species become extinct and new ones develop over time. All species living in the distant past disappear going forward in time. The Geologic Relative Time Scale The Geologic time scale consists of time intervals (youngest at the top) that have unique groups of fossils. The oldest intervals (in blue) have few fossils so cannot be divided into relative time periods. The Geologic Relative Time Scale The time intervals are of different lengths: Eons > Eras > Period > Epoch There are 4 Eons: Hadean; Archean; Proterozoic; Phanerozoic Only the Phanerozoic Eon is divided into Eras, Periods and Epochs. Fossils in the older Eons are too scarce to make divisions. The Geologic Relative Time Scale The Geologic Time Scale Each time period has a unique set of fossils. The Geologic Time Scale Unconformities – gaps in the historical record- Disconformity-nogeologicalrecord between parallel sedimentary layers - Nonconformity-nogeologicalrecord between Sedimentary layers and Igneous intrusives - Angularunconformity-nogeological record between sedimentary layers with different tilts Unconformities – gaps in the historical record How can a Disconformity (Sedimentary layers missing in a sequence) be produced by geologic processes? Disconformity Disconformity Disconformity Disconformity Disconformity Summary A nonconformity consists of sediment deposited directly on igneous intrusions or metamorphic rock (light colored rocks in photo). What sequence of geological events could produce that? Nonconformities A nonconformity means that magma was intruded at depth and crystallized. Then overlying rocks were uplifted and eroded exposing the igneous rock at the surface, and then subsidence occurred and sediment was deposited directly on the igneous rock. Angular Unconformities An angular unconformity consists of upper sedimentary layers that are tilted less than the lower ones - i.e. there in an angle between the two groups of layers. Angular Unconformities What sequence of geological events can produce an angular unconformity?. Angular unconformity Angular unconformity Angular unconformity Angular unconformity Angular unconformity The ‘great unconformity’ in the Grand Canyon, Arizona. An angular


View Full Document

UT Arlington GEOL 1301 - Geological time

Type: Lecture Note
Pages: 4
Download Geological time
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Geological time and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Geological time 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?